On Sun, 04 Mar 2012 22:39:21 -0000, Rod Speed wrote:

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat?

Yeah, its one of those things that seems mad until you realise why its done like that.

It basically reduces the dead zone/hysteresis in the controller.

(It usually just seems to be a resistor
placed near the bi-metallic strip).

Yeah, thats all it is.

All it seems to do for me is make the thermostat very inaccurate.

It actually makes it more accurate, surprisingly enough.

Doesn't seem to work in anyt of the 5 I tried.

Then you have either got it wired up wrong, or arent
actually measuring the hysteresis you are getting with
the heater connected and with it not connected.

There's nothing that can be wired up wrong really. It's only got a neutral, a live, and a switched live. The live and neutral come from the mains, and the switched live goes to an electric fanheater which does not blow at the thermostat.

It's just guessing at the room temperature with that resistor in there.

Nope, because it turns on when the heater isnt on, and only turns
the heater on when the load is turned on, so the load is turned off
earlier than it would otherwise be, reducing the hysteresis.

But the resistor doesn't know how powerful the main heater is, so it could warm the bi-metal strip at at a different rate to the room being warmed up. Now if the resistor was adjustable....

There's quite a bit on it on the net.

If the temperature is only a bit lower outside than inside, the
temperature inside is what I set the stat to. As the temperature
outside drops further, the inside temperature strays further and
further from what I set it to (in the colder direction). This is
presumably because whenever the heating is on, the stat thinks it's
warmer than it really is, because of the internal heater. If I
disconnect this internal heater, the stats functions properly.

Yes, but you will find that the dead zone/hysteresis increases.

I prefer a larger hysteresis

OK, but thats what that part of the design is there for, to reduce that.

Couldn't they have made a better bi-metal strip?

(I'm not that fussy about temperature and wouldn't even notice the house changing temperature by less than about 4C)

Most do notice that much variation.

What on earth do these folk do when they go outside?

than the temperature being just plain wrong.

The temperature isnt just plain wrong. The load is switched on when
the thermostat heater isnt being powered, so the set point isnt affected.

The point at which the the load comes on is fine. But the resistor heats up the bi-metal strip before the load has warmed the room up much, so it's turning it off too soon.

It wouldnt be there at an extra cost if there wasnt a reason for it.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like
this.

Yeah, so did I when I first came across it.

It's more the arcing problem with inductive loads that ****ed me off.

Thats only seen with thermostats that arent meant
to be used with inductive loads are used for those.

Well I've used just about every one I can find and none apart from digital ones work with inductive loads. They all actually state the maximum load with resistive and inductive, so they are designed to work.

--
http://petersparrots.com
http://petersphotos.com

19 Brits have died in the last 3 years believing that christmas decorations were chocolate.

On Sunday, March 4, 2012 9:57:22 PM UTC, Harry Bloomfield wrote:

Wrong! There will always be a natural flow of air because they have
vents top and bottom. The resistor is simply there to reduce
hysteresis.

Why would there be a "natural flow of air" because there are air vents? I know there's ****ing air vents, but the presence of vents does not make the air move. You need an energy input to move air (or anything else). You need a fan or a heat sourcesink that causes convection. Convection currents in the room will not necessarily cause air movement through the thermostat.

Alternative view; the heater in the thermostat WILL generate convection air currents through the thermostat housing. Is this a coincidence? We will never give a stuff.

In article op.wann58raytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 04 Mar 2012 16:38:14 -0000, Graham. wrote:

On Sun, 04 Mar 2012 14:42:26 -0000, "Lieutenant Scott"
wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat? (It usually just seems to be a resistor placed near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate. If the temperature is only a bit lower outside than inside, the temperature inside is what I set the stat to. As the temperature outside drops further, the inside temperature strays further and further from what I set it to (in the colder direction). This is presumably because whenever the heating is on, the stat thinks it's warmer than it really is, because of the internal heater. If I disconnect this internal heater, the stats functions properly.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like this.


It reduces the hysteresis of the system by forcing it to shut off the
heat earlier than it would do naturally.

Hysteresis is a bit like mechanical backlash when a gear chain goes
into reverse.

I know about hysteresis in electronics, but you've lost me with the gears :-)

The contacts need to have an over-centre toggle action for positive
switching, or they would open and close slowly and arc.
The over-centre toggle action requires hysteresis to provide the
two different switching points for opening and closing the contacts.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Sun, 04 Mar 2012 14:42:26 -0000, "Lieutenant Scott"
wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat? (It usually just seems to be a resistor placed near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate. If the temperature is only a bit lower outside than inside, the temperature inside is what I set the stat to. As the temperature outside drops further, the inside temperature strays further and further from what I set it to (in the colder direction). This is presumably because whenever the heating is on, the stat thinks it's warmer than it really is, because of the internal heater. If I disconnect this internal heater, the stats functions properly.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like this.

Your new digital one has very similar functionality in the software.

--

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat?

Yeah, its one of those things that seems mad until you realise why its done like that.

It basically reduces the dead zone/hysteresis in the controller.

(It usually just seems to be a resistor
placed near the bi-metallic strip).

Yeah, thats all it is.

All it seems to do for me is make the thermostat very inaccurate.

It actually makes it more accurate, surprisingly enough.

Doesn't seem to work in anyt of the 5 I tried.

Then you have either got it wired up wrong, or arent
actually measuring the hysteresis you are getting with
the heater connected and with it not connected.

There's nothing that can be wired up wrong really. It's only got a neutral, a live, and a switched live. The live
and neutral come from the mains, and the switched live goes to an electric fanheater which does not blow at the
thermostat.

Turns out you dont care about the hysteresis. The designers do.

It's just guessing at the room temperature with that resistor in there.

Nope, because it turns on when the heater isnt on, and only turns
the heater on when the load is turned on, so the load is turned off
earlier than it would otherwise be, reducing the hysteresis.

But the resistor doesn't know how powerful the main heater is,

It doesnt need to.

so it could warm the bi-metal strip at at a different rate to the room being warmed up. Now if the resistor was
adjustable....

Doesnt need to be.

There's quite a bit on it on the net.

If the temperature is only a bit lower outside than inside, the
temperature inside is what I set the stat to. As the temperature
outside drops further, the inside temperature strays further and
further from what I set it to (in the colder direction). This is
presumably because whenever the heating is on, the stat thinks
it's warmer than it really is, because of the internal heater. If I
disconnect this internal heater, the stats functions properly.

Yes, but you will find that the dead zone/hysteresis increases.

I prefer a larger hysteresis

OK, but thats what that part of the design is there for, to reduce that.

Couldn't they have made a better bi-metal strip?

They did, by including the heater.

(I'm not that fussy about temperature and wouldn't even notice the house changing temperature by less than about 4C)

Most do notice that much variation.

What on earth do these folk do when they go outside?

Thats a different matter to what they prefer when inside.

Yes, I vary what I wear when outside. I prefer not to do that inside.

than the temperature being just plain wrong.

The temperature isnt just plain wrong. The load is switched on when
the thermostat heater isnt being powered, so the set point isnt affected.

The point at which the the load comes on is fine. But the resistor heats up the bi-metal strip before the load has
warmed the room up much, so it's turning it off too soon.

The only effect of that is that it comes on again sooner.

Yes, a proper modern electronic thermostat is better again,
and allows other stuff like time of day and day of week variations
in the set point etc but thats a different matter entirely.

Also true of decent proportional control too.

It wouldnt be there at an extra cost if there wasnt a reason for it.

I've replaced the offending pile of crap with a digital one
anyway, but I wanted to know why they design them like this.

Yeah, so did I when I first came across it.

It's more the arcing problem with inductive loads that ****ed me off.

Thats only seen with thermostats that arent meant
to be used with inductive loads are used for those.

Well I've used just about every one I can find and none apart from digital ones work with inductive loads. They all
actually state the
maximum load with resistive and inductive, so they are designed to work.

You've got a higher inductive load than you think if they wont work with your load.

Yes, you are much better off with a modern digital thermostat.

Thats a separate issue to your original question, why bimetallic thermostats have heaters.

On Sun, 04 Mar 2012 23:29:39 -0000, Andrew Gabriel wrote:

In article op.wann58raytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 04 Mar 2012 16:38:14 -0000, Graham. wrote:

On Sun, 04 Mar 2012 14:42:26 -0000, "Lieutenant Scott"
wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat? (It usually just seems to be a resistor placed near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate. If the temperature is only a bit lower outside than inside, the temperature inside is what I set the stat to. As the temperature outside drops further, the inside temperature strays further and further from what I set it to (in the colder direction). This is presumably because whenever the heating is on, the stat thinks it's warmer than it really is, because of the internal heater. If I disconnect this internal heater, the stats functions properly.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like this.


It reduces the hysteresis of the system by forcing it to shut off the
heat earlier than it would do naturally.

Hysteresis is a bit like mechanical backlash when a gear chain goes
into reverse.

I know about hysteresis in electronics, but you've lost me with the gears :-)

The contacts need to have an over-centre toggle action for positive
switching, or they would open and close slowly and arc.

Maybe that's what mine were all missing (but I did try FIVE different makes and all of them arced).

The over-centre toggle action requires hysteresis to provide the
two different switching points for opening and closing the contacts.

--
http://petersparrots.com
http://petersphotos.com

If you spin oriental folk till they are dizzy, do they become disoriented?

On Sun, 04 Mar 2012 23:37:56 -0000, The Other Mike wrote:

On Sun, 04 Mar 2012 14:42:26 -0000, "Lieutenant Scott"
wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat? (It usually just seems to be a resistor placed near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate. If the temperature is only a bit lower outside than inside, the temperature inside is what I set the stat to. As the temperature outside drops further, the inside temperature strays further and further from what I set it to (in the colder direction). This is presumably because whenever the heating is on, the stat thinks it's warmer than it really is, because of the internal heater. If I disconnect this internal heater, the stats functions properly.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like this.

Your new digital one has very similar functionality in the software.

No, all it does is switch the load on at 0.5C below what I set it to, and switch it off at 0.5C above what I set it to.

--
http://petersparrots.com
http://petersphotos.com

Are you into casual sex, or should I dress up?

Onetap wrote
Harry Bloomfield wrote

Wrong! There will always be a natural flow of air because they have
vents top and bottom. The resistor is simply there to reduce hysteresis.

Why would there be a "natural flow of air" because there are air
vents? I know there's ****ing air vents, but the presence of vents
does not make the air move. You need an energy input to move air (or
anything else). You need a fan or a heat sourcesink that causes
convection. Convection currents in the room will not necessarily
cause air movement through the thermostat.

Alternative view; the heater in the thermostat WILL generate convection
air currents through the thermostat housing. Is this a coincidence?

If it was JUST there to move the air, you'd have it at the top,
and where it doesnt radiate to the bi metallic strip. AND
you'd have it on all the time, not just when the load is on.

We will never give a stuff.

On Sun, 04 Mar 2012 23:39:40 -0000, Rod Speed wrote:

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote



Yeah, its one of those things that seems mad until you realise why its done like that.

It basically reduces the dead zone/hysteresis in the controller.



Yeah, thats all it is.



It actually makes it more accurate, surprisingly enough.

Doesn't seem to work in anyt of the 5 I tried.

Then you have either got it wired up wrong, or arent
actually measuring the hysteresis you are getting with
the heater connected and with it not connected.

There's nothing that can be wired up wrong really. It's only got a neutral, a live, and a switched live. The live
and neutral come from the mains, and the switched live goes to an electric fanheater which does not blow at the
thermostat.

Turns out you dont care about the hysteresis. The designers do.

It's just guessing at the room temperature with that resistor in there.

Nope, because it turns on when the heater isnt on, and only turns
the heater on when the load is turned on, so the load is turned off
earlier than it would otherwise be, reducing the hysteresis.

But the resistor doesn't know how powerful the main heater is,

It doesnt need to.

so it could warm the bi-metal strip at at a different rate to the room being warmed up. Now if the resistor was
adjustable....

Doesnt need to be.

So explain why mine is rubbish?

Yes, but you will find that the dead zone/hysteresis increases.

I prefer a larger hysteresis

OK, but thats what that part of the design is there for, to reduce that.

Couldn't they have made a better bi-metal strip?

They did, by including the heater.

I meant the actual strip. Thus negating the need for a workaround.

(I'm not that fussy about temperature and wouldn't even notice the house changing temperature by less than about 4C)

Most do notice that much variation.

What on earth do these folk do when they go outside?

Thats a different matter to what they prefer when inside.

Yes, I vary what I wear when outside. I prefer not to do that inside.

Are you cold blooded like a lizard?

than the temperature being just plain wrong.

The temperature isnt just plain wrong. The load is switched on when
the thermostat heater isnt being powered, so the set point isnt affected.

The point at which the the load comes on is fine. But the resistor heats up the bi-metal strip before the load has
warmed the room up much, so it's turning it off too soon.

The only effect of that is that it comes on again sooner.

But if the heating is required to be on an 90% duty cycle to keep the room at the requested temperature, the thermostat never achieves this. The insided of the thermostat are getting quite warm due to the resistor, but the room isn't.

Yes, a proper modern electronic thermostat is better again,
and allows other stuff like time of day and day of week variations
in the set point etc but thats a different matter entirely.

They still seem to be selling these bi-metal things, even though an electronic one doesn't cost much more now.

Also true of decent proportional control too.

What is one of those?

Yeah, so did I when I first came across it.

It's more the arcing problem with inductive loads that ****ed me off.

