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Odd central heating problem - relay or thermostat switching

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Gefreiter Krueger
Guest

Sun Nov 24, 2013 12:48 am   



When I moved in 13 years ago, there was a central heating system utilising only radiator stats. I fitted a room thermostat (the basic bi-metallic strip variety), which connected live to the motorised valve, which in turn switched on the pump and boiler. For some reason, it would often arc when switching off, which heated the bi-metallic strip up a little and it never managed to go off. Problem solved by using an electronic thermostat which contained a relay, causing cleaner switching.

Similar problem now, with the heating system extended so it does the garage, aswell as the house, with a seperate electronic thermostat. The problem this time though, is because I could only find a motorised valve for the garage which did not have contacts inside it (only one which fitted my odd diameter of pipe), I had to fit a relay to switch the boiler and pump on and off (if I'd connected the output of the garage stat straight to the pump, boiler, and valve, then the valve would open every time the boiler and pump ran for the house too). Anyway, it worked fine for a year, then the relay started behaving like the old bi-metallic strip thermostat - it arced when switched off, and took ages to do so, making an alarming noise. So I replaced the relay with a big industrial contactor which is working for the moment. The relay I replaced says it can take up to 2HP motors, way more than my pump. Any idea what's going on?

--
The record of having had intercourse the most frequently goes to a boy who was recorded to have had intercourse about 52,000 times over a period of 30 years. This means he had intercourse on average 33.3 times a week.

harryagain
Guest

Sun Nov 24, 2013 2:44 pm   



"Gefreiter Krueger" <no_at_spam.com> wrote in message
news:op.w60jrhnjiunomv_at_red.lan...
Quote:
When I moved in 13 years ago, there was a central heating system utilising
only radiator stats. I fitted a room thermostat (the basic bi-metallic
strip variety), which connected live to the motorised valve, which in turn
switched on the pump and boiler. For some reason, it would often arc when
switching off, which heated the bi-metallic strip up a little and it never
managed to go off. Problem solved by using an electronic thermostat which
contained a relay, causing cleaner switching.

Similar problem now, with the heating system extended so it does the
garage, aswell as the house, with a seperate electronic thermostat. The
problem this time though, is because I could only find a motorised valve
for the garage which did not have contacts inside it (only one which
fitted my odd diameter of pipe), I had to fit a relay to switch the boiler
and pump on and off (if I'd connected the output of the garage stat
straight to the pump, boiler, and valve, then the valve would open every
time the boiler and pump ran for the house too). Anyway, it worked fine
for a year, then the relay started behaving like the old bi-metallic strip
thermostat - it arced when switched off, and took ages to do so, making an
alarming noise. So I replaced the relay with a big industrial contactor
which is working for the moment. The relay I replaced says it can take up
to 2HP motors, way more than my pump. Any idea what's going on?


Arcing is caused by stored emergy in the system (usually coils/electric
motors.)
You will often get a tiny spark when switching motors, this is normal and
not enough to affect a bimetal strip.
Most switches have a "snap action" to minimise this.
Just what do you mean by arcing?

Dave Liquorice
Guest

Sun Nov 24, 2013 3:31 pm   



On Sat, 23 Nov 2013 17:48:43 -0000, Gefreiter Krueger wrote:

Quote:
Anyway, it worked fine for a year, then the relay started behaving like
the old bi-metallic strip thermostat - it arced when switched off, and
took ages to do so, making an alarming noise.


Bi-metalic thermostats are renown for not operating quickly and
sitting there partially open with and arc sometimes for many seconds.
Sort of surprised a mains relay has developed what appears to be the
same problem, maybe the small, inevitable, arc when switch a motor
has damaged the contacts sufficiently for the gap not to be large
enough quick enough to break the arc and it damages the contacts even
more...

When switching reactive loads, like motors, you need to look at the
spec of your relay to see how badly it is derated. Contacts rated for
240 V AC 10A resistive load may well fall to 1 A with reactive loads.

--
Cheers
Dave.

