How to build your own Temperature Controller Box…

One of the many things I love about brewing is that I get to incorporate not only my love of beer, but my love of building things. Making crazy gadgets to suit the task at hand is something I have a lot of fun doing. Thanks to the many great articles written and shared by other home brewers, some gadgets have been tried & tested, with the rest of us benefiting from those who have gone before. This is one such gadget.

As I move deeper into brewing territory, other variables in the beer making process start to come into focus and the time comes to tinker with them to see if we can continue to improve our beer. Fermentation temperature is something that I hear many people talk about. Jamil Zainasheff has gone so far as saying it’s a “game-changer”. Wow, to say that, intrigues me. Up until now, the area of my basement that I use to ferment has a fairly steady temperature of about 68-70F, which is perfect for most ales. At one point last summer, I was fermenting a blonde ale when the compressor on our AC unit crapped out. It ended up fermenting in the 74-75F range, which is fairly high. The beer actually turned out fantastic, but I don’t know how much of a role the higher temperature played in that. Lagers, on the other hand, are different story. You need to have control over your temperatures. Since we’re now brewing 10 Gallon batches, it gives us the opportunity to split the batches into 2 five gallon carboys and try different yeasts, different fermentation temperatures and different dry hopping rates.

One way to gain control over our fermentation temperatures is to build a dedicated fermentation chamber. I lucked out a few weeks back and scored a medium sized chest freezer that someone down the street was tossing out. I suppose you could use a refrigerator, but this is what I have. A chest freezer will also hold more carboys and/or kegs.  (I’m also not certain whether or not a fridge will allow you to get down to the temperatures needed to properly lager (32F-35F), but I could be mistaken.)

So you’ve got your fridge or freezer, now what? We need to override the internal thermostat and give ourselves the ability to dial in the temperatures we want. There are a few ready-to-go temperature controllers available from Johnson Controls and Ranco that seem to do the job well. They will cost you a little bit more up front, and will also cut out any of the fun building your own, but who wants that?  Well, maybe some of you, and that’s totally cool. For me, I like to build stuff, so that’s what I’m going to do.

To get started, we need to source out the following materials:

UPDATE:  Please see my update on how to add a relay into the circuit to make your controller safer and extend it’s life…

** NOTE – the temperature control unit is a great deal, but be aware that it does come from China, so it is going to take some time to get here. Order ahead, and be patient, mine took about 2 months to arrive.

The tools you’ll need to complete this job are:

  • flat head screwdriver
  • phillips screwdriver
  • wire stripper / cutters
  • drill
  • jigsaw

First thing we’re going to need to do is define where we’re going to cut our openings in the front panel of the junction box. What I did was measure out the size of the temperature controller and the size of the faceplate (not the receptacle) and spaced it out evenly and centered on the panel. Then I drew up a template on paper and stuck it on the inside of the panel. (You could probably lay the parts on the front and use a sharp scribe to scratch the perimeter lines on the faceplate as well, (** use the receptacle for this part of it) Drill holes in the corners of the windows, as well as hole for the screws that attach the faceplate and receptacle. Then use a jigsaw to cutout the windows like this:

This is what it looked like from the other side when finished:

You can then insert the temperature controller by removing the two orange side clips, and then reattaching them once it is in place. Also at this time, you can see how your receptacle fits, and make any adjustments. (in case the opening is too small)

Next, you need to drill a 7/8″ hole into one of the sides of the utility box and insert the cable connector like this:

Now on to the wiring. This is the schematic we need to follow:From the romex, cut 3 pieces of approximately 6 inches each, and remove the outer insulation. You’ll need 3 pieces of the ‘white’ wire, and 2 pieces of the black wire. Use your wire strippers to remove about 3/8″ -1/2″ of insulation on each end.

Next, take 2 of the white wires and  connect one of them to the #2 outlet (see diagram above) on the temperature controller unit. Connect the other to one of the ‘silver’ screws on the duplex receptacle.

Take the 2 black wires and attach one to the #1 outlet on the temperature controller, and the other to the gold screw on the duplex receptacle.

Take the last black wire and attach it to the #7 outlet on the temperature controller.

Take the black wire from the receptacle, and attach the other end to the #8 outlet. You can also attach the temperature probe to the #3 & #4 outlets.

Then, feed the the replacement power cord through the utility box hole with the cable connector. First connect the green grounding cable to the green screw on the receptacle. Connect all the white wires together with a marrette, then connect the black wire from the power cord to the free end of the black wire from the #1 spot on the temperature controller with another marrette like this:

Tuck the wires back into the box and put the faceplate back on. Screw it into the main box and don’t forget to tighten the cable connector where the wires come in so they don’t pull out unexpectedly.

And there you have it!

All you need to do is set your fridge/freezer to it’s coldest setting, plug it into the receptacle on your new temperature controller box, then plug the temperature controller box into a wall outlet.  Place the sensor probe inside the fridge or freezer. I taped mine to the side of a glass jar filled with water, that way the temperature won’t vary as much as the air, and will give you a more accurate reading. Set your parameters and desired temperature setting using the instructions that came with the temperature controller. My unit only displays in Celsius, so I drew up a handy chart to convert to Fahrenheit: Celcius to Fahrenheit Chart


23 Responses to How to build your own Temperature Controller Box…

  1. Did the controller ship with or without the probe?

  2. That’s identical to the one I built.. works great!.

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  4. Is that temperature controller CSA or UL approved? CE certified?
    If not it might not even be legal to use, not to mention that it might even be unsafe.

