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-   -   DIY temp controller build (http://www.homebrewtalk.com/f51/diy-temp-controller-build-133364/)

android 08-22-2009 11:51 PM

DIY temp controller build
EDIT: the project is now finished and you can find the pictures of the completed project on page 3.

well, after much deliberation, i decided to just build a temp controller myself... i know there are probably benefits from just getting a love/johnson/ranco, but i like building stuff, so that was justification enough for me to give it a whirl. i based the project off this persons plans.
all i have left to do is wait for the SSR from ebay to arrive and i will be able to hook up the wires, plug in the fridge and go. i will update with more photos of the SSR hookup when it comes.

parts list:
1 hunter thermostat - $20 (walmart)
1 spool soldering wire - 3$ (radioshack)
1 solid state relay - $7 (ebay)
- min 10A, mine is 25A
- 3-32 vdc supply
- 24-480V AC load
1 pack heat shrink tubing - $2 (lowes)
old telephone cord
old extension cord - plug part
small piece of thermostat wire
old DC converter plug from who knows what (3-32 vdc)
job box - $3 (lowes)
cover plate - $1 (lowes)
15A receptacle - $2 (lowes)

approximately $38 if you have some extra stuff lying around, maybe even less if you do it right.

here's the thermostat i got:


step #1: take off back, finagle out the circuit board by removing all screws with an arrow next to them and freeing battery terminals with a screwdriver or something small. there is one screw hiding beneath the furthest left little circular blue resistors or whatever they are


step #2: use soldering iron to desolder the thermistor (just hold the solder end up to the tip of your gun until it liquefies and you can pull out the wire one side at a time) i was pretty worried about the fragility of the thermistor but it turns out they are pretty tough (DAMHIKT). then, solder a piece of speaker wire or telephone wire into where the thermistor used to be. now, solder the thermistor on the end of the wire lead. use some heat shrink on each individual thermistor wire and then a larger piece on top of the separate wires, it'll look something like this when done:




android 08-23-2009 12:12 AM

step #3: route the new remote thermistor through the housing of the thermostat and test it out.


close enough for government work.

step #4: wire up the box/receptacle/power plug according to the wire diagram (i would post the diagram, but the other guy technically did it, so look at it in his post for clarification)



step #5: connect DC plug and wire to SSR to appropriate terminal on thermostat (according to diagram)


step #6: connect wires to SSR (not done yet, 10-15 days away)

step #7: mount it all up to the job box and fire away.


i'm no expert in electrical tinkerings by any stretch of the imagination. if i can do it, so can you. any questions, feel free to shoot. like i said, i'll update innards pics with the SSR hooked up when it arrives.

Sagan 08-23-2009 05:24 AM

What's the model number on the thermostat? I can't seem to find it on Wally World's website.

Brewers Hardware 08-23-2009 05:34 AM

I've converted quite a few of the $23 thermostats from HomerDepot. One thing that I've found helpful is to clip the thermistor wires about 1/4" to the circuit board and then solder the extension wire to those protruding wires. I destroyed one thermostat because it was being a real bitch and I applied too much heat and popped the traces off the circuit board... oops. Leaving the short wires gives you something easier to solder too.

Just my .02

Nice job on the conversion

android 08-23-2009 04:09 PM

model 42995B is what it says on the package... but inside the back cover it says 42999B, so i'm not 100% sure what it is.

Jarontea 08-23-2009 07:24 PM

I was thinking of doing something just like this. Would this be able to control 2 units (Heater/Fridge)? Would you then need a second set of everything but the Thermostat?

passedpawn 08-23-2009 09:22 PM

Johnson Controllers (A19 type) can be had from ebay for < $30. That's where I bought mine. You do have to supply your own power cord, but that's it.

android 08-24-2009 02:29 AM


Originally Posted by Jarontea (Post 1502386)
I was thinking of doing something just like this. Would this be able to control 2 units (Heater/Fridge)? Would you then need a second set of everything but the Thermostat?

i'm pretty sure it's possible, but i just plan to keep the jumper wire in place and switch it over to heat when i need it. i assume there will be a period of time when i need both, but i'll just use my basement to ferment in until i can just use the heating.

ftlstrings 08-24-2009 02:40 AM

Nice work! This looks very well laid out, and simple.


Mike. http://www.homebrewtalk.com/images/smilies/drunk4zc.gif

salad 419 08-26-2009 10:06 PM

Just a couple of quick questions...

How low can you set that thermostat?
Do you have to modify it in any way to get to 33 degrees?
It just seems that most I've seen only go down to 55 degrees.


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