Thats only seen with thermostats that arent meant
to be used with inductive loads are used for those.

Well I've used just about every one I can find and none apart from digital ones work with inductive loads. They all
actually state the
maximum load with resistive and inductive, so they are designed to work.

You've got a higher inductive load than you think if they wont work with your load.

It's only a motorized valve. The pump and boiler are switched by the contacts in the motorized valve, that current doesn't go through the thermostat contacts.

--
http://petersparrots.com
http://petersphotos.com

Why do they rate a movie "R" for "adult language?"
The only people I hear using that language are teenagers.

On Sunday, March 4, 2012 11:42:35 PM UTC, Rod Speed wrote:

If it was JUST there to move the air, you'd have it at the top,
and where it doesnt radiate to the bi metallic strip. AND
you'd have it on all the time, not just when the load is on.

Who said it was JUST there to move the air?
It does move the air though.

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote

Yeah, its one of those things that seems mad until you realise why its done like that.

It basically reduces the dead zone/hysteresis in the controller.

Yeah, thats all it is.

It actually makes it more accurate, surprisingly enough.

Doesn't seem to work in anyt of the 5 I tried.

Then you have either got it wired up wrong, or arent
actually measuring the hysteresis you are getting with
the heater connected and with it not connected.

There's nothing that can be wired up wrong really. It's only got a neutral, a live, and a switched live. The live
and neutral come from the mains, and the switched live goes to an electric fanheater which does not blow at the
thermostat.

Turns out you dont care about the hysteresis. The designers do.

It's just guessing at the room temperature with that resistor in there.

Nope, because it turns on when the heater isnt on, and only turns
the heater on when the load is turned on, so the load is turned off
earlier than it would otherwise be, reducing the hysteresis.

But the resistor doesn't know how powerful the main heater is,

It doesnt need to.

so it could warm the bi-metal strip at at a different rate to the
room being warmed up. Now if the resistor was adjustable....

Doesnt need to be.

So explain why mine is rubbish?

Maybe its just a lousy design.

Yes, but you will find that the dead zone/hysteresis increases.

I prefer a larger hysteresis

OK, but thats what that part of the design is there for, to reduce that.

Couldn't they have made a better bi-metal strip?

They did, by including the heater.

I meant the actual strip. Thus negating the need for a workaround.

It isnt even possible and the heater isnt a workaround, its a significant
design feature which does what its designed to do, reduce the hysteresis.

If you dont like how it performs, it makes more sense to go digital and
get all sorts of other advantages like time of day and day of week stuff
too and automatic proportional mode with loads that can do that.

(I'm not that fussy about temperature and wouldn't even notice
the house changing temperature by less than about 4C)

Most do notice that much variation.

What on earth do these folk do when they go outside?

Thats a different matter to what they prefer when inside.

Yes, I vary what I wear when outside. I prefer not to do that inside.

Are you cold blooded like a lizard?

Yeah, I am. I have always preferred rooms warmer than anyone else, and
dont mind hot weather when everyone else is bitching about how hot it is.

I have to remember to turn the cooler on when visitors show
up, I dont even think about turning it on till it gets over 31C

And have a top on over the T shirt before anyone else does when out too.

than the temperature being just plain wrong.

The temperature isnt just plain wrong. The load is switched on when
the thermostat heater isnt being powered, so the set point isnt affected.

The point at which the the load comes on is fine. But the resistor heats up the bi-metal strip before the load has
warmed the room up much, so it's turning it off too soon.

The only effect of that is that it comes on again sooner.

But if the heating is required to be on an 90% duty cycle to keep the
room at the requested temperature, the thermostat never achieves this.

Sure, but most do size the heater properly and prefer the lower hysteresis.

Obviously a decent modern digital thermostat handles that much better.

The insided of the thermostat are getting quite warm due to the resistor, but the room isn't.

Yes, a proper modern electronic thermostat is better again,
and allows other stuff like time of day and day of week variations
in the set point etc but thats a different matter entirely.

They still seem to be selling these bi-metal things, even though an electronic one doesn't cost much more now.

Yeah, you can get some bizarre stuff like that.

The best digital thermostats do cost quite a bit more than
the cheapest bi metallic thermostats from china tho.

Also true of decent proportional control too.

What is one of those?

Proportinal control adjusts the power output of the load rather than
just turning it off or on. So you can have 61%, 62% etc etc etc.

Corse not all loads can do that.

Yeah, so did I when I first came across it.

It's more the arcing problem with inductive loads that ****ed me off.

Thats only seen with thermostats that arent meant
to be used with inductive loads are used for those.

Well I've used just about every one I can find and none apart from
digital ones work with inductive loads. They all actually state the
maximum load with resistive and inductive, so they are designed to work.

You've got a higher inductive load than you think if they wont work with your load.

It's only a motorized valve. The pump and boiler are switched by the contacts in the motorized valve, that current
doesn't go through the thermostat contacts.

That though depends on the site of the stat, and how well designed the
placement of the radiators were in the first place.
Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"A.Lee" wrote in message
.. .
DerekG wrote:

It's a bit like trying to throw a Yo-Yo away whilst still holding onto
the string. And yes it's a crap plumbers idea.


It isnt. I've been on a training course that shows the graphs of heat
and gas used. The heated stats use less gas, and keep the room at a
steadier temperature than the standard on/off stats.

Alan.

--
To reply by e-mail, change the ' + ' to 'plus'.

In article op.wan2p2cbytk5n5@i7-940, Lieutenant Scott wrote:


[Snip]

And just how would I change the installation? There is no adjustment to
make!

3 wires - 3 teminals - that's 6 wiring combinations.

--
From KT24

Using a RISC OS computer running v5.18

Onetap explained :
On Sunday, March 4, 2012 9:57:22 PM UTC, Harry Bloomfield wrote:

Wrong! There will always be a natural flow of air because they have
vents top and bottom. The resistor is simply there to reduce
hysteresis.

Why would there be a "natural flow of air" because there are air vents? I
know there's ****ing air vents, but the presence of vents does not make the
air move. You need an energy input to move air (or anything else). You need
a fan or a heat sourcesink that causes convection. Convection currents in the
room will not necessarily cause air movement through the thermostat.

Alternative view; the heater in the thermostat WILL generate convection
air currents through the thermostat housing. Is this a coincidence? We will
never give a stuff.

If there were no natural air flow, without the heater resistor to
encourage it, then the thing would take forever to sense the falling
temperature when the stat opens. The fact is that it doesn't, because
there is air flow through the stat, irrespective of whether the
resistor is energised or not.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

on 04/03/2012, Rod Speed supposed :
You should see the biggest difference with the lowest outside temps.

Having just checked - there was no noticeable difference, once a
settled temperature was achieved. There were much bigger temperature
swings when a door was opened in cold conditions, but once back to a
settled condition no obvious difference other than the more rapid
firing of the heating.


And you dont have the figures for a bi metallic thermostat with no heater.

If you did, it would have a higher range again.

Agreed! I would expect temperature swings of at a guess 5 deg C, with
no resistor in place.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Mon, 05 Mar 2012 03:20:14 -0000, Rod Speed wrote:

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Nope, because it turns on when the heater isnt on, and only turns
the heater on when the load is turned on, so the load is turned off
earlier than it would otherwise be, reducing the hysteresis.

But the resistor doesn't know how powerful the main heater is,

It doesnt need to.

so it could warm the bi-metal strip at at a different rate to the
room being warmed up. Now if the resistor was adjustable....

Doesnt need to be.

So explain why mine is rubbish?

Maybe its just a lousy design.

All five of them? Different makes?

OK, but thats what that part of the design is there for, to reduce that.

Couldn't they have made a better bi-metal strip?

They did, by including the heater.

I meant the actual strip. Thus negating the need for a workaround.

It isnt even possible and the heater isnt a workaround, its a significant
design feature which does what its designed to do, reduce the hysteresis.

It means the thermostat is guessing at the temperature, as the actual sensor is picking up artificial heat from the resistor. I would not call that a good design. It may well have been the best the technology could come up with before digital ones, but it's still rubbish, and from my experience of five of them, they make things worse.

If you dont like how it performs, it makes more sense to go digital and
get all sorts of other advantages like time of day and day of week stuff
too and automatic proportional mode with loads that can do that.

Yes I now have done.

Most do notice that much variation.

What on earth do these folk do when they go outside?

Thats a different matter to what they prefer when inside.

Yes, I vary what I wear when outside. I prefer not to do that inside.

Are you cold blooded like a lizard?

Yeah, I am. I have always preferred rooms warmer than anyone else, and
dont mind hot weather when everyone else is bitching about how hot it is.

I have to remember to turn the cooler on when visitors show
up, I dont even think about turning it on till it gets over 31C

And have a top on over the T shirt before anyone else does when out too.

I do not wear two layers at any time of year. I know someone else who feels the cold and not the heat like you - they said they have a vitamin D deficiency and anaemia.

The temperature isnt just plain wrong. The load is switched on when
the thermostat heater isnt being powered, so the set point isnt affected.

The point at which the the load comes on is fine. But the resistor heats up the bi-metal strip before the load has
warmed the room up much, so it's turning it off too soon.

The only effect of that is that it comes on again sooner.

But if the heating is required to be on an 90% duty cycle to keep the
room at the requested temperature, the thermostat never achieves this.

Sure, but most do size the heater properly and prefer the lower hysteresis.

So for the sake of a crap thermostat, the answer is to have a heater capable of heating the room with a 50% duty cycle? Oh dear.

Obviously a decent modern digital thermostat handles that much better.

The insided of the thermostat are getting quite warm due to the resistor, but the room isn't.

Yes, a proper modern electronic thermostat is better again,
and allows other stuff like time of day and day of week variations
in the set point etc but thats a different matter entirely.

They still seem to be selling these bi-metal things, even though an electronic one doesn't cost much more now.

Yeah, you can get some bizarre stuff like that.

The best digital thermostats do cost quite a bit more than
the cheapest bi metallic thermostats from china tho.

The cheapest digital thermostat works perfectly.

Also true of decent proportional control too.

What is one of those?

Proportinal control adjusts the power output of the load rather than
just turning it off or on. So you can have 61%, 62% etc etc etc.

Corse not all loads can do that.

I suppose theoretically a central heating boiler could do this if you could interface the room stat with the water temp stat.

--
http://petersparrots.com
http://petersphotos.com

An expert is someone who takes a subject you understand and makes it sound confusing.

On Mon, 05 Mar 2012 08:24:06 -0000, charles wrote:

In article op.wan2p2cbytk5n5@i7-940, Lieutenant Scott wrote:


[Snip]

And just how would I change the installation? There is no adjustment to
make!

3 wires - 3 teminals - that's 6 wiring combinations.

I have a degree in Digital Microelectronics, I'm not likely to get mixed up with three wires :-)

--
http://petersparrots.com
http://petersphotos.com

You wag your tail like your mother, you repugnant, hairball engorging, cat buggering, pseudo-human android spawn of a foul-smelling telephone solicitor!

On Mon, 05 Mar 2012 11:17:31 -0000, "Lieutenant Scott"
wrote:

On Mon, 05 Mar 2012 08:24:06 -0000, charles wrote:

In article op.wan2p2cbytk5n5@i7-940, Lieutenant Scott wrote:


[Snip]

And just how would I change the installation? There is no adjustment to
make!

3 wires - 3 teminals - that's 6 wiring combinations.

I have a degree in Digital Microelectronics, I'm not likely to get mixed up with three wires :-)

Does the heater resistor connect to data, clock or ground?

--
Graham.
%Profound_observation%

On Mon, 05 Mar 2012 12:12:59 -0000, Graham. wrote:

On Mon, 05 Mar 2012 11:17:31 -0000, "Lieutenant Scott"
wrote:

On Mon, 05 Mar 2012 08:24:06 -0000, charles wrote:

In article op.wan2p2cbytk5n5@i7-940, Lieutenant Scott wrote:


[Snip]

And just how would I change the installation? There is no adjustment to
make!

3 wires - 3 teminals - that's 6 wiring combinations.

I have a degree in Digital Microelectronics, I'm not likely to get mixed up with three wires :-)

Does the heater resistor connect to data, clock or ground?

I suppose you'd call it data, as it's wired to the output which is switched on by the stat.

--
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You can't polish a turd, but it's funny as **** watching someone try.

On Mar 5, 12:19*pm, "Lieutenant Scott" wrote:
I suppose you'd call it data, as it's wired to the output which is switched on by the stat.

For the resistor to work it must have a neutral.

On Mon, 05 Mar 2012 13:34:54 -0000, js.b1 wrote:

On Mar 5, 12:19 pm, "Lieutenant Scott" wrote:
I suppose you'd call it data, as it's wired to the output which is switched on by the stat.

For the resistor to work it must have a neutral.

GND (neutral) was assumed. I was answering where you connected the other end.

--
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By far the best engine in the world is the "Fanny":
It pulls anything, starts with one finger, self lubricates, takes any sized piston,
then every 4 weeks it does it's own oil change. It's just a pity that the management
system is so ****ing temperamental!

On Mon, 05 Mar 2012 09:36:16 GMT, Harry Bloomfield
wrote:

Onetap explained :
On Sunday, March 4, 2012 9:57:22 PM UTC, Harry Bloomfield wrote:

Wrong! There will always be a natural flow of air because they have
vents top and bottom. The resistor is simply there to reduce
hysteresis.

Why would there be a "natural flow of air" because there are air vents? I
know there's ****ing air vents, but the presence of vents does not make the
air move. You need an energy input to move air (or anything else). You need
a fan or a heat sourcesink that causes convection. Convection currents in the
room will not necessarily cause air movement through the thermostat.

