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From: Dave Plowman (News) on 1 Feb 2010 10:08
In article <hk6ovs$rb0$1(a)usenet01.srv.cis.pitt.edu>,
GregS <zekfrivo(a)zekfrivolous.com> wrote:
> >Battery operated thermostats don't have a conventional relay - ie one
> >which takes power all the time it's made. That would run down the
> >battery in short order. They use some form of 'motorised' switch, which
> >only takes power when it changes state. On mine you can hear it operate.
> >

> I always assumed a relay, and yes they are loud. On a soild state unit I
> could also hear a click, but I think that was from current flow. If
> units use a switch, I hope they have a safety overheat breaker.

Certainly in the UK it's a form of mechanical switch. It can carry mains
or low voltage AC or DC - not really possible with a solid state device.
My guess is it may be piezo operated. But that's only a guess. Mine is
rather louder than a relay.

--
*Just remember...if the world didn't suck, we'd all fall off*

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
From: Sansui Samari on 2 Feb 2010 03:17
On Feb 1, 7:08 am, "Dave Plowman (News)" <d...(a)davenoise.co.uk> wrote:
> In article <hk6ovs$rb...(a)usenet01.srv.cis.pitt.edu>,
>    GregS <zekfr...(a)zekfrivolous.com> wrote:
>
> > >Battery operated thermostats don't have a conventional relay - ie one
> > >which takes power all the time it's made. That would run down the
> > >battery in short order. They use some form of 'motorised' switch, which
> > >only takes power when it changes state. On mine you can hear it operate.
>
> > I always assumed a relay, and yes they are loud. On a soild state unit I
> > could also hear a click, but I think that was from current flow. If
> > units use a switch, I hope they have a safety overheat breaker.
>
> Certainly in the UK it's a form of mechanical switch. It can carry mains
> or low voltage AC or DC - not really possible with a solid state device.
> My guess is it may be piezo operated. But that's only a guess. Mine is
> rather louder than a relay.
>
> --
> *Just remember...if the world didn't suck, we'd all fall off*
>
>     Dave Plowman        d...(a)davenoise.co.uk           London SW
>                   To e-mail, change noise into sound.

There are solid state relays that will supply fairly high current at
240vac with a 24vdc switching voltage. They are very common on
automated machinery, I'm not sure if they would be used in a
thermostat, the ones we use are pretty spendy. You can get ones that
are latched, and will only need a signal to change state. Some of the
cheaper digital thermostats that I have installed in rental properties
never make a sound. I've never really had to back engineer one
though, if it fails and I don't have voltage coming through, then I
toss it and get another. Of coarse, if you have a higher end
thermostat then that may not be the thriftiest way to go.

When I test...
-I test to make sure I have a 24vdc supply at the thermostat, by
checking for potential across the wires incoming wires with the
thermostat off. This doesn't work all of the time, if there is a
broken wire or a burnt out relay or fuse, or a bad ground.
-Then check the voltage drop again after the thermostat is supposedly
engaged
-If that's good, check the voltage of the thermostat leads at the
furnace or boiler or whatever. This can be dangerous if you don't
know what you are doing. Usually there is a point on the outside of
the furnace where you can tie in to test the wires.

The rest depends on the end piece of equipment that the thermostat
runs. On many furnaces now, the controller will flash a code if there
is a detectable failure, kind of like the computer in a modern car.
So that's something to consider as well.

-J
From: Dave Plowman (News) on 2 Feb 2010 04:30
In article
<84aa8781-abb4-4902-a17c-8ab2c300fc9e(a)k36g2000prb.googlegroups.com>,
Sansui Samari <jimjam1942(a)gmail.com> wrote:
> > Certainly in the UK it's a form of mechanical switch. It can carry
> > mains or low voltage AC or DC - not really possible with a solid state
> > device. My guess is it may be piezo operated. But that's only a guess.
> > Mine is rather louder than a relay.


> There are solid state relays that will supply fairly high current at
> 240vac with a 24vdc switching voltage. They are very common on
> automated machinery, I'm not sure if they would be used in a
> thermostat, the ones we use are pretty spendy.

Thing is in the UK it was pretty common to have mains to a mechanical
thermostat. Which also supplied an accelerator coil round the bi-metallic
strip to improve accuracy. So aftermarket types can all handle this. On my
last system here everything electrical was mains - gas valve, pump, three
way valve, room stat and water stat. A very simple system which worked
well for years. I've replaced the boiler with a condensing type which has
electronics so has to have a low volt supply for that. But uses sensors
instead of thermostats for house and water temperature which is now set
via the programmer, rather than locally.

Aftermarket thermostats will most often be fitted to older systems here -
so have to cope with either AC mains, or low volt AC or DC. Which I'd
guess rules out a solid state switch.

But even a solid state switch will take some current when made - does it
not? So not ideal for battery operation.

The programmable thermostat I retro-fitted to the old system - allowed you
to set different temperatures for parts of the day and days of the week -
used four AAs for everything - no power from the line - and they lasted
about 2 years. They are a very worthwhile addition to an older system.

--
*Also too, never, ever use repetitive redundancies *

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
From: Geo on 2 Feb 2010 09:02
On Tue, 02 Feb 2010 09:30:13 +0000 (GMT), "Dave Plowman (News)"
<dave(a)davenoise.co.uk> wrote:


>The programmable thermostat I retro-fitted to the old system - allowed you
>to set different temperatures for parts of the day and days of the week -
>used four AAs for everything - no power from the line - and they lasted
>about 2 years. They are a very worthwhile addition to an older system.

Sounds a bit like my Danfoss TP75. It uses an Omron latching relay type
G6CK-2117P which works off a 20mS 3V pulse:-
http://www.omron.com/ecb/products/pry/121/g6c_2.html


--
Geo
From: Dave Plowman (News) on 2 Feb 2010 09:54
In article <lvbgm5l9qavb1v2gjkck2sj2m945a5udel(a)4ax.com>,
Geo <hw9j-s5hw(a)dea.spamcon.org> wrote:
> >The programmable thermostat I retro-fitted to the old system - allowed you
> >to set different temperatures for parts of the day and days of the week -
> >used four AAs for everything - no power from the line - and they lasted
> >about 2 years. They are a very worthwhile addition to an older system.

> Sounds a bit like my Danfoss TP75. It uses an Omron latching relay type
> G6CK-2117P which works off a 20mS 3V pulse:-
> http://www.omron.com/ecb/products/pry/121/g6c_2.html

Interesting - but nothing like those on my board. I no longer have it so
can't take pics. The description isn't that clear - does it take (near)
zero current when made or just a reduced amount? For long battery life it
would need to be zero. Nor did the noise it made when the 'switch'
operated sound anything like a relay.

--
*I don't suffer from insanity, I enjoy every minute of it *

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