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.