Alternative view; the heater in the thermostat WILL generate convection
air currents through the thermostat housing. Is this a coincidence? We will
never give a stuff.

If there were no natural air flow, without the heater resistor to
encourage it, then the thing would take forever to sense the falling
temperature when the stat opens. The fact is that it doesn't, because
there is air flow through the stat, irrespective of whether the
resistor is energised or not.

The other thing Onetap might consider is that the resistor body is
physically in contact with strip (at least it is on this old Satchwell
I have on the desk), so the design was to heat the strip by conduction
primarily.

The other thing worth mentioning is that the contacts are magnetised
to give the thermistat a snap action to prevent arcing and RFI

--
Graham.
%Profound_observation%

Oops, sent to early
The other thing worth mentioning is that the contacts are magnetised
to give the thermistat a snap action to prevent arcing and RFI
and this is what contributes most of all to the hysteresis IMHO

--
Graham.
%Profound_observation%

On Mon, 05 Mar 2012 13:55:41 -0000, "Lieutenant Scott"
wrote:

On Mon, 05 Mar 2012 13:34:54 -0000, js.b1 wrote:

On Mar 5, 12:19 pm, "Lieutenant Scott" wrote:
I suppose you'd call it data, as it's wired to the output which is switched on by the stat.

For the resistor to work it must have a neutral.

GND (neutral) was assumed. I was answering where you connected the other end.

OK confession time.
For a long time I had the neutral terminal of my room stat connected
to the CPC because there was no neutral. The CU didn't contain an RCD
at the time

--
Graham.
%Profound_observation%

On Sun, 4 Mar 2012 23:29:39 +0000 (UTC),
(Andrew Gabriel) wrote:

In article op.wann58raytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 04 Mar 2012 16:38:14 -0000, Graham. wrote:

On Sun, 04 Mar 2012 14:42:26 -0000, "Lieutenant Scott"
wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat? (It usually just seems to be a resistor placed near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate. If the temperature is only a bit lower outside than inside, the temperature inside is what I set the stat to. As the temperature outside drops further, the inside temperature strays further and further from what I set it to (in the colder direction). This is presumably because whenever the heating is on, the stat thinks it's warmer than it really is, because of the internal heater. If I disconnect this internal heater, the stats functions properly.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like this.


It reduces the hysteresis of the system by forcing it to shut off the
heat earlier than it would do naturally.

Hysteresis is a bit like mechanical backlash when a gear chain goes
into reverse.

I know about hysteresis in electronics, but you've lost me with the gears :-)

The contacts need to have an over-centre toggle action for positive
switching, or they would open and close slowly and arc.
The over-centre toggle action requires hysteresis to provide the
two different switching points for opening and closing the contacts.

Often by incorporating a magnet in the contact arrangement.

--
Graham.
%Profound_observation%

On Mon, 05 Mar 2012 15:21:09 -0000, Graham. wrote:

On Mon, 05 Mar 2012 13:55:41 -0000, "Lieutenant Scott"
wrote:

On Mon, 05 Mar 2012 13:34:54 -0000, js.b1 wrote:

On Mar 5, 12:19 pm, "Lieutenant Scott" wrote:
I suppose you'd call it data, as it's wired to the output which is switched on by the stat.

For the resistor to work it must have a neutral.

GND (neutral) was assumed. I was answering where you connected the other end.

OK confession time.
For a long time I had the neutral terminal of my room stat connected
to the CPC because there was no neutral. The CU didn't contain an RCD
at the time

They're the same thing anyway :-)

I do the same for convenience. I have no RCD and never will. Horrid things.

--
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Whatever hits the fan will not be evenly distributed.

On Mon, 05 Mar 2012 15:24:34 -0000, Graham. wrote:

On Sun, 4 Mar 2012 23:29:39 +0000 (UTC),
(Andrew Gabriel) wrote:

In article op.wann58raytk5n5@i7-940,
"Lieutenant Scott" writes:
On Sun, 04 Mar 2012 16:38:14 -0000, Graham. wrote:

On Sun, 04 Mar 2012 14:42:26 -0000, "Lieutenant Scott"
wrote:

Can someone explain the use of a heater INSIDE a mechanical (bimetal strip) room thermostat? (It usually just seems to be a resistor placed near the bi-metallic strip).

All it seems to do for me is make the thermostat very inaccurate. If the temperature is only a bit lower outside than inside, the temperature inside is what I set the stat to. As the temperature outside drops further, the inside temperature strays further and further from what I set it to (in the colder direction). This is presumably because whenever the heating is on, the stat thinks it's warmer than it really is, because of the internal heater. If I disconnect this internal heater, the stats functions properly.

I've replaced the offending pile of crap with a digital one anyway, but I wanted to know why they design them like this.


It reduces the hysteresis of the system by forcing it to shut off the
heat earlier than it would do naturally.

Hysteresis is a bit like mechanical backlash when a gear chain goes
into reverse.

I know about hysteresis in electronics, but you've lost me with the gears :-)

The contacts need to have an over-centre toggle action for positive
switching, or they would open and close slowly and arc.
The over-centre toggle action requires hysteresis to provide the
two different switching points for opening and closing the contacts.

Often by incorporating a magnet in the contact arrangement.

Maybe mine don't have magnets, hence the arcing.

--
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http://petersphotos.com

Sex drive: a physical craving that begins in adolescence and ends at marriage.

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Nope, because it turns on when the heater isnt on, and only turns
the heater on when the load is turned on, so the load is turned
off earlier than it would otherwise be, reducing the hysteresis.

But the resistor doesn't know how powerful the main heater is,

It doesnt need to.

so it could warm the bi-metal strip at at a different rate to the
room being warmed up. Now if the resistor was adjustable....

Doesnt need to be.

So explain why mine is rubbish?

Maybe its just a lousy design.

All five of them? Different makes?

I meant what you are controlling with them. I just dont believe
that everyone has the same problem you have finding a bi
metallic strip thermostat that will actually switch the load you
are switching and they all ove to use digital thermostats instead.

OK, but thats what that part of the design is there for, to
reduce that.

Couldn't they have made a better bi-metal strip?

They did, by including the heater.

I meant the actual strip. Thus negating the need for a workaround.

It isnt even possible and the heater isnt a workaround, its a significant design feature which does what its designed
to do, reduce the hysteresis.

It means the thermostat is guessing at the temperature,

No it does not. When used properly, the heater is ONLY on when
the load is on and so there is no guessing what so ever involved.

The ONLY thing the heater does is cause the thermostat to turn
OFF earlier than it would otherwise do without a heater and even
that isnt a guess, its a deliberate choice by the designer to do that.

as the actual sensor is picking up artificial heat from the resistor.

Not when its turning on with the heater turned off it isnt.

I would not call that a good design.

It is anyway, because the heater reduces the inevitable
hysteresis that you get with a bimetallic strip thermostat.

It may well have been the best the technology could come up with before digital ones,

It obviously was. You wont be able to find a better design
improvement with bi metallic thermostats than that.

but it's still rubbish, and from my experience of five of them, they make things worse.

Only in the sense that they switch more often than without the heater.

There is no other way to reduce the hysteresis.

You dont care about hysteresis ? You're always welcome to disconnect the heater.

If you dont like how it performs, it makes more sense to go digital
and get all sorts of other advantages like time of day and day of week stuff too and automatic proportional mode with
loads that can do that.

Yes I now have done.

Most do notice that much variation.

What on earth do these folk do when they go outside?

Thats a different matter to what they prefer when inside.

Yes, I vary what I wear when outside. I prefer not to do that inside.

Are you cold blooded like a lizard?

Yeah, I am. I have always preferred rooms warmer than anyone else, and dont mind hot weather when everyone else is
bitching about how hot it is.

I have to remember to turn the cooler on when visitors show
up, I dont even think about turning it on till it gets over 31C

And have a top on over the T shirt before anyone else does when out too.

I do not wear two layers at any time of year.

Then you are very unusual indeed. Even more unusual than me.

I know someone else who feels the cold and not the heat like you - they said they have a vitamin D deficiency and
anaemia.

Interesting you should say that. A mate of mine who is rather
younger than me has just discovered that he has a vitamin D
deficiency when he got a blood test for something else entirely.
Unfortunately I get the form for my annual blood test at the GP
consultation the year before I actually get the test, so the GP
has the results of the test when I show up for the annual consult
so I couldnt get a vitamin D test included in my blood test. I will
do so next time, because he is outside quite a bit and he shouldnt
have a vitamin D deficiency in theory.

But he is the main one who complains about how warm it is when he
shows up here and I dont have the cooler on in the warm weather. So
thats a problem with the theory that its a vitamin D deficiency in my case.

And I have always been like that temperature wise even as a kid.

The temperature isnt just plain wrong. The load is switched on when the thermostat heater isnt being powered, so
the set point isnt affected.

The point at which the the load comes on is fine. But the
resistor heats up the bi-metal strip before the load has warmed the room up much, so it's turning it off too
soon.

The only effect of that is that it comes on again sooner.

But if the heating is required to be on an 90% duty cycle to keep the room at the requested temperature, the
thermostat never achieves this.

Sure, but most do size the heater properly and prefer the lower hysteresis.

So for the sake of a crap thermostat, the answer is to have a heater capable of heating the room with a 50% duty
cycle?

Nope, most care more about hysteresis than they do about
the frequency of switching, so a heater is included with the
better bi metallic thermostats. Some of them allow you to
not connect the heater if you dont want it.

And it isnt just room heater thermostats either, they are seen with cars etc too.

Oh dear.

Obviously a decent modern digital thermostat handles that much better.

The insided of the thermostat are getting quite warm due to the
resistor, but the room isn't.

Yes, a proper modern electronic thermostat is better again,
and allows other stuff like time of day and day of week variations
in the set point etc but thats a different matter entirely.

They still seem to be selling these bi-metal things, even though an electronic one doesn't cost much more now.

Yeah, you can get some bizarre stuff like that.

The best digital thermostats do cost quite a bit more than
the cheapest bi metallic thermostats from china tho.

The cheapest digital thermostat works perfectly.

Sure, but the cheapest bi metallic strip thermostat is cheaper
again, particularly when its what was there all along and you are
considering replacing it with a proper modern digital thermostat.

And if you care about the cost, you should really be using
a decent modern digital thermostat that includes day and
week time bands too, because that will very quickly pay
for itself in reduced heating costs if you arent prepared to
keep manually fiddling with the thermostat every day etc.

Also true of decent proportional control too.

What is one of those?

Proportinal control adjusts the power output of the load rather than
just turning it off or on. So you can have 61%, 62% etc etc etc.

Corse not all loads can do that.

I suppose theoretically a central heating boiler could do this if you could interface the room stat with the water
temp stat.

And that isnt the only way to do that either.

Corse there isnt any point in your case because you dont care about hysteresis.

Most do tho.

On Mar 5, 3:21*pm, Graham. wrote:
OK confession time.
For a long time I had the neutral terminal of my room stat connected
to the CPC because there was no neutral. The CU didn't contain an RCD
at the time

SI 2002 #2665, ESQCR.
"A consumer shall not combine the neutral and protective functions in
a single conductor in his consumer's installation."

Reason being whilst the earth tests as dead, when you disconnect the
CU earth then every single (electrically) earthed object in the house
including gas & water pipes re MEB is now a floating live whose
ability to shock is only limited by the resistor (in this case).

So the next time John Prescott comes around... :-)

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Doesnt need to be.

So explain why mine is rubbish?

Maybe its just a lousy design.

All five of them? Different makes?

I meant what you are controlling with them. I just dont believe
that everyone has the same problem you have finding a bi
metallic strip thermostat that will actually switch the load you
are switching and they all ove to use digital thermostats instead.

Must be the motorized valve is sticking and presenting a very big starting load?

Its gotta be something like that that sees 5 different bi metallic thermostats
arcing instead of switching cleanly.

Unless you somehow managed to end up with 5 completely different ones
with no magnetic contacts that stop arcing which sounds very unlikely indeed.

It's never had a problem opening.

Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

Where did you get its inductive load figure from ?

They did, by including the heater.

I meant the actual strip. Thus negating the need for a workaround.

It isnt even possible and the heater isnt a workaround, its a significant design feature which does what its
designed to do, reduce the hysteresis.

It means the thermostat is guessing at the temperature,

No it does not. When used properly, the heater is ONLY on when
the load is on and so there is no guessing what so ever involved.

The ONLY thing the heater does is cause the thermostat to turn
OFF earlier than it would otherwise do without a heater and even
that isnt a guess, its a deliberate choice by the designer to do that.

If it was accurate enough so that the resistor increased the temperature inside the stat by exactly 2 degrees,

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

then it would reduce the hysteresis from 3C to 1C, but I doubt a resistor placed close to a bi-metallic strip is that
accurate. It depends on air movement in the room for a start.

And the room temp too.

And the hysteresis with a bi metallic strip thermostat is essentially
determined by the magnetic contacts that are there to stop arcing,
and those dont have a rigidly specified temperature hysteresis anyway.

That isnt even possible either.

I would not call that a good design.

It is anyway, because the heater reduces the inevitable
hysteresis that you get with a bimetallic strip thermostat.

Why on earth do people feel the need to have such a precise control of temperature anyway?

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

Most people have more than a 1 degree comfort range.

And you dont get that with a bi metallic strip thermostat with no heater.

Thats a different matter to what they prefer when inside.

Yes, I vary what I wear when outside. I prefer not to do that inside.

