thermostat to run light bulb or small heater to prevent freezing

[paulcalif]

Hi folks,
I can solder, and I can find parts. I know electrical, but just a little electronics. I can read a diagram and I can build a circuit if I know what parts to use.

This is what I want to do, and I need your help.

I have a well room and a pump room. Temperaturs can get down below freezing. When the temperaturs approach freezing, I would like a small heater to come on or a light bulb (which ever will do the job). This is just to keep the temperature in the small rooms above freezing so the pipes don't burst.

Since I will be building it myself, I guess I should plan on it controlling 20 amps. I doubt that there are any 120V heaters that use more than that right?

It should come on at say 34 degrees and off at something slightly higher, 36???

Simple is probably better. I just built a Solid State Relay circuit that controls my 220V well pump. It's awesome.

Thanks in advance.

 

[KMoffett]

If you want to do a kit: http://store.qkits.com/moreinfo.cfm/FK934
Looks like the relay is rated for 7A@250VAC.

Ken

 

[paulcalif]

That's pretty cool, and I like the price. I suppose I could have it control another relay. I would prefer a 120V design/kit however as this one is 12v . Thanks for the quick reply!!

 

[KMoffett]

Just a 120VAC-12VDC wall wart to power it. If you need to control higher currents, you could add an outboard relay or SSR.

Ken

 

[paulcalif]

Wall Wart - LOL - I asume you mean a little plug in power supply. I got a ton of them, but not sure I have any more 12V. I'm sure they are very easy to come by. Thanks again Ken. I may go this route.

Paul

 

[KMoffett]

I finally found the current consumption for the circuit...50mA. So any 12VDC "wall plug transformer" rated for higher current than that should work.

Ken

 

[JimW]

Just buy one and save the trouble. Google: "portable thermostat". Northern tool has one for $50. Plug it into the AC, then plug the heater/lamp/whatever into the output socket.

-Jim

 

[KMoffett]

Cool! Another one...cheaper...but, may not be with shipping.

Ken

 

[ChosunOne]

Paulcalif, I'd recommend you set the thermostat to turn on the heater considerably higher than a couple of degrees above freezing---there's usually a substantial time lag between the heater starting up and the room temperature being affected, depending on the size of the room and how airtight and insulated it is. Also, it's generally a good idea to leave a little margin of error. 34 to 36 is cutting it awfully close. I'd go with _at least_ 40 F.

Given that a failure is going to be very expensive, you might even consider some kind of warning alarm to alert you the temp is going under your bottom temperature---it would be silly to pay $500+ in damage because a $20 heater failed. An incandescent light bulb makes a good heater for a small space (about 95% efficient), but keep in mind that those bulbs sometimes burn out unpredictably. As to electric heaters, if less often.

 

[KMoffett]

Also, there are temperature gradients in a space with calm air...colder at the floor.

Ken