I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

On Saturday 23 February 2013 08:19 wrote in alt.home.repair:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

Some do, out of design laziness. They find it easier to require batteries
and drive a relay ensuring complete isolation between mains and control
interface.


--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

On 2/23/2013 2:19 AM, wrote:
I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J


Most digital thermostats will run on batteries or 24 volts AC with the
batteries being used to maintain memory for the settings. Your old round
Honeywell thermostat had a coiled bi-metallic spring attached to a
mercury switch to control your HVAC system. It was mechanical requiring
no extra power to function since it was a simple switch. The cable for
the older mechanical heat/cool/fan thermostats had only 4 or 5 wires
and when your new digital thermostat was installed there may have been
only enough wires to provide basic control signals to the furnace and
no spare wire to provide a common ground for 24 volt power from the
air handler/furnace. ^_^

TDD

You should call the installer, and ask him. We'd only be guessing. Many
thermostats are line powered, but yours appears to be the exception. Who
knows, maybe it was wired wrong.

Christopher A. Young
Learn more about Jesus
www.lds.org
..

wrote in message
...
I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

On Feb 23, 4:48*am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 2/23/2013 2:19 AM, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. *I noticed the other night that it was cold in the
house. *I checked the thermostat and it said "replace the batteries",
which I did and all was well again. *I thought the Honeywell
thermostat ran on ac from the furnace. *Apparently mine doesn't but
runs on the batteries only. *Is this the way it is supposed to be or
did the techs who installed the system not wire it right? *I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

Most digital thermostats will run on batteries or 24 volts AC with the
batteries being used to maintain memory for the settings. Your old round
Honeywell thermostat had a coiled bi-metallic spring attached to a
mercury switch to control your HVAC system. It was mechanical requiring
no extra power to function since it was a simple switch. The cable for
the older mechanical heat/cool/fan thermostats had only 4 or 5 wires
and when your new digital thermostat was installed there may have been
only enough wires to provide basic control signals to the furnace and
no spare wire to provide a common ground for 24 volt power from the
air handler/furnace. ^_^

TDD

+1

Not sure about most running on 24V or batteries though.
There are certainly both kinds though, but agree with the
analysis. If it was a system with an old mechanical
thermostat, it's very possible that there was not an extra
wire available to supply the 24V. In which case, using a
battery only thermostat is probably what almost
every installer would do.

There should be an installation manual for the thermostat, available
online if he doesn't have one, which answers the question of
if the thermostat supports being powered by 24V. If it does,
then the question is if there is an extra wire available, if he
wants to run new cable, if it's worth it, etc. There are a
lot of thermostats out there that are battery only. Another
thing that may be of interest is if the thermostat has a
failsafe mode where a mechanical switch closes at around
45 or so to prevent freezing in case the batteries go
dead.

On Sat, 23 Feb 2013 02:19:04 -0600, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J


Welcome to the age of electronics.

That old round stat had a glass bulb filled with mercury. When it
expanded and contracted with changes in temperature, it would make or
break the contacts. Simple, reliable, repeatable, albeit in a fairly
big off and on range for the setting.

with electronics, you can program different temperatures for different
days and different times of day and for heating and cooling. They also
hold it steady at a fairly narrow range.

Regardless of what actually power the workings, you need power
constantly to maintain the memory. Enter a battery. Most will last
at least a year, some much more. Make it a habit to replace the
battery once a year at the same time you do the smoke detectors.

On 2/23/2013 7:06 AM, wrote:
On Feb 23, 4:48 am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 2/23/2013 2:19 AM, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

Most digital thermostats will run on batteries or 24 volts AC with the
batteries being used to maintain memory for the settings. Your old round
Honeywell thermostat had a coiled bi-metallic spring attached to a
mercury switch to control your HVAC system. It was mechanical requiring
no extra power to function since it was a simple switch. The cable for
the older mechanical heat/cool/fan thermostats had only 4 or 5 wires
and when your new digital thermostat was installed there may have been
only enough wires to provide basic control signals to the furnace and
no spare wire to provide a common ground for 24 volt power from the
air handler/furnace. ^_^

TDD

+1

Not sure about most running on 24V or batteries though.
There are certainly both kinds though, but agree with the
analysis. If it was a system with an old mechanical
thermostat, it's very possible that there was not an extra
wire available to supply the 24V. In which case, using a
battery only thermostat is probably what almost
every installer would do.