Brian Gaff
Guest

Sun Nov 24, 2013 4:23 pm   



I have seen so called snubber networks across motors and when I asked they
told me it reduced sparking on switch overs, but whenpressed to explain they
were more vague, but certainly you will get a pulse after disconnection of
any inductive load.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"harryagain" <harry130747_at_btinternet.com> wrote in message
news:l6saph$l44$9_at_dont-email.me...
Quote:

"Gefreiter Krueger" <no_at_spam.com> wrote in message
news:op.w60jrhnjiunomv_at_red.lan...
When I moved in 13 years ago, there was a central heating system
utilising only radiator stats. I fitted a room thermostat (the basic
bi-metallic strip variety), which connected live to the motorised valve,
which in turn switched on the pump and boiler. For some reason, it would
often arc when switching off, which heated the bi-metallic strip up a
little and it never managed to go off. Problem solved by using an
electronic thermostat which contained a relay, causing cleaner switching.

Similar problem now, with the heating system extended so it does the
garage, aswell as the house, with a seperate electronic thermostat. The
problem this time though, is because I could only find a motorised valve
for the garage which did not have contacts inside it (only one which
fitted my odd diameter of pipe), I had to fit a relay to switch the
boiler and pump on and off (if I'd connected the output of the garage
stat straight to the pump, boiler, and valve, then the valve would open
every time the boiler and pump ran for the house too). Anyway, it worked
fine for a year, then the relay started behaving like the old bi-metallic
strip thermostat - it arced when switched off, and took ages to do so,
making an alarming noise. So I replaced the relay with a big industrial
contactor which is working for the moment. The relay I replaced says it
can take up to 2HP motors, way more than my pump. Any idea what's going
on?


Arcing is caused by stored emergy in the system (usually coils/electric
motors.)
You will often get a tiny spark when switching motors, this is normal and
not enough to affect a bimetal strip.
Most switches have a "snap action" to minimise this.
Just what do you mean by arcing?




Gefreiter Krueger
Guest

Sun Nov 24, 2013 7:15 pm   



On Sun, 24 Nov 2013 07:44:52 -0000, harryagain <harry130747_at_btinternet.com> wrote:

Quote:

"Gefreiter Krueger" <no_at_spam.com> wrote in message
news:op.w60jrhnjiunomv_at_red.lan...
When I moved in 13 years ago, there was a central heating system utilising
only radiator stats. I fitted a room thermostat (the basic bi-metallic
strip variety), which connected live to the motorised valve, which in turn
switched on the pump and boiler. For some reason, it would often arc when
switching off, which heated the bi-metallic strip up a little and it never
managed to go off. Problem solved by using an electronic thermostat which
contained a relay, causing cleaner switching.

Similar problem now, with the heating system extended so it does the
garage, aswell as the house, with a seperate electronic thermostat. The
problem this time though, is because I could only find a motorised valve
for the garage which did not have contacts inside it (only one which
fitted my odd diameter of pipe), I had to fit a relay to switch the boiler
and pump on and off (if I'd connected the output of the garage stat
straight to the pump, boiler, and valve, then the valve would open every
time the boiler and pump ran for the house too). Anyway, it worked fine
for a year, then the relay started behaving like the old bi-metallic strip
thermostat - it arced when switched off, and took ages to do so, making an
alarming noise. So I replaced the relay with a big industrial contactor
which is working for the moment. The relay I replaced says it can take up
to 2HP motors, way more than my pump. Any idea what's going on?


Arcing is caused by stored emergy in the system (usually coils/electric
motors.)
You will often get a tiny spark when switching motors, this is normal and
not enough to affect a bimetal strip.
Most switches have a "snap action" to minimise this.
Just what do you mean by arcing?


For the first one, interference on radios and TV. When I stand in the same room as the thermostat, I can hear the spark continuously inside it. It warms the strip up and the thermostat never goes off as a result.

