DIY temperature controller for freezer/keezer

Whether you’re just starting out with kegging or you’ve been doing it a while and are looking for more capacity by getting a chest freezer, this DIY project to build a temperature controller (using an STC-1000) for a chest freezer is perfect for you. For about $40 you can build this controller to instantly convert your freezer into a kegerator (“keezer”) without modifying the freezer itself!

Keezers are great because they have the capacity for multiple corny kegs and when opened, the cool air stays inside. Personally I wanted the simple, fast, and inexpensive project with the option to pimp out later. Currently my freezer has the CO2 and kegs inside, hooked up to cobra picnic taps rather than going elaborate with tap lines and all that.

Without some kind of temperature controller, a chest freezer will get too cold for your beer. This DIY temp controller solves that problem and cuts the cost in half compared to buying one new. The nice thing too is that this is a dual stage temperature controller, so it can control both a heating & cooling element, so you can also use it for a fermentation chamber if you want! Are you ready to take the leap?

This project has been done by many people. However, there are some things that aren’t completely clear in the assembly, so here’s everything step-by-step starting with what you need:

110V AC version of the “Mini Digital Temperature Controller” STC-1000 (for an aquarium) Amazon: $16.95 & Amazon Prime shipping

eBay: $15-20 shipped. Most of these are shipped from Hong Kong, so be prepared for a long wait & check estimated delivery date before you choose this option. If my eBay link doesn’t work, search “digital temperature controller 110v”, and SEE BELOW:

Check before you buy:

Product specs: Make sure to get the 110V AC version. I f it doesn’t say, it’s probably the 110V standard version, but if it says 220V AC or 12V DC you’re getting the wrong one and it won’t work properly.

f it doesn’t say, it’s probably the 110V standard version, but if it says 220V AC or 12V DC you’re getting the wrong one and it won’t work properly. Shipping cost and estimated delivery – most of these come from Hong Kong with cheap/free shipping, but some can take a while to arrive.

Warning: If your chest freezer’s load rating is higher than 10A at 250V it might be too much for the STC-1000 to handle and could damage the unit or blow a fuse in it! 15-25ft extension cord – $7 – (OR get a computer power cord for free) – need one that has a ground wire (3 prongs) Thanks to a poster on reddit.com who had this great idea: If you work for a medium/large company, go to the IT department and ask them for a computer power cable – they’ll likely be happy to get rid of one because it saves them paying for recycling. (6) 8 inch length pieces of wire, cut from the extension cord (see below) 7″x5″x3″ project box (from Radio Shack) – $7 2-socket electrical outlet & wall plate – $2 Screw-on wire joining cap – $0.50 Wire cutter/stripper Dremel cutting tool or small saw to cut holes in the project box

First, trace out the outline of the temp controller & electrical outlet on the project box. Then use whatever tool you have to cut out holes in the box – you’ll also need two small round holes, one for the entering extension cord, and one for the exiting temperature sensor from the digital controller. Next, prep the extension cord by cutting off the female end and exposing 24 inches or so of the 3 wires, green, white, and black. Cut all three off in two 8 inch sections, leaving 8 inches coming out of the cord, and giving you six pieces of 8 inch wires. Use a wire stripper to strip the ends off both ends of your 6 wires & the ends from the extension cord. Next, take a look at your 2-socket outlet – on one side you’ll see two silver screws going into a silver plate. On the other side are gold screws and a gold plate. There are tabs on either side of the outlet connecting each of the two plates, silver & gold.

With needle nose pliers, break off the tab on the gold side. This will allow the temperature controller to send power to one outlet at a time – one for cold, and one for heat. You will likely only need the cold side, which is where you will plug in your freezer, unless you want to use this device as a fermentation chamber controller with heat & cooling elements. Now you’re ready to wire this all together!

The STC-1000 temperature controller comes with a wiring diagram telling you what each of the 8 terminals on the back represents. Use this diagram along with my description & pictures to do the STC-1ooo wiring. Please note that I am not an electrician nor do I have formal training in electrical work. You’re doing this at your own risk, just like me – I take no liability for anything that may happen to you or your property.

STC-1000 wiring for the keezer temp controller – gold screws closest to temp controller box

First I’ll explain the wires coming out of the extension cord. The green wire is your ground wire. Attach this to the (usually) green screw on the corner on the back of your outlet. The white cord is the power return (completes the circuit). Attach this on the silver side as shown in the picture (which is the same side as the outlet that will be the “cooling” outlet. The black (power) wire you will leave for now, you are going to be joining this with three other wires at the end.

Now for the 6 wires that go into the back of the digital controller unit. In the picture above, you see eight slots for wires to go into, divided into four pairs of two. I used all black and white wires, but there is no rhyme or reason for which I used for which spot. From left to right in the image, they are: Power, Temp Sensor, Heating, Cooling. Take 3 of your free wires, and put one of them in the first of each of the paired slots for Power, Heating, & Cooling. After these 3 wires are screwed into the temp controller, join/twist the free ends with the black wire from the extension cord with the screw-on wire joining cap. Only 3 wires to go! Put the remaining three wires in the second of each of the paired slots for Power, Heating, & Cooling. The one from the power slot goes to the silver side of the outlet, on the side of the for the “heating” outlet. The one from the heating slot goes on the gold side, also on the side of the “heating” outlet. The one from cooling goes to the other outlet on the gold side. Finally, hook up both ends of the temperature sensor into it’s slots on the unit, and run the sensor end out of the box. Tuck all your wires into the box, screw the box shut, and you’re done! Now you have a fully functioning dual stage temperature controller to use for whatever meets your needs. Remember – check the load rating of your chest freezer ahead of time – a savvy reader pointed out to me that some older units could push beyond the rating of the STC-1000 (10A @ 250V) and damage it or blow a fuse when trying to kick in the compressor. However, this build has now been working solidly for my chest freezer that fits 3 corny kegs for more than two years — also, for those interested, see below about what you can do to prevent this problem by adding an external relay.

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ADDENDUM for those interested in adding an external relay: I have received a few comments regarding whether the way I have the temperature controller wired could damage it due to it directly mounted to the current of the freezer (see comments section). A helpful reader Gary was kind enough to put together a diagram (below), and had the following to say in an email which I will quote since he knows way more than me on the subject! This is the type of relay he recommended: http://www.hottubworks.com/part-2-G4B-item-spa-electrical-relays.php

“The 3/16″ pinouts(stakons) are the 120 vac magnetic coil and the 1/4″ stakons are for the dry contacts, the contacts that will bear the load of the fridge or freezer’s compressor and fan. I will find a minute to send you a simple circuit drawing. Clearly, one has to choose a relay that not only has the similar specs, but also will fit into the control box. You will see that the drawing emulates exactly what you have already done with the addition of the extra relay. Remember that the current (amps) while the compressor runs can generate heat sufficient to destroy that nice little controller of yours. If you add the relay as drawn, any heat build-up will be handled there instead of at the controller.”