There should be an installation manual for the thermostat, available
online if he doesn't have one, which answers the question of
if the thermostat supports being powered by 24V. If it does,
then the question is if there is an extra wire available, if he
wants to run new cable, if it's worth it, etc. There are a
lot of thermostats out there that are battery only. Another
thing that may be of interest is if the thermostat has a
failsafe mode where a mechanical switch closes at around
45 or so to prevent freezing in case the batteries go
dead.


Of the digital thermostats I install I always pickup the dual powered
units at the supply house. They're not that expensive and I will usually
go with the non-programmable unless a customer requests one. ^_^

http://www.pexsupply.com/Venstar-T01...tal-Thermostat

http://tinyurl.com/ao5dtph

TDD

On 2/23/2013 7:06 AM, wrote:
On Feb 23, 4:48 am, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 2/23/2013 2:19 AM, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

Most digital thermostats will run on batteries or 24 volts AC with the
batteries being used to maintain memory for the settings. Your old round
Honeywell thermostat had a coiled bi-metallic spring attached to a
mercury switch to control your HVAC system. It was mechanical requiring
no extra power to function since it was a simple switch. The cable for
the older mechanical heat/cool/fan thermostats had only 4 or 5 wires
and when your new digital thermostat was installed there may have been
only enough wires to provide basic control signals to the furnace and
no spare wire to provide a common ground for 24 volt power from the
air handler/furnace. ^_^

TDD

+1

Not sure about most running on 24V or batteries though.
There are certainly both kinds though, but agree with the
analysis. If it was a system with an old mechanical
thermostat, it's very possible that there was not an extra
wire available to supply the 24V. In which case, using a
battery only thermostat is probably what almost
every installer would do.

There should be an installation manual for the thermostat, available
online if he doesn't have one, which answers the question of
if the thermostat supports being powered by 24V. If it does,
then the question is if there is an extra wire available, if he
wants to run new cable, if it's worth it, etc. There are a
lot of thermostats out there that are battery only. Another
thing that may be of interest is if the thermostat has a
failsafe mode where a mechanical switch closes at around
45 or so to prevent freezing in case the batteries go
dead.


If your thermostat cable contains 5 wires and you have a single stage
heat and cool thermostat there are enough wires to get 24 volt power
to the thermostat unless the installer is lazy. ^_^

C -- Red 24 volt hot
W -- White Heat
Y -- Yellow Cool
G -- Green Fan

B -- Blue 24 volt common/ground often connected to the air handler
cabinet.

TDD

On Saturday 23 February 2013 13:19 Ed Pawlowski wrote in alt.home.repair:


Regardless of what actually power the workings, you need power
constantly to maintain the memory. Enter a battery. Most will last
at least a year, some much more. Make it a habit to replace the
battery once a year at the same time you do the smoke detectors.

There are a couple of other options:

E2PROM which is common on many microcontrollers (eg Atmel AVRs, my personal
favourite 8 bit) and you don't need much even on a 7 day stat with 4
periods/day.

Supercapacitors which at low voltages are very small for something with a
farad odd of capacity which would keep a bit of SRAM going for a long time
in power outages.

Though you really need the supercap either way to keep the clock running -
but programming in E2 is cute in that it relly will *not* go away by
accident and makes doing a device reset much easier.



I think the real reason is that testing/approval for anything with a mains
(120 or 240V) PSU is considered "hard" (and is probably harder than it was
say 30 years ago). That's why so many things these days have wallwarts -
leave the PSU isolated and the design to mains specialists.

A modular PSU is not so much of an option for a tiny form factor device.

Ironically, you could virtually run these things with a reactive dropper and
a rectifier as the demands are so low - but then your circuits are no longer
isolated from the mains, which is not necessarily a problem (eg the pot on a
dimmer switch is wired into the mains) but it gives designers heebie jeebies
and does demand more testing.

BTW - did the US really have mercury stats? I've never seen a non electronic
one that wasn't a bi-metallic mechanism in all of 40 years in the UK and
that includes a fair few Honeywells.

--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

On Sat, 23 Feb 2013 02:19:04 -0600, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J
The old round honeywell didn't "run" on anything - it was a simple
mercury switch on a bimetal spring. My electronic stat runs on the 24
volt thermostat supply transformer but has a battery to back-up the
memory settings in case of power failure. It will still operate with
a dead battery but I believe if the power were to go out the clock
would lose it's setting and the thermostat would revert to a preset
fall-back setting.