Are you cold blooded like a lizard?

Yeah, I am. I have always preferred rooms warmer than anyone else, and dont mind hot weather when everyone else is
bitching about how hot it is.

I have to remember to turn the cooler on when visitors show
up, I dont even think about turning it on till it gets over 31C

And have a top on over the T shirt before anyone else does when out too.

I do not wear two layers at any time of year.

Then you are very unusual indeed. Even more unusual than me.

I prefer superior.

I know someone else who feels the cold and not the heat like you - they said they have a vitamin D deficiency and
anaemia.

Interesting you should say that. A mate of mine who is rather
younger than me has just discovered that he has a vitamin D
deficiency when he got a blood test for something else entirely.
Unfortunately I get the form for my annual blood test at the GP
consultation the year before I actually get the test, so the GP
has the results of the test when I show up for the annual consult
so I couldnt get a vitamin D test included in my blood test. I will
do so next time, because he is outside quite a bit and he shouldnt
have a vitamin D deficiency in theory.

But I definitely an not anaemic.

The person I'm thinking of doesn't expose much skin to sunlight.

Yeah, I realise thats why most end up with a Vitamin D deficiency.

Thats why I mentioned that he doesnt have that problem.

Neither do I.

Do sunlamps work?

Dunno, he's taking pills, but hasnt had a second test to see if they are working for him.

But he is the main one who complains about how warm it is when he
shows up here and I dont have the cooler on in the warm weather. So
thats a problem with the theory that its a vitamin D deficiency in my case.

I know nothing about the illnesses, so maybe the anaemia?

Nope, I know I dont have that.

And I have always been like that temperature wise even as a kid.

I'm sure you could train yourself to become accustomed to it.

Sure, but there isnt any point in doing that, I prefer to be comfortable instead.

And its no big deal to put a top on over the T shirt before anyone else does.

And I save power in summer when I put the cooler on well after everyone else does.

The house was designed passive solar so I bask in the sun on sunny
days in winter and everyone who visits comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

The only effect of that is that it comes on again sooner.

But if the heating is required to be on an 90% duty cycle to keep the room at the requested temperature, the
thermostat never achieves this.

Sure, but most do size the heater properly and prefer the lower hysteresis.

So for the sake of a crap thermostat, the answer is to have a
heater capable of heating the room with a 50% duty cycle?

Nope, most care more about hysteresis than they do about
the frequency of switching, so a heater is included with the
better bi metallic thermostats. Some of them allow you to
not connect the heater if you dont want it.

And it isnt just room heater thermostats either, they are seen with cars etc too.

For internal heating or for the engine cooling?

Engine cooling.

Yes, a proper modern electronic thermostat is better again,
and allows other stuff like time of day and day of week variations in the set point etc but thats a different
matter entirely.

They still seem to be selling these bi-metal things, even though an electronic one doesn't cost much more now.

Yeah, you can get some bizarre stuff like that.

The best digital thermostats do cost quite a bit more than
the cheapest bi metallic thermostats from china tho.

The cheapest digital thermostat works perfectly.

Sure, but the cheapest bi metallic strip thermostat is cheaper
again, particularly when its what was there all along and you are
considering replacing it with a proper modern digital thermostat.

And if you care about the cost, you should really be using
a decent modern digital thermostat that includes day and
week time bands too, because that will very quickly pay
for itself in reduced heating costs if you arent prepared to
keep manually fiddling with the thermostat every day etc.

I leave the heating on 24/7. I see little point in letting the house cool when I'm out then having to warm it back
up.

It does save quite a bit on the cost of heating if you are out much.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

Also true of decent proportional control too.

What is one of those?

Proportinal control adjusts the power output of the load rather
than just turning it off or on. So you can have 61%, 62% etc etc etc.

Corse not all loads can do that.

I suppose theoretically a central heating boiler could do this if you could interface the room stat with the water
temp stat.

And that isnt the only way to do that either.

Corse there isnt any point in your case because you dont care about hysteresis.

Most do tho.

Out of interest, how would you do it?

I'd control the whole house with a computer myself and have
it do everything, lights, alarms, heating, cooling everything.

If I wasnt going to do that for some reason like cost I'd use a proper modern
digital thermostat that could be programmed to vary the temps during the day
and by the week if all the days werent the same. With a decent override
system so you could tell it 'I'll be away for half a day from now' etc.

Makes more sense to fully automate everything IMO tho.

On Mon, 05 Mar 2012 23:10:10 -0000, Rod Speed wrote:

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote




Maybe its just a lousy design.

All five of them? Different makes?

I meant what you are controlling with them. I just dont believe
that everyone has the same problem you have finding a bi
metallic strip thermostat that will actually switch the load you
are switching and they all ove to use digital thermostats instead.

Must be the motorized valve is sticking and presenting a very big starting load?

Its gotta be something like that that sees 5 different bi metallic thermostats
arcing instead of switching cleanly.

Unless you somehow managed to end up with 5 completely different ones
with no magnetic contacts that stop arcing which sounds very unlikely indeed.

Sounds like it. Changing the stat to digital fixed it anyway. Easier than changing the valve.

It's never had a problem opening.

Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

The digistat is happy enough

Where did you get its inductive load figure from ?

I didn't. I was guessing that's why it caused the arc.

Actually...... I now remember trying a couple of the stats at one time to run a cooling fan. It's just as 30 watt extractor - much like you'd buy for a kitchen. The same problem occurred with that. Maybe I did have a load of crap stats? They all definitely gave a rating for inductive, so I assume they were designed to handle inductive.

It isnt even possible and the heater isnt a workaround, its a significant design feature which does what its
designed to do, reduce the hysteresis.

It means the thermostat is guessing at the temperature,

No it does not. When used properly, the heater is ONLY on when
the load is on and so there is no guessing what so ever involved.

The ONLY thing the heater does is cause the thermostat to turn
OFF earlier than it would otherwise do without a heater and even
that isnt a guess, its a deliberate choice by the designer to do that.

If it was accurate enough so that the resistor increased the temperature inside the stat by exactly 2 degrees,

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

Well if it's not that accurate, then it's just a guess it's doing.

then it would reduce the hysteresis from 3C to 1C, but I doubt a resistor placed close to a bi-metallic strip is that
accurate. It depends on air movement in the room for a start.

And the room temp too.

And the hysteresis with a bi metallic strip thermostat is essentially
determined by the magnetic contacts that are there to stop arcing,
and those dont have a rigidly specified temperature hysteresis anyway.

That isnt even possible either.

I would not call that a good design.

It is anyway, because the heater reduces the inevitable
hysteresis that you get with a bimetallic strip thermostat.

Why on earth do people feel the need to have such a precise control of temperature anyway?

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

I don't even notice a 4C change. I've seen some people actually put on a jacket to go form a heated house to a heated car, but surely most folk aren't that bad. Has most of society really forgotten how to moderate their own body temperature?

Most people have more than a 1 degree comfort range.

And you dont get that with a bi metallic strip thermostat with no heater.

You get a few degrees. Which is more than 1 :-P

I know someone else who feels the cold and not the heat like you - they said they have a vitamin D deficiency and
anaemia.

Interesting you should say that. A mate of mine who is rather
younger than me has just discovered that he has a vitamin D
deficiency when he got a blood test for something else entirely.
Unfortunately I get the form for my annual blood test at the GP
consultation the year before I actually get the test, so the GP
has the results of the test when I show up for the annual consult
so I couldnt get a vitamin D test included in my blood test. I will
do so next time, because he is outside quite a bit and he shouldnt
have a vitamin D deficiency in theory.

But I definitely an not anaemic.

I'll settle for wimp then.

And I have always been like that temperature wise even as a kid.

I'm sure you could train yourself to become accustomed to it.

Sure, but there isnt any point in doing that, I prefer to be comfortable instead.

And its no big deal to put a top on over the T shirt before anyone else does.

It's a lot more convenient not to have to adjust clothing. I don't care what I'm wearing, I can just go out in whatever. I don't have to take anything with me.

And I save power in summer when I put the cooler on well after everyone else does.

That problem does not exist in the UK.

The house was designed passive solar so I bask in the sun on sunny
days in winter and everyone who visits comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

So you won't even have a room stat for heating?

Sure, but most do size the heater properly and prefer the lower hysteresis.

So for the sake of a crap thermostat, the answer is to have a
heater capable of heating the room with a 50% duty cycle?

Nope, most care more about hysteresis than they do about
the frequency of switching, so a heater is included with the
better bi metallic thermostats. Some of them allow you to
not connect the heater if you dont want it.

And it isnt just room heater thermostats either, they are seen with cars etc too.

For internal heating or for the engine cooling?

Engine cooling.

Why would engine cooling require anything more accurate then 4C hysteresis?

Yeah, you can get some bizarre stuff like that.

The best digital thermostats do cost quite a bit more than
the cheapest bi metallic thermostats from china tho.

The cheapest digital thermostat works perfectly.

Sure, but the cheapest bi metallic strip thermostat is cheaper
again, particularly when its what was there all along and you are
considering replacing it with a proper modern digital thermostat.

And if you care about the cost, you should really be using
a decent modern digital thermostat that includes day and
week time bands too, because that will very quickly pay
for itself in reduced heating costs if you arent prepared to
keep manually fiddling with the thermostat every day etc.

I leave the heating on 24/7. I see little point in letting the house cool when I'm out then having to warm it back
up.

It does save quite a bit on the cost of heating if you are out much.

If I go away for a day (as in come back the next day) or more, I'll either switch it off or change the stat to frost protection. But just out for 8 hours, no.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

I don't prefer a different temperature during the day and at night. If I did it would be a nuisance, because I'd have to cool the house instantly to the night time temperature before going to bed, then warm it up instantly in the morning.

Proportinal control adjusts the power output of the load rather
than just turning it off or on. So you can have 61%, 62% etc etc etc.

Corse not all loads can do that.

I suppose theoretically a central heating boiler could do this if you could interface the room stat with the water
temp stat.

And that isnt the only way to do that either.

Corse there isnt any point in your case because you dont care about hysteresis.

Most do tho.

Out of interest, how would you do it?

I'd control the whole house with a computer myself and have
it do everything, lights, alarms, heating, cooling everything.

If I wasnt going to do that for some reason like cost I'd use a proper modern
digital thermostat that could be programmed to vary the temps during the day
and by the week if all the days werent the same. With a decent override
system so you could tell it 'I'll be away for half a day from now' etc.

Makes more sense to fully automate everything IMO tho.

More fun too :-)

--
http://petersparrots.com
http://petersphotos.com

Confucius say man who sniff coke, drown.

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote

Maybe its just a lousy design.

All five of them? Different makes?

I meant what you are controlling with them. I just dont believe
that everyone has the same problem you have finding a bi
metallic strip thermostat that will actually switch the load you
are switching and they all ove to use digital thermostats instead.

Must be the motorized valve is sticking and presenting a very big starting load?

Its gotta be something like that that sees 5 different bi metallic thermostats arcing instead of switching cleanly.

Unless you somehow managed to end up with 5 completely different ones
with no magnetic contacts that stop arcing which sounds very unlikely indeed.

Sounds like it. Changing the stat to digital fixed it anyway. Easier than changing the valve.

It's never had a problem opening.

Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

The digistat is happy enough

Sure, but its likely to have been designed to handle motorised valves.

Where did you get its inductive load figure from ?

I didn't. I was guessing that's why it caused the arc.

Actually...... I now remember trying a couple of the stats at one
time to run a cooling fan. It's just as 30 watt extractor - much
like you'd buy for a kitchen. The same problem occurred with that. Maybe I did have a load of crap stats? They all
definitely gave a
rating for inductive, so I assume they were designed to handle inductive.

Bet you'll find if you actually compare the inductive
load with the rating that both exceed it by quite a bit.

It isnt even possible and the heater isnt a workaround, its a
significant design feature which does what its designed to do,
reduce the hysteresis.

It means the thermostat is guessing at the temperature,

No it does not. When used properly, the heater is ONLY on when
the load is on and so there is no guessing what so ever involved.

The ONLY thing the heater does is cause the thermostat to turn
OFF earlier than it would otherwise do without a heater and even
that isnt a guess, its a deliberate choice by the designer to do that.

If it was accurate enough so that the resistor increased the
temperature inside the stat by exactly 2 degrees,

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

Well if it's not that accurate, then it's just a guess it's doing.

Nope, its not even attempting to do anything about measuring
or estimating temperature, its JUST heating the strip so that
it opens quicker than it would otherwise do without a heater.

No guessing what so ever involved at all.

then it would reduce the hysteresis from 3C to 1C, but I doubt a resistor placed close to a bi-metallic strip is
that accurate. It depends on air movement in the room for a start.

And the room temp too.

And the hysteresis with a bi metallic strip thermostat is essentially
determined by the magnetic contacts that are there to stop arcing,
and those dont have a rigidly specified temperature hysteresis anyway.

That isnt even possible either.

I would not call that a good design.

It is anyway, because the heater reduces the inevitable
hysteresis that you get with a bimetallic strip thermostat.

Why on earth do people feel the need to have such a precise control of temperature anyway?

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

I don't even notice a 4C change.

I do.

I've seen some people actually put on a jacket to go form a heated house to a heated car,

I would if I am wearing just a T shirt in the heated house.

I actually take my fleece that I wear over a sweat over the T shirt
in winter when I go out in all but the most extreme weather. I leave
the fleece on in the most extreme weather and when doing the
garage/yard sale run in the depths of winter because the regulars
often stand around talking waiting for somewhere to open and that
can be damned cold, particularly with a heavy frost.

