Today I did the hardware modification and brewed some beer at the same time.
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http://www.albumonline.net/display.php?id=daaec33c - fridge and pi pic)
I started by taking the top off the fridge so I could see if I could easily make a hole in it without actually destroying the cooling lines. After a fair bit of scraping I discovered the top of the fridge and no cooling lines. Because the top of the fridge was raised off the foam, I was able to mount XLR chassis mounts on the side of the fridge. I'll still need to fill the holes where the sensor cables went, but it's no big problem.
Having done this we attached the heating element. I've used an old brew belt which I was given 10 years ago and have used twice. I stripped off the plug, soldered the ends of this and the wires we'd run into the fridge together and used cable shrink wrap to make it watertight as possible.
The fridge itself, I just snipped the wires from the compressor and control it direct. This means I loose the light but I'm not that bothered. The fridge plug became the plug for the SSRs.
What was a bit odd was the plug socket had a 13A fuse, yet the fridge only used about 0.6A. Seems a bit silly to me.
On each of the hot lines we put an inline fuse.
SSRs were rated at 10A. Though as the circuit will only be drawing a tiny amount, I doubt they'll ever be needed.
We mounted the SSRs in a plastic project box and connected up to the brewpi.
Had a small hardware issue with connecting the sensors. Red = 5v/Live obviously. Thought the blue was the neutral and the black was the control/sensor cable. Turns out I was very much wrong. Was infact the other way round. No problem, switched the cables round and all worked. Shame it took over two hours to work that out.
Once the sensors were working it was possible to run the heating/cooling elements and test. I used the fridge temperature to control, setting to 9 to start with then putting it back up to the outside ambient temp of about 13. I'm going to leave it running overnight and see if burns down the garage. Then I'm going to use my bottle bucked and thermowell to test the temperature control with a beer profile (eg 20'C for 3 days, 16 for 4, 20'C for 3 then crash cool)
Brewpi screen of first test.
http://www.albumonline.net/display.php?id=3f6ae954