On Sat, 23 Feb 2013 14:58:07 +0000, Tim Watts
wrote:

On Saturday 23 February 2013 13:19 Ed Pawlowski wrote in alt.home.repair:


Regardless of what actually power the workings, you need power
constantly to maintain the memory. Enter a battery. Most will last
at least a year, some much more. Make it a habit to replace the
battery once a year at the same time you do the smoke detectors.

There are a couple of other options:

E2PROM which is common on many microcontrollers (eg Atmel AVRs, my personal
favourite 8 bit) and you don't need much even on a 7 day stat with 4
periods/day.

Supercapacitors which at low voltages are very small for something with a
farad odd of capacity which would keep a bit of SRAM going for a long time
in power outages.

Though you really need the supercap either way to keep the clock running -
but programming in E2 is cute in that it relly will *not* go away by
accident and makes doing a device reset much easier.



I think the real reason is that testing/approval for anything with a mains
(120 or 240V) PSU is considered "hard" (and is probably harder than it was
say 30 years ago). That's why so many things these days have wallwarts -
leave the PSU isolated and the design to mains specialists.

A modular PSU is not so much of an option for a tiny form factor device.

Ironically, you could virtually run these things with a reactive dropper and
a rectifier as the demands are so low - but then your circuits are no longer
isolated from the mains, which is not necessarily a problem (eg the pot on a
dimmer switch is wired into the mains) but it gives designers heebie jeebies
and does demand more testing.

BTW - did the US really have mercury stats? I've never seen a non electronic
one that wasn't a bi-metallic mechanism in all of 40 years in the UK and
that includes a fair few Honeywells.
What contacts are used on your "non mercury" bimetallic
Honeywells??? Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.

On Feb 23, 10:41*am, wrote:
On Sat, 23 Feb 2013 14:58:07 +0000, Tim Watts
wrote:





On Saturday 23 February 2013 13:19 Ed Pawlowski wrote in alt.home.repair:

Regardless of what actually power the workings, you need power
constantly to maintain the memory. *Enter a battery. * Most will last
at least a year, some much more. *Make it a habit to replace the
battery once a year at the same time you do the smoke detectors.

There are a couple of other options:

E2PROM which is common on many microcontrollers (eg Atmel AVRs, my personal
favourite 8 bit) and you don't need much even on a 7 day stat with 4
periods/day.

Supercapacitors which at low voltages are very small for something with a
farad odd of capacity which would keep a bit of SRAM going for a long time
in power outages.

Though you really need the supercap either way to keep the clock running -
but programming in E2 is cute in that it relly will *not* go away by
accident and makes doing a device reset much easier.

I think the real reason is that testing/approval for anything with a mains
(120 or 240V) PSU is considered "hard" (and is probably harder than it was
say 30 years ago). That's why so many things these days have wallwarts -
leave the PSU isolated and the design to mains specialists.

A modular PSU is not so much of an option for a tiny form factor device.

Ironically, you could virtually run these things with a reactive dropper and
a rectifier as the demands are so low - but then your circuits are no longer
isolated from the mains, which is not necessarily a problem (eg the pot on a
dimmer switch is wired into the mains) but it gives designers heebie jeebies
and does demand more testing.

BTW - did the US really have mercury stats? I've never seen a non electronic
one that wasn't a bi-metallic mechanism in all of 40 years in the UK and
that includes a fair few Honeywells.

* What contacts are used on your "non mercury" bimetallic
Honeywells??? *Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.- Hide quoted text -

- Show quoted text -

Yes, those were very common back in the 60s, 70s. Don't
know when they stopped making them. I also remember
back in the 60s they had AC wall switches that were the
silent type that used mercury.

The big issue with thermostats is not so much the memory
loss if the batteries die. It's that in areas subject to freezing
you could freeze the house due to a bad battery, if it's
unoccupied for a period. Some thermostats do have
some kind of failsafe 45F or so mechanical that kicks in,
but not all of them.

wrote in message
...
On Sat, 23 Feb 2013 02:19:04 -0600, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J
The old round honeywell didn't "run" on anything - it was a simple
mercury switch on a bimetal spring. My electronic stat runs on the 24
volt thermostat supply transformer but has a battery to back-up the
memory settings in case of power failure. It will still operate with
a dead battery but I believe if the power were to go out the clock
would lose it's setting and the thermostat would revert to a preset
fall-back setting.