With the second one, the relay is juddering and making a fucking racket. The digital thermostat in the garage is still making a funny smell after changing the relay inside it and the one in the loft that it switches. I suspect the electronics are fucked, it is damp out there. I don't think there was anything wrong with either relay, just buggered electronics through damp. So the only inductive problem was the first one. I tried about 5 different makes of stat and they all did the same, I guess my pump's snubber is broken, but realys can handle it as they switch quicker.

--
The microwave was invented after a researcher walked by a radar
tube and a chocolate bar melted in his pocket.

Gefreiter Krueger
Guest

Sun Nov 24, 2013 8:56 pm   



On Sun, 24 Nov 2013 13:31:49 -0000, Dave Liquorice <allsortsnotthisbit_at_howhill.com> wrote:

Quote:
On Sat, 23 Nov 2013 17:48:43 -0000, Gefreiter Krueger wrote:

Anyway, it worked fine for a year, then the relay started behaving like
the old bi-metallic strip thermostat - it arced when switched off, and
took ages to do so, making an alarming noise.

Bi-metalic thermostats are renown for not operating quickly and
sitting there partially open with and arc sometimes for many seconds.
Sort of surprised a mains relay has developed what appears to be the
same problem, maybe the small, inevitable, arc when switch a motor
has damaged the contacts sufficiently for the gap not to be large
enough quick enough to break the arc and it damages the contacts even
more...

When switching reactive loads, like motors, you need to look at the
spec of your relay to see how badly it is derated. Contacts rated for
240 V AC 10A resistive load may well fall to 1 A with reactive loads.


The inductive rating of the relay is well above that of the motor. Anyway, I've decided the relays are fine, it's the electronics that's buggered in the thermostat. I blast the floor clean in there (it's converted to a parrot room) with a jetwash every week. I guess the damp mist from it has knackered it.

--
My younger sister was having one of her first gynecological appointments and she had some questions for the doctor.
"Doctor" she asked, "I can't ask my parents, They would kill me but my boyfriend wants to have anal sex. I don't know what to tell him, I mean I don't know anything about it. Can I get pregnant?"
The kindly old doctor smiled whimsically and replied "Of course, you can my dear. Where do you think lawyers come from?"

fred
Guest

Sun Nov 24, 2013 9:14 pm   



In article <op.w60jrhnjiunomv_at_red.lan>, Gefreiter Krueger <no_at_spam.com>
writes

Quote:
Any idea what's going on?

You may get more help if you re-post using one of your less troll
related sock puppets.
--
fred
it's a ba-na-na . . . .

Gefreiter Krueger
Guest

Sun Nov 24, 2013 9:24 pm   



On Sun, 24 Nov 2013 14:14:09 -0000, fred <not_at_for.mail> wrote:

Quote:
In article <op.w60jrhnjiunomv_at_red.lan>, Gefreiter Krueger <no_at_spam.com
writes

Any idea what's going on?

You may get more help if you re-post using one of your less troll
related sock puppets.


Trolling is in the eye of the beholder.

--
101 Dalmatians and Peter Pan are the only two Disney animated features in which both the parents are present and don't die throughout the movie.

Dave Liquorice
Guest

Mon Nov 25, 2013 11:03 am   



On Sun, 24 Nov 2013 12:15:31 -0000, Gefreiter Krueger wrote:

Quote:
For the first one, interference on radios and TV. When I stand in the
same room as the thermostat, I can hear the spark continuously inside
it. It warms the strip up and the thermostat never goes off as a
result.


Think you have the logic inverted there. If the arc is warming the
strip it ought to be forcing the contacts open, off, satisfied not to
closed, on, call for heat that requires a cooler strip.

> I guess my pump's snubber is broken,

Don't think I've ever seena a pump with a snubber network. They are
normally fitted at the switch not the reactive load.

--
Cheers
Dave.