    I’m concerned that the internal relays are not up to the task of frequent switching something as large as a refrigerator or freezer. For the sake of safety, especially since the temperature controller comes from China and the spec sheet shows no certifications, you really ought to use an outboard relay capable of switching at least 20 amps, and plug the whole thing into a ground-fault-interruptor receptacle.

    • Hi Henry, thanks for stopping by.
      I’ll have to check on the cert. status. My guess is that it’s not rated,(being from China) but I’ll let you know.
      I did have a concern for the relays as well since the unit is only rated for 10 Amps. I imagine a chest freezer might draw around 12A at start up? I was looking for a 15A model but couldn’t find any. If you were to add a relay to remedy this, where in the circuit would you put it? I do understand a relay’s intended function, but I’m not too familiar with how to wire them. It’s working just fine so far, but a GFCI would probably be a good idea, always smart to have that added protection… thanks for touching upon all this!
      Cheers, Jeff

  5. The inrush current of a fridge or freezer might hit 40 amps for a split second. With repeated on-off cycles you can fry the contacts of the internal relay.

    Email me and I’ll send you a diagram you can post.

  6. avatar Brian Mitchell

    Hi Jeff,

    I just received a couple of the STC 1000 controllers and plan to use one to control a fairly small chest freezer.

    I measured the current and found that the freezer runs at under 3 amps, but at start up, draws 13 amps. The start up draw could in fact be higher, because of course it is a short spike and the meter can only respond so fast.

    I am debating whether to install a secondary relay with higher contact rathing than the 10amp rating of the STC-1000 unit.

    I recall someone suggested that. Did you modify yours by adding a relay?

    If not, is it still performing well without, and roughly how long have you been using it now?

    Thanks for the great info on your website !

    Brian (“Wingeezer” on the forums!

    • Hey Brian!
      Thanks for stopping by! Glad you’re enjoying the site…
      Good timing actually. I just received my relay and socket in the mail yesterday from Digikey. Have yet to install it though. So far, the temp controller is still working fine. Have had it going for a couple months now and maintains a perfect temperature. I’ve set it to hold within 1 degree C, and it’s been great. I’ll send you a diagram for adding the relay into the circuit. I still have to figure out 1 other thing, but I’ll post up some pics of it when I get it finished. If you’re eager to build yours, you could always go ahead with it as is, and update it later, it’ll work fine…
      I’ll be in touch,
      Cheers! Jeff

  7. Jeff,

    What did you use for the external relay? Can you show me a pic or wiring diagram of what you did? I have mine installed and I know my freezer pulls 12A for 1 second at startup before dropping back down to 4.6A at run. Let me know. Thanks!

  8. Just built one of these for myself works great! Thanks for the design.

    • Hi Chris,
      No problem! I’m glad it’s working well for you!
      I just actually made a second one with an internal relay in it which will possibly help prolong the life of the contacts. The original one is working just fine, but thought I’d try it on the second one. I’ll be putting up a post about it in a week or two in case you’re interested…


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  10. What do you use as a heating element in your set up?

    • Hey Brian,
      I don’t use anything for heating. My situation really only calls for keeping things cooler.
      I have heard about people using a low watt light bulb and computer fan to move air around, although I would be very weary of having light bombard your fermenters if they are glass…

  11. I’m no electrictrician so my question may be stupid. Would it be a problem if I used 12 gauge wire instead of 14?

    • Hey Joe,
      Using a heavier gauge wire (smaller #) is always ok, but the opposite not and is dangerous as the wires cannot handle the same load and so could potentially start a fire.
      But to answer your specific question, yes, 12 gauge would be fine instead of 14 gauge…

  12. Hi Jeff. I was reading your post and I was wondering if you ever got around to adding that relay system? I’ve been trying to find diagrams for guidance, but so far i have found very limited explanations.

    • Hi Louis, I did install a relay in my second controller, but haven’t found the time to write a post about it yet. I’ve been MIA with blog posts lately, may apologies!
      It took some experimenting, but I figured it out. I’ll see if I can open it up and map out for you what I did. Do you have the same parts that I mentioned? If not, it may be a slightly different setup.
      I also just revised my thought on using a GFCI in the temp. controller box.I found that it tripped the circuit quite often, leaving things to warm up until I noticed it had tripped. Instead, just plug the unit into a wall outlet that has a GFCI and you’re all set.

      • I have all the same parts except for the relay and the relay socket. is online the only way to order the relay and the socket or do you think i could find those parts in a hardware store/computer store? Also, thanks for the tip about the GFCI.

        • I imagine you could find them at an electronics parts store, but the terminals in which you hook it up may vary. I’m not too versed in these kinds of things really, and like you, found it hard to get any specific diagrams that would fit the bill for this project. Mind you, if you found them somewhere, you could always ask at the store to see if they can suggest how to hook it up. I just got mine online seeing as that was the parts one of my readers suggested…

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