If you go to a "Nest" thermostat, a new round one but electronic, it has a
self charging battery using power from the 24 volt transformer on the
furnace.
While no larger than the old Honeywell round, it is chock full of goodies
such as Wi-Fi and proximity sensors to detect when the house is occupied.

I have to disagree with the comments that have been made so far that your old thermostat "didn't run on anything" and was STRICTLY mechancial. That's simply not correct. Your old round Honeywell was PRIMARILY mechanical, but also used the 24 VAC power that it switched on and off in a tiny electric heater called a "heat anticipator heater" which was positioned next to the bi-metallic spring.

Basically, the old Honeywell consisted of a bimetallic spring that held a mercury switch on the end. That bimetallic spring would wind up and unwind depending on the indoor temperature, thereby making and breaking the circuit between the 120/24 VAC transformer in the boiler/furnace and the boiler furnace control to turn the boiler/furnace on or off.

But, wait, there's more...

In that old round Honeywell, there was an small electric heater that operated off of 24 VAC power that the thermostat switched on or off called a "heat anticipator heater".

Since every heating system is different, every thermostat in every house requires a different heat anticipator setting. Basically, it's the heat anticipator's job to heat the bi-metallic spring, thereby fooling the thermostat into thinking the room is warmer than it really is, and that results in the thermostat shutting the furnace or boiler off a little bit earlier, or a lot earlier, than it otherwise would, and I'll explain why.

Essentially, the heat anticipator is little more than a rheostat resistor whereby you can vary the length of wire the 24VAC power goes through, thereby changing the resistance of the resistor and thereby changing the amount of heat it generates. That resistor is physically located close to the bi-metallic spring so that the heat it generates warms the bimetallic spring causing the heating system to shut off earlier than it otherwise would.

That's because if that thermostat is being used on electric heat, then once the thermostat feels that the correct temperature in the room has been reached, then since the thermostat is centrally located in the room and the electric baseboard heaters are all located around the perimeter of the house, the AVERAGE temperature in the house has actually overshot the temperature setting on the thermostat. So, it woulda been better to shut the heating system off a bit earlier so that the AVERAGE temperature in the house is at the thermostat setting, not above it.

Similarily, if the thermostat is being used on a hot water heating system, then once those radiators get filled with 180 degree water, they're going to be convecting heat into the room for a long time after the boiler shuts off, so in that case you want a much higher heat anticipator setting on the thermostat.

And finally, in the case of a forced air heating system, when the thermostat detects the correct temperature in the room, the heat exchanger in the furnace is still hot, and it would make sense to keep the fan blowing until you get the heat from that heat exchanger into the occupied space, so again you want to shut the furnace off a bit early. The furnace has it's own switch that will keep the fan running until the heat exchanger in the furnace cools down.

Now, mechanical thermostats use a 24VAC heater to accomplish heat anticipation for different kinds of heating systems, but electronic ones do all of that electronically. It could be that the heat anticipator setting in your thermostat is way high to simulate the situation where the thermostat heats up well before the room is warm. In that case, your thermostat is shutting the heating system off way too early, and you just need to change that heat anticipator setting parameter.

So, try replacing your batteries.


If that doesn't solve the problem with your thermostat, then download the original documentation that came with that thermostat off the manufacturer's web site and see what it says about "Heat Anticipation" in the thermostat's set-up instructions. Or, do what most people do, which is to just tinker with the heat anticipator setting until the thermostat works well.

Thanks for the help guys. I called the installer and when I can get
an answer back I will know what to do. It looks easy enough to
run an extra wire or two for getting the 24v ac to the unit if that
was the problem. Probably the installer was lazy and didn't want
to do it right. Either way I think I want ac to the thermostat in
case I'm away from the house and the batteries die and the
house freeze up.



On Sat, 23 Feb 2013 07:16:48 -0500, "Stormin Mormon"
wrote:

You should call the installer, and ask him. We'd only be guessing. Many
thermostats are line powered, but yours appears to be the exception. Who
knows, maybe it was wired wrong.

Christopher A. Young
Learn more about Jesus
www.lds.org
.

On Saturday 23 February 2013 15:41 wrote in
alt.home.repair:

What contacts are used on your "non mercury" bimetallic
Honeywells??? Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.

Dry contacts - some sort of alloy that was common in switches - possibly
silver/cadmium - there were a few variants...