Gefreiter Krueger
Guest

Mon Nov 25, 2013 6:42 pm   



On Mon, 25 Nov 2013 09:03:54 -0000, Dave Liquorice <allsortsnotthisbit_at_howhill.com> wrote:

Quote:
On Sun, 24 Nov 2013 12:15:31 -0000, Gefreiter Krueger wrote:

For the first one, interference on radios and TV. When I stand in the
same room as the thermostat, I can hear the spark continuously inside
it. It warms the strip up and the thermostat never goes off as a
result.

Think you have the logic inverted there. If the arc is warming the
strip it ought to be forcing the contacts open, off, satisfied not to
closed, on, call for heat that requires a cooler strip.


Ah, my bad memory. The problem was it couldn't switch the heating on. As the room cooled, the contacts tried to close, and just as they were closing there was an arc and it caused the strip to warm up and bend away again. It would be intermittent at first, then as the room got even colder it became continuous.

Quote:
I guess my pump's snubber is broken,

Don't think I've ever seena a pump with a snubber network. They are
normally fitted at the switch not the reactive load.


The switch? The thermostat is the switch.

--
Why did kamikaze pilots wear helmets?

Gefreiter Krueger
Guest

Fri Nov 29, 2013 1:03 am   



On Sun, 24 Nov 2013 13:31:49 -0000, Dave Liquorice <allsortsnotthisbit_at_howhill.com> wrote:

Quote:
On Sat, 23 Nov 2013 17:48:43 -0000, Gefreiter Krueger wrote:

Anyway, it worked fine for a year, then the relay started behaving like
the old bi-metallic strip thermostat - it arced when switched off, and
took ages to do so, making an alarming noise.

Bi-metalic thermostats are renown for not operating quickly and
sitting there partially open with and arc sometimes for many seconds.
Sort of surprised a mains relay has developed what appears to be the
same problem, maybe the small, inevitable, arc when switch a motor
has damaged the contacts sufficiently for the gap not to be large
enough quick enough to break the arc and it damages the contacts even
more...

When switching reactive loads, like motors, you need to look at the
spec of your relay to see how badly it is derated. Contacts rated for
240 V AC 10A resistive load may well fall to 1 A with reactive loads.


Damnit! Rats! Nothing wrong with either relay or the thermostat. Wire between garage and house (live/switched live to thermostat) presumably chewed and half shorting. I think they got into the underground conduit from the garage. Always use armour plated cable underground, plastic trunking no good if open at one end!

--
Trading standards have removed the gollywog from Robinsons marmalade jars,
not due to racism but because Niggers were using the labels as bus passes!

Gefreiter Krueger
Guest

Fri Nov 29, 2013 1:07 am   



On Thu, 28 Nov 2013 18:03:11 -0000, Gefreiter Krueger <no_at_spam.com> wrote:

Quote:
On Sun, 24 Nov 2013 13:31:49 -0000, Dave Liquorice <allsortsnotthisbit_at_howhill.com> wrote:

On Sat, 23 Nov 2013 17:48:43 -0000, Gefreiter Krueger wrote:

Anyway, it worked fine for a year, then the relay started behaving like
the old bi-metallic strip thermostat - it arced when switched off, and
took ages to do so, making an alarming noise.

Bi-metalic thermostats are renown for not operating quickly and
sitting there partially open with and arc sometimes for many seconds.
Sort of surprised a mains relay has developed what appears to be the
same problem, maybe the small, inevitable, arc when switch a motor
has damaged the contacts sufficiently for the gap not to be large
enough quick enough to break the arc and it damages the contacts even
more...

When switching reactive loads, like motors, you need to look at the
spec of your relay to see how badly it is derated. Contacts rated for
240 V AC 10A resistive load may well fall to 1 A with reactive loads.

Damnit! Rats! Nothing wrong with either relay or the thermostat. Wire between garage and house (live/switched live to thermostat) presumably chewed and half shorting. I think they got into the underground conduit from the garage. Always use armour plated cable underground, plastic trunking no good if open at one end!


Although that doesn't explain the burning smell from the thermostat, which has no damage inside it.

--
For 93 million miles, there is nothing between the sun and my shadow except me. I'm always getting in the way of something...

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