The regulars show up an hour before the advertised opening time.

but surely most folk aren't that bad. Has most of society really forgotten how to moderate their own body
temperature?

Most choose to do what is most comfortable, including me.

When I go out for exercise, I try to anticipate what I will be wearing
at the end of the very long walk, because it irritates me to have to
have removed the sweat because the movement has warmed me up
and the air has warmed up. I normally start at first light, when its just
light enough so I dont trip over stuff. I dont walk around the streets,
too boring, I normally walk in the bush/scrub areas on the hills at the
back of town for 1:30-2 hours.

Most people have more than a 1 degree comfort range.

And you dont get that with a bi metallic strip thermostat with no heater.

You get a few degrees. Which is more than 1 :-P

Its more than most's preferred comfort range which is
why heaters in bi metallic thermostats were invented.

The wouldnt bother with an extra cost item like that if
most dont prefer the reduced hysteresis that produces.

I know someone else who feels the cold and not the heat like you - they said they have a vitamin D deficiency and
anaemia.

Interesting you should say that. A mate of mine who is rather
younger than me has just discovered that he has a vitamin D
deficiency when he got a blood test for something else entirely.
Unfortunately I get the form for my annual blood test at the GP
consultation the year before I actually get the test, so the GP
has the results of the test when I show up for the annual consult
so I couldnt get a vitamin D test included in my blood test. I will
do so next time, because he is outside quite a bit and he shouldnt
have a vitamin D deficiency in theory.

But I definitely an not anaemic.

I'll settle for wimp then.

That wont fly either with the hot weather.

We routinely have 10 days over 40C,

If you lot got that much you'd be dying like flys.

And I have always been like that temperature wise even as a kid.

I'm sure you could train yourself to become accustomed to it.

Sure, but there isnt any point in doing that, I prefer to be comfortable instead.

And its no big deal to put a top on over the T shirt before anyone else does.

It's a lot more convenient not to have to adjust clothing. I don't care what I'm wearing, I can just go out in
whatever. I don't have to take anything with me.

One of the garage/yard salers wears shorts the entire year.

We routinely get heavy frosts at -10C and we are out at that time, in the dark.

No one else is that silly.

And I save power in summer when I put the cooler on well after everyone else does.

That problem does not exist in the UK.

The house was designed passive solar so I bask in the sun on sunny
days in winter and everyone who visits comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

So you won't even have a room stat for heating?

I do, but dont use it anymore.

Sure, but most do size the heater properly and prefer the lower hysteresis.

So for the sake of a crap thermostat, the answer is to have a
heater capable of heating the room with a 50% duty cycle?

Nope, most care more about hysteresis than they do about
the frequency of switching, so a heater is included with the
better bi metallic thermostats. Some of them allow you to
not connect the heater if you dont want it.

And it isnt just room heater thermostats either, they are seen with cars etc too.

For internal heating or for the engine cooling?

Engine cooling.

Why would engine cooling require anything more accurate then 4C hysteresis?

No idea. I just noticed that when I was trying to find an decent summary
of why bi metallic thermostats normally have a heater, on the web.

Yeah, you can get some bizarre stuff like that.

The best digital thermostats do cost quite a bit more than the cheapest bi metallic thermostats from china tho.

The cheapest digital thermostat works perfectly.

Sure, but the cheapest bi metallic strip thermostat is cheaper
again, particularly when its what was there all along and you are
considering replacing it with a proper modern digital thermostat.

And if you care about the cost, you should really be using
a decent modern digital thermostat that includes day and
week time bands too, because that will very quickly pay
for itself in reduced heating costs if you arent prepared to
keep manually fiddling with the thermostat every day etc.

I leave the heating on 24/7. I see little point in letting the
house cool when I'm out then having to warm it back up.

It does save quite a bit on the cost of heating if you are out much.

If I go away for a day (as in come back the next day) or more, I'll either switch it off or change the stat to frost
protection. But just out for 8 hours, no.

You'd reduce your heating costs quite a bit if you did.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

I don't prefer a different temperature during the day and at night. If I did it would be a nuisance, because I'd have
to cool the house
instantly to the night time temperature before going to bed, then
warm it up instantly in the morning.

There is no need for any instantly, modern digital thermostats
anticipate the setpoint, now how long it takes to move between
the setpoints and just stop heating at the appropriate time at bed
time and start heating before the daytime setpoint in the morning
so when you get up, its at the temp you say you want.

Proportinal control adjusts the power output of the load rather than just turning it off or on. So you can have
61%, 62% etc etc etc.

Corse not all loads can do that.

I suppose theoretically a central heating boiler could do this if you could interface the room stat with the water
temp stat.

And that isnt the only way to do that either.

Corse there isnt any point in your case because you dont care about hysteresis.

Most do tho.

Out of interest, how would you do it?

I'd control the whole house with a computer myself and have
it do everything, lights, alarms, heating, cooling everything.

If I wasnt going to do that for some reason like cost I'd use a
proper modern digital thermostat that could be programmed to vary the temps during the day and by the week if all the
days werent the same. With a decent override system so you could tell it 'I'll be away for half a day from now' etc.

Makes more sense to fully automate everything IMO tho.

More fun too :-)

True.

I did the control system for a fancy solar greenhouse at work.

Used a massive great solar air heater that heated up quite literally
a big room fool of road gravel during the day and that was used to
keep warm the greenhouse at night when there was no solar.

And another with fancy automated curtains and a fancy heat recovery system too.

Not that practical for a domestic situation tho, most would prefer to actually
be able to occupy the room that would otherwise be full of road metal.

Brian Gaff wrote
A.Lee wrote
DerekG wrote

It's a bit like trying to throw a Yo-Yo away whilst still holding onto the string. And yes it's a crap plumbers
idea.

It isnt. I've been on a training course that shows the graphs of heat and gas used. The heated stats use less gas,
and keep the room at a steadier temperature than the standard on/off stats.

That though depends on the site of the stat, and how well designed the placement of the radiators were in the first
place.

Nope, you always get a benefit.

The only real downside is that the system switches more.

On Tue, 06 Mar 2012 01:00:30 -0000, Rod Speed wrote:

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
It's never had a problem opening.

Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

The digistat is happy enough

Sure, but its likely to have been designed to handle motorised valves.

Shouldn't any stat handle one? It's not like it's a BIG load, although it's inductive, but they should be able to handle that?

Where did you get its inductive load figure from ?

I didn't. I was guessing that's why it caused the arc.

Actually...... I now remember trying a couple of the stats at one
time to run a cooling fan. It's just as 30 watt extractor - much
like you'd buy for a kitchen. The same problem occurred with that. Maybe I did have a load of crap stats? They all
definitely gave a
rating for inductive, so I assume they were designed to handle inductive.

Bet you'll find if you actually compare the inductive
load with the rating that both exceed it by quite a bit.

The inductive rating I remember as being a couple of amps. It was not a 480 watt fan. It was 30 watts.

No it does not. When used properly, the heater is ONLY on when
the load is on and so there is no guessing what so ever involved.

The ONLY thing the heater does is cause the thermostat to turn
OFF earlier than it would otherwise do without a heater and even
that isnt a guess, its a deliberate choice by the designer to do that.

If it was accurate enough so that the resistor increased the
temperature inside the stat by exactly 2 degrees,

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

Well if it's not that accurate, then it's just a guess it's doing.

Nope, its not even attempting to do anything about measuring
or estimating temperature, its JUST heating the strip so that
it opens quicker than it would otherwise do without a heater.

No guessing what so ever involved at all.

It's the equivalent of a guess - yes I know it doesn't have the ability to "think", but it's not measuring the room temperature directly, it's measuring the combination of the room temperature and the output of the resistor.

It is anyway, because the heater reduces the inevitable
hysteresis that you get with a bimetallic strip thermostat.

Why on earth do people feel the need to have such a precise control of temperature anyway?

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

I don't even notice a 4C change.

I do.

You said you don't mind it being really warm though. So presumably varying from your minimum comfortable temperature to 4C higher wouldn't bother you?

I've seen some people actually put on a jacket to go form a heated house to a heated car,

I would if I am wearing just a T shirt in the heated house.

Even if it's only for a minute? Surely the specific heat capacity of your body causes you to take a while to cool down.

I actually take my fleece that I wear over a sweat over the T shirt
in winter when I go out in all but the most extreme weather. I leave
the fleece on in the most extreme weather and when doing the
garage/yard sale run in the depths of winter because the regulars
often stand around talking waiting for somewhere to open and that
can be damned cold, particularly with a heavy frost.

http://i0.kym-cdn.com/entries/icons/...4/facepalm.jpg

but surely most folk aren't that bad. Has most of society really forgotten how to moderate their own body
temperature?

Most choose to do what is most comfortable, including me.

The trouble is people are becoming worse. In a few more generations, we'll be wanting thermostats with a 0.1C accuracy, and we simply won't be able to go outside at all.

When I go out for exercise, I try to anticipate what I will be wearing
at the end of the very long walk, because it irritates me to have to
have removed the sweat because the movement has warmed me up
and the air has warmed up. I normally start at first light, when its just
light enough so I dont trip over stuff. I dont walk around the streets,
too boring, I normally walk in the bush/scrub areas on the hills at the
back of town for 1:30-2 hours.

I don't have to do that anticipation :-P

Most people have more than a 1 degree comfort range.

And you dont get that with a bi metallic strip thermostat with no heater.

You get a few degrees. Which is more than 1 :-P

Its more than most's preferred comfort range which is
why heaters in bi metallic thermostats were invented.

The wouldnt bother with an extra cost item like that if
most dont prefer the reduced hysteresis that produces.

I doubt a resistor costs that much. It's probably more that un-knowledgable people will think they're faulty if they have a 4C hysteresis and be liable to send them back.

Interesting you should say that. A mate of mine who is rather
younger than me has just discovered that he has a vitamin D
deficiency when he got a blood test for something else entirely.
Unfortunately I get the form for my annual blood test at the GP
consultation the year before I actually get the test, so the GP
has the results of the test when I show up for the annual consult
so I couldnt get a vitamin D test included in my blood test. I will
do so next time, because he is outside quite a bit and he shouldnt
have a vitamin D deficiency in theory.

But I definitely an not anaemic.

I'll settle for wimp then.

That wont fly either with the hot weather.

We routinely have 10 days over 40C,

If you lot got that much you'd be dying like flys.

I went to the South of France when they had that heatwave that killed hundreds of people. It didn't bother me. I became accustomed to it within a couple of days.

And I have always been like that temperature wise even as a kid.

I'm sure you could train yourself to become accustomed to it.

Sure, but there isnt any point in doing that, I prefer to be comfortable instead.

And its no big deal to put a top on over the T shirt before anyone else does.

It's a lot more convenient not to have to adjust clothing. I don't care what I'm wearing, I can just go out in
whatever. I don't have to take anything with me.

One of the garage/yard salers wears shorts the entire year.

We routinely get heavy frosts at -10C and we are out at that time, in the dark.

No one else is that silly.

There are a few sensible people around. Wait till there's an ice age, then only people like him and me will survive.

The house was designed passive solar so I bask in the sun on sunny
days in winter and everyone who visits comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

So you won't even have a room stat for heating?

I do, but dont use it anymore.

Don't you get some winters with a week of no sun? Or does Australia have considerably less cloud than us? That's what I hate about the UK, cloud. Rain is fine, sun is fine, but cloudy all the time is boring.

Nope, most care more about hysteresis than they do about
the frequency of switching, so a heater is included with the
better bi metallic thermostats. Some of them allow you to
not connect the heater if you dont want it.

And it isnt just room heater thermostats either, they are seen with cars etc too.

For internal heating or for the engine cooling?

Engine cooling.

Why would engine cooling require anything more accurate then 4C hysteresis?

No idea. I just noticed that when I was trying to find an decent summary
of why bi metallic thermostats normally have a heater, on the web.

My Golf (1998 model) does seem to keep PRECISELY at 90C on the guage. Older vehicles never used to do that. Maybe it makes the engine more efficient, or produce less pollution, or last a bit longer?

Sure, but the cheapest bi metallic strip thermostat is cheaper
again, particularly when its what was there all along and you are
considering replacing it with a proper modern digital thermostat.

And if you care about the cost, you should really be using
a decent modern digital thermostat that includes day and
week time bands too, because that will very quickly pay
for itself in reduced heating costs if you arent prepared to
keep manually fiddling with the thermostat every day etc.

I leave the heating on 24/7. I see little point in letting the
house cool when I'm out then having to warm it back up.

It does save quite a bit on the cost of heating if you are out much.

If I go away for a day (as in come back the next day) or more, I'll either switch it off or change the stat to frost
protection. But just out for 8 hours, no.

You'd reduce your heating costs quite a bit if you did.

I don't believe it would be that much. After all when I come back it has to warm the house back up.

I can believe you for longer periods when the house cools enough so that it's no longer losing significant heat to the outside (like when I'm away for 24 hours or more), and I do turn the heating off or down then anyway.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

I don't prefer a different temperature during the day and at night. If I did it would be a nuisance, because I'd have
to cool the house
instantly to the night time temperature before going to bed, then
warm it up instantly in the morning.

There is no need for any instantly, modern digital thermostats
anticipate the setpoint, now how long it takes to move between
the setpoints and just stop heating at the appropriate time at bed
time and start heating before the daytime setpoint in the morning
so when you get up, its at the temp you say you want.

That would be fine if you got up at an exact time every day. Although it would still be a problem - either the house is cooling down before your bedtime, or you are going to bed with the house too warm.