The bimetal mechanism had a "snap" action engineered into it to cause a
clean make and break. These stats tended to have quite a large hysteresis -
probably due in part to the snap action. So it was quite common to have a
small heater (nothing more than a 5W ish resistor under the bimetal strip to
cancel some of the hysteresis. It was wired between the stat output and
neutral to cause a bit of local heating when the stat was on "call for
heat". This was optional and required a neutral present at the stat, which
some installations did not have.

Looking at Wonkypedia, I do see a lot of historic info on thermostats with
mercury switches. Curious - never seen one here - and we never used to be
shy of mercury until the last decade or so...


--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

On Sat, 23 Feb 2013 14:22:29 -0500, "EXT"
wrote:


wrote in message
.. .
On Sat, 23 Feb 2013 02:19:04 -0600, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J
The old round honeywell didn't "run" on anything - it was a simple
mercury switch on a bimetal spring. My electronic stat runs on the 24
volt thermostat supply transformer but has a battery to back-up the
memory settings in case of power failure. It will still operate with
a dead battery but I believe if the power were to go out the clock
would lose it's setting and the thermostat would revert to a preset
fall-back setting.

If you go to a "Nest" thermostat, a new round one but electronic, it has a
self charging battery using power from the 24 volt transformer on the
furnace.
While no larger than the old Honeywell round, it is chock full of goodies
such as Wi-Fi and proximity sensors to detect when the house is occupied.

I have one in the house we're selling. It's a great thermostat but on
the pricey side. I'll probably buy another when we sell the place (in
a couple of weeks, hopefully) and change both in this house.

wrote:
I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

Hi,
You're talking about nalog vs. digital 'stat. You can make the new one
run on 24V AC using a power adapter. Ours is a wireless one so no wires
between 'stat and system. I use Lithium batteries which last ~3 years.

If your 'stat is not on battery, when there is a prolonged power outage,
programmed settings could be lost.

wrote:
On Feb 23, 10:41 am, wrote:
On Sat, 23 Feb 2013 14:58:07 +0000, Tim Watts
wrote:





On Saturday 23 February 2013 13:19 Ed Pawlowski wrote in alt.home.repair:

Regardless of what actually power the workings, you need power
constantly to maintain the memory. Enter a battery. Most will last
at least a year, some much more. Make it a habit to replace the
battery once a year at the same time you do the smoke detectors.

There are a couple of other options:

E2PROM which is common on many microcontrollers (eg Atmel AVRs, my personal
favourite 8 bit) and you don't need much even on a 7 day stat with 4
periods/day.

Supercapacitors which at low voltages are very small for something with a
farad odd of capacity which would keep a bit of SRAM going for a long time
in power outages.

Though you really need the supercap either way to keep the clock running -
but programming in E2 is cute in that it relly will *not* go away by
accident and makes doing a device reset much easier.

I think the real reason is that testing/approval for anything with a mains
(120 or 240V) PSU is considered "hard" (and is probably harder than it was
say 30 years ago). That's why so many things these days have wallwarts -
leave the PSU isolated and the design to mains specialists.

A modular PSU is not so much of an option for a tiny form factor device.

Ironically, you could virtually run these things with a reactive dropper and
a rectifier as the demands are so low - but then your circuits are no longer
isolated from the mains, which is not necessarily a problem (eg the pot on a
dimmer switch is wired into the mains) but it gives designers heebie jeebies
and does demand more testing.

BTW - did the US really have mercury stats? I've never seen a non electronic
one that wasn't a bi-metallic mechanism in all of 40 years in the UK and
that includes a fair few Honeywells.

What contacts are used on your "non mercury" bimetallic
Honeywells??? Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.- Hide quoted text -

- Show quoted text -

Yes, those were very common back in the 60s, 70s. Don't
know when they stopped making them. I also remember
back in the 60s they had AC wall switches that were the
silent type that used mercury.

The big issue with thermostats is not so much the memory
loss if the batteries die. It's that in areas subject to freezing
you could freeze the house due to a bad battery, if it's
unoccupied for a period. Some thermostats do have
some kind of failsafe 45F or so mechanical that kicks in,
but not all of them.

Hi,
Yes, our wireless one has RAS(return air sensor) mounted on the return
air duct. If whatever reason 'stat fails to communicate to the system
and the temp drops near freezing automatically temp setting falls back
like that to prevent freeezing.

