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intermittent non-appliance timer to open/close low vote circuit

intermittent non-appliance timer to open/close low vote circuit

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Old 12-28-07, 02:46 PM
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intermittent non-appliance timer to open/close low vote circuit

I have a gas fireplace on a low volt thermostat.

I want to shut if on and off every 20 minutes or so cause I think it becomes less efficent to keep on the fire once it is hot - so I want some in-between time for it to cool down a bit.

I am looking for a timer similiar to a light timer that has all the pins you can set - but when it's on I don't want to be sending 110 volts through the connection - I just want the on to close the circuit and the off to open it - or vice-versa - whatever the case.

I don't know the proper term for it so it has been hard to search for.
 
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Old 12-28-07, 07:44 PM
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The term would be "dry contact" timer.

if you cannot find one, you can rig up what you need with a small 12v wall wart supply and an automotive relay, with the supply connected to normal timer.
 
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Old 12-29-07, 06:52 AM
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Search for "timed relay". This example is pricey, but has two different settings for on time and off time.
 
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Old 12-29-07, 09:37 AM
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Thanks.

I thiink I understand - hook timer to 12 volt transformer that connects to automoitve relay - makes sense.

Is there anything particular I should loo for in a automotive relay ? I am assuming when voltage is applied that it closes a switch while applying no voltage through it.
 
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Old 12-29-07, 10:30 AM
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Although you specifically asked an electrical question operating your fireplace the way you propose is counter productive.

If the fireplace has a chimney it will not heat the chimney enough and could cause the flue gasses to condense.
You might wind up with water collecting at the base of the chimney or in the fireplace.
If it is a ventless unit you could wind up with it giving off more products of combustion each time it starts up.

Another problem is that if you have a standard low voltage heating thermostat they use a heat anticipator which is energized each time the burner is cycled off.
If you cut the power to the thermostat the heat anticipator will not operate and you will experience wide temperature swings which will cancel out any savings from cycling the burner on a timer.
 
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Old 12-29-07, 12:39 PM
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Thanks for those comments. I was somewhat concerrned that the whole process would be counter productive more from a btu perspective - as I understand it a btu is a btu - so it has to be going someplace. But as I was noticing that once the metal and front glass gets to a certain heat emitting stage, it just seems like it didn't keep getting hotter - even if the flame was still going (as the thermostat was still calling for heat.) And so I would experiment and turn off the thermostat for 10 minutes or so - and it seemed like heat kept on emitting pretty strongly from the glass and metal - so that's when I thought maybe an intermittent on/off type system might be more efficient. But in the back of my mind the btu=btu throught was there - but I was thinking perhaps the extra btu's were going out the flue rather into the room.

Anyway - the gas fireplace has a dual chamber flue that rises 4' and then 90 bends to vent outside. Never seen condensation anyplace when the fireplace goes on and off regulated by the termostat - but certainly will keep an eye on that.

The thermostat is a .15 amp Lux that is powered by I believe the thermocouple - so it should power up pretty quickly once it gets the connection - even if it is not getting it constantly from the thermocouple - at least I would think that.

I actually have a dual on/off switch - I can either have the fireplace gas on all the time - or I can switch it to thermostat and have that control the on/off.
 
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Old 01-01-08, 04:40 PM
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One question about the automotive relay - is that just an open circuit - with no power on the line - with the 12 volt causing it to stay open or closed ?

And it seems like there are several available - does it matter which one ?
 
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Old 12-14-09, 03:05 PM
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One mroe time

Well - I never got this one solved - but this is what I want to happen.....

When the stove heats up, after it gets to a certain temperature, a temperature switch turns on a 110 volt blower fan.

I want the gas flow (not the pilot) to shut down when the fan comes on, and to stay off till the fan shuts off, which it will do when the stove cools down.

So I think I need a NC dry contact switch that opens when power is supplied (by a transformer).

I get wiring in a transfomer to the fan so the transformer comes on when the fan comes on.

I don't get where to find a NC dry Contact switch, which may well be an automotive relay. Would one look for a NC automotive relay switch ?

Idealy, it would be nice to have a 10 minute delay between the time the fan supplies the power to the transformer and the time the NC switch goes open (off).
 
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