--
http://petersparrots.com
http://petersphotos.com

A weekend wasted is not a wasted weekend.

On Mar 6, 3:29*am, "Rod Speed" wrote:
Brian Gaff wrote

A.Lee wrote
DerekG wrote
It's a bit like trying to throw a Yo-Yo away whilst still holding onto the string. And yes it's a crap plumbers
idea.
It isnt. I've been on a training course that shows the graphs of heat and gas used. The heated stats use less gas,
and keep the room at a steadier temperature than the standard on/off stats.
That though depends on the *site of the stat, and how well designed the placement of the radiators were in the first
place.

Nope, you always get a benefit.

The only real downside is that the system switches more.

and doesn't warm up from cold so fast.

Robert

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
It's never had a problem opening.

Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

The digistat is happy enough

Sure, but its likely to have been designed to handle motorised valves.

Shouldn't any stat handle one?

Not if it hasnt got magnetised contacts to provide a snap action.

It's not like it's a BIG load, although it's inductive, but they should be able to handle that?

Not if it hasnt got magnetised contacts to provide a snap action.

You did say that at least one of yours doesnt.

Where did you get its inductive load figure from ?

I didn't. I was guessing that's why it caused the arc.

Actually...... I now remember trying a couple of the stats at one
time to run a cooling fan. It's just as 30 watt extractor - much
like you'd buy for a kitchen. The same problem occurred with that.
Maybe I did have a load of crap stats? They all definitely gave a
rating for inductive, so I assume they were designed to handle inductive.

Bet you'll find if you actually compare the inductive
load with the rating that both exceed it by quite a bit.

The inductive rating I remember as being a couple of amps. It was not a 480 watt fan. It was 30 watts.

You cant jjust use the amps with inductive loads.

No it does not. When used properly, the heater is ONLY on when
the load is on and so there is no guessing what so ever involved.

The ONLY thing the heater does is cause the thermostat to turn
OFF earlier than it would otherwise do without a heater and even
that isnt a guess, its a deliberate choice by the designer to do that.

If it was accurate enough so that the resistor increased the
temperature inside the stat by exactly 2 degrees,

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

Well if it's not that accurate, then it's just a guess it's doing.

Nope, its not even attempting to do anything about measuring
or estimating temperature, its JUST heating the strip so that
it opens quicker than it would otherwise do without a heater.

No guessing what so ever involved at all.

It's the equivalent of a guess

Nope, nothing like it. Something else entirely.

- yes I know it doesn't have the ability to "think", but it's not measuring the room temperature directly,

Yes it is when it turns ON when the heater is off.

it's measuring the combination of the room temperature and the output of the resistor.

Nope, not when the it turns on and the heater is off.

It doesnt do that when turning off either, when its turning
off, it isnt even using the air temp at all, the heater just
turns it off well before it would otherwise turn off to
significantly reduce the hysteresis.

THEN it measures the air temp again, with the resistor off.

It is anyway, because the heater reduces the inevitable
hysteresis that you get with a bimetallic strip thermostat.

Why on earth do people feel the need to have such a precise control of temperature anyway?

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

I don't even notice a 4C change.

I do.

You said you don't mind it being really warm though.

Thats a different effect to when its say 20C

So presumably varying from your minimum comfortable temperature to 4C higher wouldn't bother you?

It does bother me when its 4C colder than I prefer.

I've seen some people actually put on a jacket to go form a heated house to a heated car,

I would if I am wearing just a T shirt in the heated house.

Even if it's only for a minute?

Yep, because its a lot more than a minute in total
for the whole trip when going out shopping etc.

Surely the specific heat capacity of your body causes you to take a while to cool down.

Your core temp doesnt change. You feel the cold when
your skin temp drops significantly unless you are like that
mate of mine that wears shorts right thru the entire winter.

Another one doesnt go quite that far, but doesnt wear
much on top. He's pretty fat tho and I keep reminding him
that its his fat that keeps him warm, its a built in jacket.

Even he does wear a top when we are standing
around in the dark with a heavy frost at -10C for
an hour so outside with a decent wind.

The one who wears shorts right thru the winter doesnt show up that early.

I used to ride to school on a bike when I was a kid and in the depths
of winter, my ears felt like they might freeze off after the long downhill
run. I wasnt stupid enough to do that wearing just a T shirt and shorts.

I actually take pff my fleece that I wear over a sweat over the T shirt in winter when I go out in all but the most
extreme weather. I leave the fleece on in the most extreme weather and when doing the garage/yard sale run in the
depths of winter because the regulars often stand around talking waiting for somewhere to open and that can be damned
cold, particularly with a heavy frost.

http://i0.kym-cdn.com/entries/icons/...4/facepalm.jpg

Stop crying boy, you some sort of bald sook ?

but surely most folk aren't that bad. Has most of society really
forgotten how to moderate their own body temperature?

Most choose to do what is most comfortable, including me.

The trouble is people are becoming worse.

The damned ancient greeks used to sit around in
their togas or whatever they wore and howl like that.

In a few more generations, we'll be wanting thermostats with a 0.1C accuracy, and we simply won't be able to go
outside at all.

We used to drive around in unheated cars in the
depth of winter and now arent that stupid anymore.

That change didnt actually produce the end
of civilisation as we know it for some reason.

Locally, no one did anything much special during the inevitable
10 days over 40C that happens many years. Now almost
everyone has at least an evaporative cooler, what the yanks
call a swamp cooler, and many have full airconditioning.

I can remember one car trip in conditions like that in a car
with no airconditioning at all. It was so ****ing hot that we
pulled up at a river and just jumped in the water and stayed
there in the shade in the water until the sun started to go down.

When I go out for exercise, I try to anticipate what I will be wearing at the end of the very long walk, because it
irritates me to have to have removed the sweat because the movement has warmed me up and the air has warmed up. I
normally start at first light, when its just light enough so I dont trip over stuff. I dont walk around the streets,
too boring, I normally walk in the bush/scrub areas on the hills at the back of town for 1:30-2 hours.

I don't have to do that anticipation :-P

And arent as comfortable as me.

Most people have more than a 1 degree comfort range.

And you dont get that with a bi metallic strip thermostat with no heater.

You get a few degrees. Which is more than 1 :-P

Its more than most's preferred comfort range which is
why heaters in bi metallic thermostats were invented.

The wouldnt bother with an extra cost item like that if
most dont prefer the reduced hysteresis that produces.

I doubt a resistor costs that much.

Still cost more than not having it.

It's probably more that un-knowledgable people will think they're faulty if they have a 4C hysteresis and be liable to
send them back.

Nope. Most prefer a lower hysteresis when it can be achieved that cheaply.

Interesting you should say that. A mate of mine who is rather
younger than me has just discovered that he has a vitamin D
deficiency when he got a blood test for something else entirely.
Unfortunately I get the form for my annual blood test at the GP
consultation the year before I actually get the test, so the GP
has the results of the test when I show up for the annual consult
so I couldnt get a vitamin D test included in my blood test. Iwill do so next time, because he is outside quite a
bit and he
shouldnt have a vitamin D deficiency in theory.

But I definitely an not anaemic.

I'll settle for wimp then.

That wont fly either with the hot weather.

We routinely have 10 days over 40C,

If you lot got that much you'd be dying like flys.

I went to the South of France when they had that heatwave that killed hundreds of people. It didn't bother me. I
became accustomed to it within a couple of days.

You'd be dead if you tried digging ditches in ours.

And I have always been like that temperature wise even as a kid.

I'm sure you could train yourself to become accustomed to it.

Sure, but there isnt any point in doing that, I prefer to be comfortable instead.

And its no big deal to put a top on over the T shirt before anyone else does.

It's a lot more convenient not to have to adjust clothing. I don't care what I'm wearing, I can just go out in
whatever. I don't have to take anything with me.

One of the garage/yard salers wears shorts the entire year.

We routinely get heavy frosts at -10C and we are out at that time, in the dark.

No one else is that silly.

There are a few sensible people around. Wait till there's an ice age, then only people like him and me will survive.

I'll be basking in the sun in my passive solar house pointing
at your frozen corpse in the snow drift and laughing.

And we wont bother to bury you either, bugger that. Let the wolves eat your corpse instead.

The house was designed passive solar so I bask in the sun on sunny
days in winter and everyone who visits comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

So you won't even have a room stat for heating?

I do, but dont use it anymore.

Don't you get some winters with a week of no sun?

Almost never, maybe once in 20 years.

Or does Australia have considerably less cloud than us?

Yep.

That's what I hate about the UK, cloud. Rain is fine, sun is fine, but cloudy all the time is boring.

Yeah, even a very heavy frost is quite pleasant when its
sunny, particularly when I'm basking in it in my passive
solar house looking out over the oval of the school thats
quite close with the entire area bright white from the frost.

We dont get snow here.

Nope, most care more about hysteresis than they do about the frequency of switching, so a heater is included with
the better bi metallic thermostats. Some of them allow you to not connect the heater if you dont want it.

And it isnt just room heater thermostats either, they are seen with cars etc too.

For internal heating or for the engine cooling?

Engine cooling.

Why would engine cooling require anything more accurate then 4C hysteresis?

No idea. I just noticed that when I was trying to find an decent summary of why bi metallic thermostats normally have
a heater, on the web.

My Golf (1998 model) does seem to keep PRECISELY at 90C on the guage. Older vehicles never used to do that. Maybe it
makes the engine more efficient, or produce less pollution,

Yeah, likely, I meant to say that and forgot to say it.

How do you find the Golf ? My previous was a 72, lasted 35+ years
until I was stupid enought to not bother to fix the windscreen leak that
I kinew produced a wet floor when it rained much until that eventually
rusted a hole in the floor and was no longer registerable and not
economic to repair.

The yanks howl about bits falling off their modern Golfs, but it isnt
clear if thats just because they are mostly made in Mexico of if VW
has gone down hill significantly since they did mine. I only ever had
to replace a distributor rotor, an alternator regulator and a couple
of other very minor things in those 35+ years.

or last a bit longer?

Mine lasted 35+ years fine without that and didnt die because of that either.

Sure, but the cheapest bi metallic strip thermostat is cheaper
again, particularly when its what was there all along and you are
considering replacing it with a proper modern digital thermostat.

And if you care about the cost, you should really be using
a decent modern digital thermostat that includes day and
week time bands too, because that will very quickly pay
for itself in reduced heating costs if you arent prepared to
keep manually fiddling with the thermostat every day etc.

I leave the heating on 24/7. I see little point in letting the
house cool when I'm out then having to warm it back up.

It does save quite a bit on the cost of heating if you are out much.

If I go away for a day (as in come back the next day) or more, I'll either switch it off or change the stat to frost
protection. But just out for 8 hours, no.

You'd reduce your heating costs quite a bit if you did.

I don't believe it would be that much. After all when I come back it has to warm the house back up.

Thats another very common misapprehension. Its just
basic physics that you lose significantly less at the house
lower temps, because loss is entirely determined by the
temperature differential all other factors kept constant.

The only time it gets more complicated is if you are using
a heat pump to heat the house and it uses an external air
heat exchanger that can freeze up if its not sized right for
the higher heat pumping required for the change from night
to day set point with the outside air temp below freezing.

I can believe you for longer periods when the house cools enough so that it's no longer losing significant heat to the
outside (like when I'm away for 24 hours or more),

Its just as true for the 8 hours or so you are in bed etc too.

And plenty are out for 8 hours or more at work every day too.

So many only have 8 hours out of 24 where they need the higher setpoint.

and I do turn the heating off or down then anyway.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

I don't prefer a different temperature during the day and at night. If I did it would be a nuisance, because I'd
have to cool the house instantly to the night time temperature before going to bed, then warm it up instantly in the
morning.

There is no need for any instantly, modern digital thermostats
anticipate the setpoint, now how long it takes to move between
the setpoints and just stop heating at the appropriate time at bed
time and start heating before the daytime setpoint in the morning
so when you get up, its at the temp you say you want.

That would be fine if you got up at an exact time every day.

Doesnt have to be exactly. If you set it for the earliest
time you normally get up, you still save significantly.

Although it would still be a problem - either the house is cooling down before your bedtime,

Nope, it just stops heating then.

or you are going to bed with the house too warm.

Not if you have enough of a clue to have a different zone temp
for the bedroom from wherever you are before you go to bed.

Taint rocket science.

On Tue, 06 Mar 2012 17:52:01 -0000, Rod Speed wrote:

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote


Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

The digistat is happy enough

Sure, but its likely to have been designed to handle motorised valves.

Shouldn't any stat handle one?

Not if it hasnt got magnetised contacts to provide a snap action.

Presumably then it shouldn't have a rating for inductive load? I'm sure it did.

It's not like it's a BIG load, although it's inductive, but they should be able to handle that?

Not if it hasnt got magnetised contacts to provide a snap action.

You did say that at least one of yours doesnt.

I said maybe that's the problem with them. I haven't looked closely enough to see if they have magnets.

Where did you get its inductive load figure from ?

I didn't. I was guessing that's why it caused the arc.

Actually...... I now remember trying a couple of the stats at one
time to run a cooling fan. It's just as 30 watt extractor - much
like you'd buy for a kitchen. The same problem occurred with that.
Maybe I did have a load of crap stats? They all definitely gave a
rating for inductive, so I assume they were designed to handle inductive.

Bet you'll find if you actually compare the inductive
load with the rating that both exceed it by quite a bit.

The inductive rating I remember as being a couple of amps. It was not a 480 watt fan. It was 30 watts.

