Swapping fridge thermostats

I know I will probably get some, "Just buy a temp controller" comments, but this is worth a shot anyways....

I am about to start construction on my fermentation cabinet (https://www.homebrewtalk.com/showthread.php?t=54562) and I would like to replace the thermostat in a fridge with a standard digital house thermostat (which I already have). I know it may be a pain in the butt to do, but anyone have any ideas? The wiring diagram looks like the thermostat acts as a switch in series with the compressor, and the voltage/amps on the circuit are probably too high for the household thermostat, and trying to run it in parallel won't switch the compressor on and off. I am sure a relay would do the trick, but I only know enough about electronics to follow a schematic, not really enough to design a circuit that would be safe.

Anyways, shot in the dark, if anyone would like to toss out some ideas, I would be more than willing to build it.

A house thermostat, a DC power supply, and a relay would add up to being about the same price as a controller.

Bobby_M said:

A house thermostat, a DC power supply, and a relay would add up to being about the same price as a controller.

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Just buy a temp controller comment #1, thanks Bobby


You are 100% right, but I already have the thermostat (bought two when I thought I was just going to do my cabinet with ice bottles) and the power supply (a computer power supply I already have rigged to run some fans in my chiller) I have the fridge for free and would like to incorporate it so I do not have to change ice bottles. All I am really missing is the relay, and I can probably pick one up at the local radio shack If I cant scrounge the right one from something broken around the house.

Plus, this way I get to build something, and don't have the tell tale box lying around that tells SWMBO that I ordered something for beer again

Bump?

Anyone got ideas on the type of relay I should use, anything else I should add in, or something I am forgetting? Would something like this do the trick, or am I barking up the wrong tree and just looking to burn my house down.....

Ok, so you need to check that the contacts on the thermostat for cooling is just a simple single pole or make/break switch. If that's the case, you run 12v DC to the coil of a relay (you need one specifically that takes 12vDC on the coil) but you interrupt the 12v circuit with the thermostat. That same relay has to be able to support the 120v that will run to the fridge at whatever the current rating is (probably 15amp).

Awesome thanks Bobby!

I found a relay at radio shack this morning for ~$5, and this is it up and running right now:


I know it looks like a mess, but I will clean it up when I start tearing apart the fridge and building my chiller. This was a lot simpler that I was imagining for some reason.

Thanks for your help!

Finally got enough honey-do's out of the way to get going on this, huh?! :rockin:

jas0420 said:

Finally got enough honey-do's out of the way to get going on this, huh?! :rockin:

Click to expand...

Haha, yep I am playing with the wiring today while painting the room this is going to go into. I am hoping to start the real construction within the next day or two... By the weekend for sure.

By the way, long time no hear! You been keping busy?

I recognize that green wire-clamp. That's a Dell PSU.

Any problems with the relay setup? I am wanting to do the same...temp control for a fridge (it gets too cold for ales) using a house thermostat (looks like yours with a remote thermistor), a 12vdc power adapter and a relay.

Which relay did you use?

Can't remember what relay I used, I just went to the local radio shack and found one with a 12v coil and a 120v switch. its a DPDT, which is more than I needed, but it works.