Tim Watts wrote:
On Saturday 23 February 2013 15:41 wrote in
alt.home.repair:

What contacts are used on your "non mercury" bimetallic
Honeywells??? Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.

Dry contacts - some sort of alloy that was common in switches - possibly
silver/cadmium - there were a few variants...

The bimetal mechanism had a "snap" action engineered into it to cause a
clean make and break. These stats tended to have quite a large hysteresis -
probably due in part to the snap action. So it was quite common to have a
small heater (nothing more than a 5W ish resistor under the bimetal strip to
cancel some of the hysteresis. It was wired between the stat output and
neutral to cause a bit of local heating when the stat was on "call for
heat". This was optional and required a neutral present at the stat, which
some installations did not have.

Looking at Wonkypedia, I do see a lot of historic info on thermostats with
mercury switches. Curious - never seen one here - and we never used to be
shy of mercury until the last decade or so...

Hi,
You must be real OT like me. This is digital era. SS relays, AI logic
ASIC what you are talking about is past history. Fuzzy logic, AI are
taking over things like that.

It's possible it just needs one more wire, a common for the 24VAC, that's my
guess.

Christopher A. Young
Learn more about Jesus
www.lds.org
..

wrote in message
...

Thanks for the help guys. I called the installer and when I can get
an answer back I will know what to do. It looks easy enough to
run an extra wire or two for getting the 24v ac to the unit if that
was the problem. Probably the installer was lazy and didn't want
to do it right. Either way I think I want ac to the thermostat in
case I'm away from the house and the batteries die and the
house freeze up.



On Sat, 23 Feb 2013 07:16:48 -0500, "Stormin Mormon"
wrote:

You should call the installer, and ask him. We'd only be guessing. Many
thermostats are line powered, but yours appears to be the exception. Who
knows, maybe it was wired wrong.

Christopher A. Young
Learn more about Jesus
www.lds.org
.

On Sat, 23 Feb 2013 22:01:09 +0000, Tim Watts
wrote:

On Saturday 23 February 2013 15:41 wrote in
alt.home.repair:

What contacts are used on your "non mercury" bimetallic
Honeywells??? Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.

Dry contacts - some sort of alloy that was common in switches - possibly
silver/cadmium - there were a few variants...

The bimetal mechanism had a "snap" action engineered into it to cause a
clean make and break. These stats tended to have quite a large hysteresis -
probably due in part to the snap action. So it was quite common to have a
small heater (nothing more than a 5W ish resistor under the bimetal strip to
cancel some of the hysteresis. It was wired between the stat output and
neutral to cause a bit of local heating when the stat was on "call for
heat". This was optional and required a neutral present at the stat, which
some installations did not have.

Sounds like it was a Lucas thermostat - - - -.

Looking at Wonkypedia, I do see a lot of historic info on thermostats with
mercury switches. Curious - never seen one here - and we never used to be
shy of mercury until the last decade or so...

On Sat, 23 Feb 2013 20:57:45 -0500, "Stormin Mormon"
wrote:

It's possible it just needs one more wire, a common for the 24VAC, that's my
guess.

It's probably easier to use the existing wire to pull another with
enough wires to get the job done (plus a few). It didn't sound like
this was going to be a problem for the OP anyway.

On Sat, 23 Feb 2013 02:19:04 -0600, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

You have lots of answere, so here's an aside.

When I tried to buy a new furnace a couple years ago, one of the
sticking points was one salesmen who insisted I get a new thermostat.
I already have a heat/ac theromostat with 2 setbacks a day. I don't
want to buy another.

They don't sell this one anymore. Now they are all electronic, but
most of this uses mecfhanical switches. The temperature setting is by
2 mechancial slide switches with about 40 positions each, from 45 to
85. It also has 7 dip switches to choose one setback or two for each
of the 7 days of the week. But the clock is electronic. It has
batteries but it only needs them when the 24 volts isn't present, to
keep good time, and if one doesn't use the setbacks, it doesn't need
the time or the batteries to keep the temp right. Honeywell iirc. 30
years old, works fine. (I also have the round Honeywell which I
plan to put back before I move, someday, and I may use it as a temp
sensor for my home burglar alarm, to alert if the furnace breaks)

wrote:
On Sat, 23 Feb 2013 22:01:09 +0000, Tim Watts
wrote:

On Saturday 23 February 2013 15:41 wrote in
alt.home.repair:

What contacts are used on your "non mercury" bimetallic
Honeywells??? Every one I've ever seen had a "wet contact" bulb -
which had mercury in it. The bulb was about an inch long and 1/4 to
5/16 diameter with 2 wires coming out - 3 on the odd one.