You cant jjust use the amps with inductive loads.

Then why do they state them?

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

Well if it's not that accurate, then it's just a guess it's doing.

Nope, its not even attempting to do anything about measuring
or estimating temperature, its JUST heating the strip so that
it opens quicker than it would otherwise do without a heater.

No guessing what so ever involved at all.

It's the equivalent of a guess

Nope, nothing like it. Something else entirely.

- yes I know it doesn't have the ability to "think", but it's not measuring the room temperature directly,

Yes it is when it turns ON when the heater is off.

it's measuring the combination of the room temperature and the output of the resistor.

Nope, not when the it turns on and the heater is off.

It doesnt do that when turning off either, when its turning
off, it isnt even using the air temp at all, the heater just
turns it off well before it would otherwise turn off to
significantly reduce the hysteresis.

THEN it measures the air temp again, with the resistor off.

Exactly. It's turning off when it shouldn't, therefore the heater is not on as long as it needs to be to keep the room warm.

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

I don't even notice a 4C change.

I do.

You said you don't mind it being really warm though.

Thats a different effect to when its say 20C

So presumably varying from your minimum comfortable temperature to 4C higher wouldn't bother you?

It does bother me when its 4C colder than I prefer.

Why not set your room temperature so that you aren't near the minimum of your comfort zone? As I said most people have a zone of comfort, not one precise temperature. There is no need for great accuracy in room temperatures.

I've seen some people actually put on a jacket to go form a heated house to a heated car,

I would if I am wearing just a T shirt in the heated house.

Even if it's only for a minute?

Yep, because its a lot more than a minute in total
for the whole trip when going out shopping etc.

But most of the time you are in a heated car or a heated shop.

Surely the specific heat capacity of your body causes you to take a while to cool down.

Your core temp doesnt change. You feel the cold when
your skin temp drops significantly unless you are like that
mate of mine that wears shorts right thru the entire winter.

Your skin temp is irrelevant.

Another one doesnt go quite that far, but doesnt wear
much on top. He's pretty fat tho and I keep reminding him
that its his fat that keeps him warm, its a built in jacket.

I find fat people usually feel the cold more, as they are fat due to a low metabolism. Unless of course they're just greedy buggers.

Even he does wear a top when we are standing
around in the dark with a heavy frost at -10C for
an hour so outside with a decent wind.

The one who wears shorts right thru the winter doesnt show up that early.

I used to ride to school on a bike when I was a kid and in the depths
of winter, my ears felt like they might freeze off after the long downhill
run. I wasnt stupid enough to do that wearing just a T shirt and shorts.

That'll be why you're not used to it then. Kids these days are wrapped in cotton wool, so when they get to adulthood, they're wimps.

I actually take pff my fleece that I wear over a sweat over the T shirt in winter when I go out in all but the most
extreme weather. I leave the fleece on in the most extreme weather and when doing the garage/yard sale run in the
depths of winter because the regulars often stand around talking waiting for somewhere to open and that can be damned
cold, particularly with a heavy frost.

http://i0.kym-cdn.com/entries/icons/...4/facepalm.jpg

Stop crying boy, you some sort of bald sook ?

That was not a cry, that was a "facepalm".

but surely most folk aren't that bad. Has most of society really
forgotten how to moderate their own body temperature?

Most choose to do what is most comfortable, including me.

The trouble is people are becoming worse.

The damned ancient greeks used to sit around in
their togas or whatever they wore and howl like that.

What?

In a few more generations, we'll be wanting thermostats with a 0.1C accuracy, and we simply won't be able to go
outside at all.

We used to drive around in unheated cars in the
depth of winter and now arent that stupid anymore.

That change didnt actually produce the end
of civilisation as we know it for some reason.

It was unnecessary (apart from increasing driving visibility). We are getting more and more expensive ways of being comfortable, and more and more things we won't have but are used to when they fail.

Locally, no one did anything much special during the inevitable
10 days over 40C that happens many years. Now almost
everyone has at least an evaporative cooler, what the yanks
call a swamp cooler, and many have full airconditioning.

I can remember one car trip in conditions like that in a car
with no airconditioning at all. It was so ****ing hot that we
pulled up at a river and just jumped in the water and stayed
there in the shade in the water until the sun started to go down.

In those temps, wearing more clothes can be useful, with regular soakings of water. Lots of evaporation.

When I go out for exercise, I try to anticipate what I will be wearing at the end of the very long walk, because it
irritates me to have to have removed the sweat because the movement has warmed me up and the air has warmed up. I
normally start at first light, when its just light enough so I dont trip over stuff. I dont walk around the streets,
too boring, I normally walk in the bush/scrub areas on the hills at the back of town for 1:30-2 hours.

I don't have to do that anticipation :-P

And arent as comfortable as me.

I don't notice the temperature.

And you dont get that with a bi metallic strip thermostat with no heater.

You get a few degrees. Which is more than 1 :-P

Its more than most's preferred comfort range which is
why heaters in bi metallic thermostats were invented.

The wouldnt bother with an extra cost item like that if
most dont prefer the reduced hysteresis that produces.

I doubt a resistor costs that much.

Still cost more than not having it.

It's probably more that un-knowledgable people will think they're faulty if they have a 4C hysteresis and be liable to
send them back.

Nope. Most prefer a lower hysteresis when it can be achieved that cheaply.

But I disagree on WHY they want it.

But I definitely an not anaemic.

I'll settle for wimp then.

That wont fly either with the hot weather.

We routinely have 10 days over 40C,

If you lot got that much you'd be dying like flys.

I went to the South of France when they had that heatwave that killed hundreds of people. It didn't bother me. I
became accustomed to it within a couple of days.

You'd be dead if you tried digging ditches in ours.

I'd get used to it. As long as I was permitted to take my shirt off that is. And some drinks!

Sure, but there isnt any point in doing that, I prefer to be comfortable instead.

And its no big deal to put a top on over the T shirt before anyone else does.

It's a lot more convenient not to have to adjust clothing. I don't care what I'm wearing, I can just go out in
whatever. I don't have to take anything with me.

One of the garage/yard salers wears shorts the entire year.

We routinely get heavy frosts at -10C and we are out at that time, in the dark.

No one else is that silly.

There are a few sensible people around. Wait till there's an ice age, then only people like him and me will survive.

I'll be basking in the sun in my passive solar house pointing
at your frozen corpse in the snow drift and laughing.

Your house has been carted off by a glacier.

And we wont bother to bury you either, bugger that. Let the wolves eat your corpse instead.

Reduce, reuse, recycle.

The house was designed passive solar so I bask in the sun on sunny
days in winter and everyone who visits comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

So you won't even have a room stat for heating?

I do, but dont use it anymore.

Don't you get some winters with a week of no sun?

Almost never, maybe once in 20 years.

Or does Australia have considerably less cloud than us?

Yep.

That's what I hate about the UK, cloud. Rain is fine, sun is fine, but cloudy all the time is boring.

Yeah, even a very heavy frost is quite pleasant when its
sunny, particularly when I'm basking in it in my passive
solar house looking out over the oval of the school thats
quite close with the entire area bright white from the frost.

And observing kids falling over and cracking their skulls open :-)

We dont get snow here.

Never missed skiing?

Engine cooling.

Why would engine cooling require anything more accurate then 4C hysteresis?

No idea. I just noticed that when I was trying to find an decent summary of why bi metallic thermostats normally have
a heater, on the web.

My Golf (1998 model) does seem to keep PRECISELY at 90C on the guage. Older vehicles never used to do that. Maybe it
makes the engine more efficient, or produce less pollution,

Yeah, likely, I meant to say that and forgot to say it.

How do you find the Golf ? My previous was a 72, lasted 35+ years
until I was stupid enought to not bother to fix the windscreen leak that
I kinew produced a wet floor when it rained much until that eventually
rusted a hole in the floor and was no longer registerable and not
economic to repair.

I have a hole in the floor too. I think it's from a leak in the sunroof.

It also has both locks busted, the radio-locking is broken, the passenger window doesn't work, the bonnet catch is busted, and the rear washer is broken. Like any other car there are little bits that go wrong that I don't bother fixing as they aren't really necessary. But it is very reliable as far as being able to start easily and never breaking down. It's never need anything doing to prevent it from being unusable.

It does save quite a bit on the cost of heating if you are out much.

If I go away for a day (as in come back the next day) or more, I'll either switch it off or change the stat to frost
protection. But just out for 8 hours, no.

You'd reduce your heating costs quite a bit if you did.

I don't believe it would be that much. After all when I come back it has to warm the house back up.

Thats another very common misapprehension. Its just
basic physics that you lose significantly less at the house
lower temps, because loss is entirely determined by the
temperature differential all other factors kept constant.

I know. But if it's 0C outside, and the house cools from 20C to 17C, then it still has a similar difference.

If it's 10C outside, then the house wouldn't have cooled by much in that time period.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

I don't prefer a different temperature during the day and at night. If I did it would be a nuisance, because I'd
have to cool the house instantly to the night time temperature before going to bed, then warm it up instantly in the
morning.

There is no need for any instantly, modern digital thermostats
anticipate the setpoint, now how long it takes to move between
the setpoints and just stop heating at the appropriate time at bed
time and start heating before the daytime setpoint in the morning
so when you get up, its at the temp you say you want.

That would be fine if you got up at an exact time every day.

Doesnt have to be exactly. If you set it for the earliest
time you normally get up, you still save significantly.

Although it would still be a problem - either the house is cooling down before your bedtime,

Nope, it just stops heating then.

or you are going to bed with the house too warm.

Not if you have enough of a clue to have a different zone temp
for the bedroom from wherever you are before you go to bed.

Taint rocket science.

I don't wish to isolate parts of my house. It's a small house, and I tend to leave internal doors open for convenience.

--
http://petersparrots.com
http://petersphotos.com

A waiter brings the customer the steak he ordered with his thumb over the meat.
"Are you crazy?" yelled the customer, "with your hand on my steak?"
"What" answers the waiter, "You want it to fall on the floor again?"

On Tue, 6 Mar 2012 07:56:10 -0800 (PST), RobertL
wrote:

On Mar 6, 3:29*am, "Rod Speed" wrote:
Brian Gaff wrote

A.Lee wrote
DerekG wrote
It's a bit like trying to throw a Yo-Yo away whilst still holding onto the string. And yes it's a crap plumbers
idea.
It isnt. I've been on a training course that shows the graphs of heat and gas used. The heated stats use less gas,
and keep the room at a steadier temperature than the standard on/off stats.
That though depends on the *site of the stat, and how well designed the placement of the radiators were in the first
place.

Nope, you always get a benefit.

The only real downside is that the system switches more.

and doesn't warm up from cold so fast.

Robert

I don't follow.
Stat calls for heat.
Heater/boiler runs full pelt until setpoint is reached.
Stat turns off heat.


--
Graham.
%Profound_observation%

On Mon, 5 Mar 2012 12:09:02 -0800 (PST), "js.b1"
wrote:

On Mar 5, 3:21*pm, Graham. wrote:
OK confession time.
For a long time I had the neutral terminal of my room stat connected
to the CPC because there was no neutral. The CU didn't contain an RCD
at the time

SI 2002 #2665, ESQCR.
"A consumer shall not combine the neutral and protective functions in
a single conductor in his consumer's installation."

Reason being whilst the earth tests as dead, when you disconnect the
CU earth then every single (electrically) earthed object in the house
including gas & water pipes re MEB is now a floating live whose
ability to shock is only limited by the resistor (in this case).


820k in this case, so less than 30mA if my maths are right.

Oh and just remembered I think the two indicator neons in the control
box were returned to earth for the same reason.


So the next time John Prescott comes around... :-)

'Twas a long time ago, I'll plead the statute of limitations.


--
Graham.
%Profound_observation%

Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote
Rod Speed wrote
Lieutenant Scott wrote Sure, but does appear to have a problem with presenting much more
of an inductive load than the bi metallic thermostats can handle.

The digistat is happy enough

Sure, but its likely to have been designed to handle motorised valves.

Shouldn't any stat handle one?

Not if it hasnt got magnetised contacts to provide a snap action.

Presumably then it shouldn't have a rating for inductive load? I'm sure it did.

Presumably another one from china. All bets are off with the 'ratiings' with those.

It's not like it's a BIG load, although it's inductive, but they should be able to handle that?

Not if it hasnt got magnetised contacts to provide a snap action.

You did say that at least one of yours doesnt.

I said maybe that's the problem with them. I haven't looked closely enough to see if they have magnets.

Where did you get its inductive load figure from ?

I didn't. I was guessing that's why it caused the arc.

Actually...... I now remember trying a couple of the stats at one
time to run a cooling fan. It's just as 30 watt extractor - much like you'd buy for a kitchen. The same problem
occurred with that. Maybe I did have a load of crap stats? They all definitely gave a rating for inductive, so I
assume they were designed to handle inductive.

Bet you'll find if you actually compare the inductive
load with the rating that both exceed it by quite a bit.

The inductive rating I remember as being a couple of amps. It was not a 480 watt fan. It was 30 watts.

You cant jjust use the amps with inductive loads.

Then why do they state them?

They are chinese.

That is NOT how the heater works. It just sees the thermostat
turn off sooner than it would do without a heater. There is no
attempt what so ever to produce a discrete temperature
difference. As you say, that isnt even possible.

Well if it's not that accurate, then it's just a guess it's doing.

Nope, its not even attempting to do anything about measuring
or estimating temperature, its JUST heating the strip so that
it opens quicker than it would otherwise do without a heater.

