DIY temp controlled fermentation chamber from broken fridge.

(reposted from last year from Homebrewtalk)

So a couple weeks ago, my fridge broke. Since I live in an apartment, the landlord had a new one brought

3 flights of stairs by his crew. I saw an opportunity in this as it took those guys around 20 minutes to bring the new one up. I asked them if I could keep it and they said "sure go ahead." I now had this dead fridge out in my 30º sun room that I needed to get working on. I already had a thermostat in my closet, but the closet has been proving too leaky to keep at a reasonable temp. So it worked out really well. 

 

Here's what I did. 

I went to home depot to get a soldering iron so I could start piecing this thing together with my old Honeywell classic mercury thermometer. On the clearance rack, there was a Honeywell non-programmable digital thermostat for $15 from $30. Score!

I proceeded to tear it apart so I could move the thermistor inside the fridge. If I had the option, I didn't want to have to open the fridge to check or change the temp.

Getting the thermistor off was easy, I had a hard time getting it back on as I had no way to remove the old solder so I couldn't get the leads through easily and when they did punch through, they took the solder pads with them. I also need more practice on smaller things, I'm used to soldering larger things like PA speakers and cables

After adding the jumper to the thermistor, I punched some holes in the fridge and ran the cable outside.

My roommate Gigawatts and I had built a control box type thingy with an older thermostat to keep the closet warm while out of town so we just adapted it to this build. It contains a 12V wall adapter, a 12V relay, a male IEC connector (like on your computer power supply) and a standard Edison plug for whatever 120V appliance we wanted to switch. I added an ethernet port to the back of it so it didn't have to be hard wired into my thermostat.

Since this fridge was outside essentially and temps were dropping into the 20's, the batteries weren't holding out so we used one of the spare pairs in the ethernet cable to send 3V to the thermostat so the batteries were no longer needed. The 12V to 3V circuit is in the bottom left of the box, near the blue tape.

For heating the fridge, I had planned on using the defrost element from the evap coil in the freezer, but at 450 watts, it was creating an extremely hot layer at the top of the fridge and I was getting temp swings of 12º as it started mixing down. I am looking for a small 120V fan that I could stick in there to mix things up, but until then, I will be using a 100 watt incandescent lamp. Its still plenty powerful to keep the fridge warm, but I would feel better with something that wont shatter if it gets wet or something. This is what I ended up with. It will probably hold 2 standard ale pails, but the fermenter in there now is quite a bit wider and shorter than my other fermenters.