Dry contacts - some sort of alloy that was common in switches - possibly
silver/cadmium - there were a few variants...

The bimetal mechanism had a "snap" action engineered into it to cause a
clean make and break. These stats tended to have quite a large hysteresis -
probably due in part to the snap action. So it was quite common to have a
small heater (nothing more than a 5W ish resistor under the bimetal strip to
cancel some of the hysteresis. It was wired between the stat output and
neutral to cause a bit of local heating when the stat was on "call for
heat". This was optional and required a neutral present at the stat, which
some installations did not have.

Sounds like it was a Lucas thermostat - - - -.

Looking at Wonkypedia, I do see a lot of historic info on thermostats with
mercury switches. Curious - never seen one here - and we never used to be
shy of mercury until the last decade or so...

LOL!
Lucas, knight of darkness.
Way back when my better hapf insisted on driving Sunbeam, I spent so
much time with it, every week end. Always something was going wrong.
Specially Lucas electrical system and that damn side draft twin Zenith
carb.,,,,.

micky wrote:
On Sat, 23 Feb 2013 02:19:04 -0600, wrote:

I had my old heat/ac system replaced a year or so ago with a new Rheem
heat/ac system. I noticed the other night that it was cold in the
house. I checked the thermostat and it said "replace the batteries",
which I did and all was well again. I thought the Honeywell
thermostat ran on ac from the furnace. Apparently mine doesn't but
runs on the batteries only. Is this the way it is supposed to be or
did the techs who installed the system not wire it right? I could
run wire with more connections if there wasn't enough wires.
The old round Honeywell apparently ran on ac because for 30 years it
didn't have batteries.

J

You have lots of answere, so here's an aside.

When I tried to buy a new furnace a couple years ago, one of the
sticking points was one salesmen who insisted I get a new thermostat.
I already have a heat/ac theromostat with 2 setbacks a day. I don't
want to buy another.

They don't sell this one anymore. Now they are all electronic, but
most of this uses mecfhanical switches. The temperature setting is by
2 mechancial slide switches with about 40 positions each, from 45 to
85. It also has 7 dip switches to choose one setback or two for each
of the 7 days of the week. But the clock is electronic. It has
batteries but it only needs them when the 24 volts isn't present, to
keep good time, and if one doesn't use the setbacks, it doesn't need
the time or the batteries to keep the temp right. Honeywell iirc. 30
years old, works fine. (I also have the round Honeywell which I
plan to put back before I move, someday, and I may use it as a temp
sensor for my home burglar alarm, to alert if the furnace breaks)
Hi,
You know new generation 'stats are much more accurate and it even has
some smart brain, not like old dumb mechanical ones.

older round thermostats used no power.....

You could put a old thermostat set as low as it could go say 45
degrees in parell with a new setback thermostat.

If the new thermost failed for dead battery or other reason the old
thermostat would prevent freezing..

On Sunday 24 February 2013 23:55 Tony Hwang wrote in alt.home.repair:


LOL!
Lucas, knight of darkness.
Way back when my better hapf insisted on driving Sunbeam, I spent so
much time with it, every week end. Always something was going wrong.
Specially Lucas electrical system and that damn side draft twin Zenith
carb.,,,,.

Lucas: Prince of Darkness, down my way...

Almost the crappiest cars ever built[1] (more or less everything by British
Leyland in the 70's) used Lucas parts somewhere - with the enevitable...

[1] Except Fiat, Lada and Trabant...

--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

On Mon, 25 Feb 2013 09:25:39 +0000, Tim Watts
wrote:

On Sunday 24 February 2013 23:55 Tony Hwang wrote in alt.home.repair:


LOL!
Lucas, knight of darkness.
Way back when my better hapf insisted on driving Sunbeam, I spent so
much time with it, every week end. Always something was going wrong.
Specially Lucas electrical system and that damn side draft twin Zenith
carb.,,,,.

Lucas: Prince of Darkness, down my way...

Almost the crappiest cars ever built[1] (more or less everything by British
Leyland in the 70's) used Lucas parts somewhere - with the enevitable...

[1] Except Fiat, Lada and Trabant...
Only one electrical system worse than Lucas was Paris Rhone