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From: ransley on 30 Jan 2010 07:49
On Jan 29, 7:01 pm, DGF <non...(a)noplace.nospam> wrote:
> How do you verify that a battery-powered digital thermostat is working
> like it should? From what I've read, it seems that it is supposed to
> electrically bridge the connection between R wire and the W wire, when
> it turns on heating. I detached a thermostat from the HVAC system and
> tested the connection between the two terminals using a multimeter *when
> the room temperature was well below the heating set-point*; the contacts
> on the thermostat corresponding to the R & W wires didn't seem to allow
> current to flow through. Given that it's an electronic device and may
> not respond to the small DC voltage from the multimeter the same way it
> may to 24 VAC, I can't tell whether the thermostat is good or bad.
>
> Any ideas?

Hook it up like its intended to be, and with power off, jump it or
power it wrong and it will be trash.
From: Dave Plowman (News) on 30 Jan 2010 08:05
In article <hk00ce$f9b$1(a)speranza.aioe.org>,
DGF <noname(a)noplace.nospam> wrote:
> How do you verify that a battery-powered digital thermostat is working
> like it should? From what I've read, it seems that it is supposed to
> electrically bridge the connection between R wire and the W wire, when
> it turns on heating. I detached a thermostat from the HVAC system and
> tested the connection between the two terminals using a multimeter *when
> the room temperature was well below the heating set-point*; the contacts
> on the thermostat corresponding to the R & W wires didn't seem to allow
> current to flow through. Given that it's an electronic device and may
> not respond to the small DC voltage from the multimeter the same way it
> may to 24 VAC, I can't tell whether the thermostat is good or bad.

Can you hear it operate? Mine has a sort of electrically operated switch
rather than solid state or relay type to reduce battery consumption and
are clearly audible when they make or break. It also only operates when in
its housing so to test you'd need to bring out wires from that to connect
to a DVM.

--
*I feel like I'm diagonally parked in a parallel universe*

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
From: Dave Plowman (News) on 30 Jan 2010 08:11
In article
<ecf06c6d-6550-4716-9829-9249e92ed919(a)21g2000yqj.googlegroups.com>,
Mikepier <mikepier(a)optonline.net> wrote:
> I think he's right. Most T-stats have "power stealing" circuitry,
> meaning they depend on the 24VAC from the HVAC system.

In the UK the switching volts can be mains. So these universal
programmable stats seem to have some form of electrically operated switch
which is isolated from the actual device - rather in the same way as a
relay. But because they only take current from the battery when they alter
status are more suited to this sort of app.

--
*Virtual reality is its own reward *

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
From: Gnack Nol on 30 Jan 2010 18:08
On Sat, 30 Jan 2010 03:06:51 -0800, Mikepier wrote:

> On Jan 29, 9:16�pm, PeterD <pet...(a)hipson.net> wrote:
>> On Fri, 29 Jan 2010 20:01:01 -0500, DGF <non...(a)noplace.nospam> wrote:
>> >How do you verify that a battery-powered digital thermostat is working
>> >like it should? From what I've read, it seems that it is supposed to
>> >electrically bridge the connection between R wire and the W wire, when
>> >it turns on heating. I detached a thermostat from the HVAC system and
>> >tested the connection between the two terminals using a multimeter
>> >*when the room temperature was well below the heating set-point*; the
>> >contacts on the thermostat corresponding to the R & W wires didn't seem
>> >to allow current to flow through. Given that it's an electronic device
>> >and may not respond to the small DC voltage from the multimeter the
>> >same way it may to 24 VAC, I can't tell whether the thermostat is good
>> >or bad.
>>
>> >Any ideas?
>>
>> Like making a test circuit that provides the necessary 24 volts?
>
> I think he's right. Most T-stats have "power stealing" circuitry, meaning
> they depend on the 24VAC from the HVAC system.



That is correct thermostats electronic or mechanical always depend on the
power source in the HVAC system they control for power and are never self
powered.

The battery is just there for power interruptions to keep the thermostat
from resetting to a different temperature nothing more.

To test it you will have to provide the 24v source for it to operate from
otherwise nothing will happen.

Gnack
From: Dave Plowman (News) on 31 Jan 2010 05:37
In article <pan.2010.01.30.23.08.19.952330(a)mailinator.com>,
Gnack Nol <mchozfcesujcfc(a)mailinator.com> wrote:
> That is correct thermostats electronic or mechanical always depend on the
> power source in the HVAC system they control for power and are never self
> powered.

In the UK that's simply not true. There are many different makes that
operate entirely on battery power. And can be used to control a mains *or*
low voltage circuit. I'd be very surprised if the same models weren't on
sale in the US. Something like these:-

http://www.tlc-direct.co.uk/Main_Index/Heating_Index/Therm_3/index.html

which are a very good way of upgrading an older system. Better modern
ones tend not to have a room stat but a simple temperature sensor with the
house temp being set via the boiler electronics.

I know US systems can be different from UK ones - but the same principles
must apply. And much needed in these days of high energy prices.

--
*I have a degree in liberal arts -- do you want fries with that

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
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