No guessing what so ever involved at all.

It's the equivalent of a guess

Nope, nothing like it. Something else entirely.

- yes I know it doesn't have the ability to "think", but it's not measuring the room temperature directly,

Yes it is when it turns ON when the heater is off.

it's measuring the combination of the room temperature and the output of the resistor.

Nope, not when the it turns on and the heater is off.

It doesnt do that when turning off either, when its turning
off, it isnt even using the air temp at all, the heater just
turns it off well before it would otherwise turn off to
significantly reduce the hysteresis.

THEN it measures the air temp again, with the resistor off.

Exactly.

Fraid not.

It's turning off when it shouldn't,

Nope, its turning off when it should to reduce the hysteresis.

therefore the heater is not on as long as it needs to be to keep the room warm.

Wrong, it just comes on again sooner and keeps the room more
evenly warm than otherwise, because of the reduced hysteresis.

STILL no guessing of the temperature.

Most find it more confortable. There arent too many that are
happy with a 4C hysteresis that you are happy to accept.

I don't even notice a 4C change.

I do.

You said you don't mind it being really warm though.

Thats a different effect to when its say 20C

So presumably varying from your minimum comfortable temperature to 4C higher wouldn't bother you?

It does bother me when its 4C colder than I prefer.

Why not set your room temperature so that you aren't near the minimum of your comfort zone?

There is no such thing. The temp I require varys with
what I am wearing and what I am doing etc etc etc.

As I said most people have a zone of comfort, not one precise temperature.

If that was true, they wouldnt have been able to sell any of the bi metallic
strip thermostats for a higher price than the ones without heaters.

There is no need for great accuracy in room temperatures.

Most clearly feel otherwise.

I've seen some people actually put on a jacket to go form a heated house to a heated car,

I would if I am wearing just a T shirt in the heated house.

Even if it's only for a minute?

Yep, because its a lot more than a minute in total
for the whole trip when going out shopping etc.

But most of the time you are in a heated car or a heated shop.

And I prefer not to feel too cold when moving
between the car in the carpark and the shop etc.

And I always take a top when flying, because they run the planes
too cold for my likely when wearing just a T shirt and shorts and
thongs/flip flops as I always do in spring/summer/autumn.

Corse when we are having one of those 10 days over
40C the plane can get ****ING hot on the ground when
they turn it off for refueling with the passenger still on
board at the intermediate stops with the Saab 340Bs.

Surely the specific heat capacity of your body causes you to take a while to cool down.

Your core temp doesnt change. You feel the cold when
your skin temp drops significantly unless you are like that
mate of mine that wears shorts right thru the entire winter.

Your skin temp is irrelevant.

Not to my comfort it aint.

Even if you are stupid enough to lie down naked in
a snow drift, your core body temp wont be affected
but even you might feel a tad uncomfortable.

Another one doesnt go quite that far, but doesnt wear
much on top. He's pretty fat tho and I keep reminding him
that its his fat that keeps him warm, its a built in jacket.

I find fat people usually feel the cold more,

None of the ones I know do and one of them is by far the fattest person
I have ever seen in person, even tho I have seen fatter ones in docos.

We all call him Huge for a reason.

as they are fat due to a low metabolism.

Nope because they shovel more calories into their mouths than they burn.

He eats VASTLY more than any of the rest of us do.

He's one of the motorhomers and while everyone else
talks about particular towns about particular things unique
to that town, with him, thats where there is a pastry shop
with a particularly good line in cream cakes etc.

When he shows up to visit anyone, he usually brings a great
swag of that sort of thing. The others eat one or two each
and he wolfes down the vast bulk of what he brought.

Never seen anything like it.

Unless of course they're just greedy buggers.

They all are.

One of the kids who isnt even out of primary school yet
weighs more than I do and routinely wolfes down a whole
pizza as a quick snack between meals if he can get it.

Even he does wear a top when we are standing
around in the dark with a heavy frost at -10C for
an hour so outside with a decent wind.

The one who wears shorts right thru the winter doesnt show up that early.

I used to ride to school on a bike when I was a kid and in the depths
of winter, my ears felt like they might freeze off after the long downhill run. I wasnt stupid enough to do that
wearing just a T shirt and shorts.

That'll be why you're not used to it then. Kids these days are wrapped in cotton wool,

Try telling that that to my GP. His kid was showing
off to his mates riding his bike along the top of a
waist high wall at the school, fell off and broke is arm.

so when they get to adulthood, they're wimps.

Must be why they get killed surfing on car roofs etc.

I actually take pff my fleece that I wear over a sweat over the T
shirt in winter when I go out in all but the most extreme weather.
I leave the fleece on in the most extreme weather and when doing
the garage/yard sale run in the depths of winter because the
regulars often stand around talking waiting for somewhere to open
and that can be damned cold, particularly with a heavy frost.

http://i0.kym-cdn.com/entries/icons/...4/facepalm.jpg

Stop crying boy, you some sort of bald sook ?

That was not a cry, that was a "facepalm".

SURE it was. Pity about the sobbing that blows that claim completely out of the water.

but surely most folk aren't that bad. Has most of society really
forgotten how to moderate their own body temperature?

Most choose to do what is most comfortable, including me.

The trouble is people are becoming worse.

The damned ancient greeks used to sit around in
their togas or whatever they wore and howl like that.

What?

You deaf ?

In a few more generations, we'll be wanting thermostats with a 0.1C accuracy, and we simply won't be able to go
outside at all.

We used to drive around in unheated cars in the
depth of winter and now arent that stupid anymore.

That change didnt actually produce the end
of civilisation as we know it for some reason.

It was unnecessary (apart from increasing driving visibility).

So are cars.

We are getting more and more expensive ways of being comfortable, and more and more things we won't have but are used
to when they fail.

You're always free to go back to a cave if you want.

Corse they fail too.

Locally, no one did anything much special during the inevitable
10 days over 40C that happens many years. Now almost
everyone has at least an evaporative cooler, what the yanks
call a swamp cooler, and many have full airconditioning.

I can remember one car trip in conditions like that in a car
with no airconditioning at all. It was so ****ing hot that we
pulled up at a river and just jumped in the water and stayed
there in the shade in the water until the sun started to go down.

In those temps, wearing more clothes can be useful,

Nope. I built the house from scratch myself wearing just shorts, not even a T shirt.

with regular soakings of water. Lots of evaporation.

Doesnt work too well inside a car.

Yes, whipping yourself furiously when naked can help
a bit in winter, but I prefer to wear more clothes myself.

When I go out for exercise, I try to anticipate what I will be
wearing at the end of the very long walk, because it irritates me
to have to have removed the sweat because the movement has warmed me up and the air has warmed up. I normally start
at first light, when its just light enough so I dont trip over stuff. I dont walk
around the streets, too boring, I normally walk in the bush/scrub
areas on the hills at the back of town for 1:30-2 hours.

I don't have to do that anticipation :-P

And arent as comfortable as me.

I don't notice the temperature.

You would with one of our 10 days over 40C

And you dont get that with a bi metallic strip thermostat with no heater.

You get a few degrees. Which is more than 1 :-P

Its more than most's preferred comfort range which is
why heaters in bi metallic thermostats were invented.

The wouldnt bother with an extra cost item like that if
most dont prefer the reduced hysteresis that produces.

I doubt a resistor costs that much.

Still cost more than not having it.

It's probably more that un-knowledgable people will think they're
faulty if they have a 4C hysteresis and be liable to send them back.

Nope. Most prefer a lower hysteresis when it can be achieved that cheaply.

But I disagree on WHY they want it.

Irrelevant, they want it anyway.

But I definitely an not anaemic.

I'll settle for wimp then.

That wont fly either with the hot weather.

We routinely have 10 days over 40C,

If you lot got that much you'd be dying like flys.

I went to the South of France when they had that heatwave that killed hundreds of people. It didn't bother me. I
became
accustomed to it within a couple of days.

You'd be dead if you tried digging ditches in ours.

I'd get used to it.

Not even possible. People die if they are that stupid.

As long as I was permitted to take my shirt off that is. And some drinks!

You'd still end up dead.

Sure, but there isnt any point in doing that, I prefer to be
comfortable instead.

And its no big deal to put a top on over the T shirt before
anyone else does.

It's a lot more convenient not to have to adjust clothing. I
don't care what I'm wearing, I can just go out in whatever. I don't have to take anything with me.

One of the garage/yard salers wears shorts the entire year.

We routinely get heavy frosts at -10C and we are out at that time, in the dark.

No one else is that silly.

There are a few sensible people around. Wait till there's an ice age, then only people like him and me will
survive.

I'll be basking in the sun in my passive solar house pointing
at your frozen corpse in the snow drift and laughing.

Your house has been carted off by a glacier.

Not even possible here, too flat.

And we wont bother to bury you either, bugger that. Let the wolves eat your corpse instead.

Reduce, reuse, recycle.

The house was designed passive solar so I bask in the sun on sunny days in winter and everyone who visits
comments on how warm it is.

I dont heat the house in winter, the most I do is use a heated
throw, sort of like an electric blanket, takes bugger all power.

We dont get that many heavy overcast days which dont get
above 0C and the heated throw works fine on those rare days.

So you won't even have a room stat for heating?

I do, but dont use it anymore.

Don't you get some winters with a week of no sun?

Almost never, maybe once in 20 years.

Or does Australia have considerably less cloud than us?

Yep.

That's what I hate about the UK, cloud. Rain is fine, sun is fine, but cloudy all the time is boring.

Yeah, even a very heavy frost is quite pleasant when its
sunny, particularly when I'm basking in it in my passive
solar house looking out over the oval of the school thats
quite close with the entire area bright white from the frost.

And observing kids falling over and cracking their skulls open :-)

Nar, their skulls are too thick for that |-)

We dont get snow here.

Never missed skiing?

We do have much more skiable areas than you do, just not where I personally live.

Engine cooling.

Why would engine cooling require anything more accurate then 4C hysteresis?

No idea. I just noticed that when I was trying to find an decent summary of why bi metallic thermostats normally
have a heater, on the web.

My Golf (1998 model) does seem to keep PRECISELY at 90C on the guage. Older vehicles never used to do that. Maybe
it makes the engine more efficient, or produce less pollution,

Yeah, likely, I meant to say that and forgot to say it.

How do you find the Golf ? My previous was a 72, lasted 35+ years
until I was stupid enought to not bother to fix the windscreen leak that I kinew produced a wet floor when it rained
much until that eventually rusted a hole in the floor and was no longer registerable and not
economic to repair.

I have a hole in the floor too. I think it's from a leak in the sunroof.

It also has both locks busted, the radio-locking is broken, the passenger window doesn't work, the bonnet catch is
busted, and the rear washer is broken.

Sounds like the yanks are right, they've gone down hill a lot since mine.

Like any other car there are little bits that go wrong that I don't bother fixing as they aren't really necessary.

That wasnt the case with mine over a much longer period than yours.

And it hasnt happened with the Hyundai Getz I replaced it with either.

Not one warranty quibble in the 5 year warranty. Even the Golf didnt manage that.

Or the beetle that I had before the Golf either.

I only replaced that with the Golf because I had a ****ing
great Alsatian that was absolutely obsessed with having
his head out the window, even in the depths of winter
and on long trips lasting days at highway speeds.

The beetle only has one opening window on each side and in
summer the bugger used to slobber down the back of my neck.

The Golf fixed that, he got his own window and its got a heater
that allows him to have his way even in the depths of winter.

But it is very reliable as far as being able to start easily and never breaking down. It's never need anything doing
to prevent it from being unusable.

Yeah thats true of the yank ones too, the stuff that
falls off is minor stuff that doesnt affect its driveability.

It does save quite a bit on the cost of heating if you are out much.

If I go away for a day (as in come back the next day) or more, I'll either switch it off or change the stat to
frost protection. But just out for 8 hours, no.

You'd reduce your heating costs quite a bit if you did.

I don't believe it would be that much. After all when I come back it has to warm the house back up.

Thats another very common misapprehension. Its just
basic physics that you lose significantly less at the house
lower temps, because loss is entirely determined by the
temperature differential all other factors kept constant.

I know. But if it's 0C outside, and the house cools from 20C to 17C, then it still has a similar difference.

You still save by turning it off when you arent there.

And only a super insulated house will only drop
3C with it 0C outside if you are out all day.

If you do have a super insulated house, you dont need a boiler.

If it's 10C outside, then the house wouldn't have cooled by much in that time period.

And it makes no sense to keep the house at the temp you
prefer during the day, all night when you are in bed etc.

I don't prefer a different temperature during the day and at
night. If I did it would be a nuisance, because I'd have to cool
the house instantly to the night time temperature before going to bed, then warm it up instantly in the morning.

There is no need for any instantly, modern digital thermostats
anticipate the setpoint, now how long it takes to move between
the setpoints and just stop heating at the appropriate time at bed
time and start heating before the daytime setpoint in the morning
so when you get up, its at the temp you say you want.

That would be fine if you got up at an exact time every day.

Doesnt have to be exactly. If you set it for the earliest
time you normally get up, you still save significantly.

Although it would still be a problem - either the house is cooling
down before your bedtime,

Nope, it just stops heating then.

or you are going to bed with the house too warm.

Not if you have enough of a clue to have a different zone temp
for the bedroom from wherever you are before you go to bed.

Taint rocket science.

I don't wish to isolate parts of my house. It's a small house, and I tend to leave internal doors open for
convenience.

Hardly the end of civilisation as we know it to open the bedroom door once a day.