DIY Digital Temperature Controller for Homebrewers

DIY Digital Temperature Controller for Homebrewers

So someone gave you a freezer, and you want to turn it into a kegerator? Or a fermenter?

You have two basic options:

1. buy something
2. build something

The typical "buy" option is a Johnson Controls Digital Thermostat Control Unit . You put the sensor inside the freezer, plug the freezer into the controller, then plug the controller into an outlet. Quick and easy. You can get these from your local brewer supply shop, or online, about $80.

If you want to build something, you have, again, two basic options:

1. replace the temperature controller
2. build a separate device

I've done both. Replacing the temperature controller gives you a sleek look but is more time consuming, and takes marginally more expertise. I had to mess with spidery cobwebs, muck, and dirt. And, I didn't really like the placement of it, for adjustment purposes.

Fermenter with DIY Integrated Temperature Controller

Kegerator with DIY Integrated Temperature Controller

Closeup of Temperature Controller

The separate controller has some advantages:

Front of Controller

• it's easier to build
• You can easily move it from one freezer to another
• You can place it wherever you want, or even move it around
• You can pick it up and bring it up to eye level to set
• You don't have to tear into your freezer

I built this for about $30, but you could do it cheaper if you scavenge some parts.The essential item is the temperature controller for $16. I bought everything from Amazon using Amazon Prime, and got everything in the mail two days later (Try Amazon Prime 30-Day Free Trial ).

Parts List

Docooler® Digital Temperature Controller


computer power socket


Power Outlet


A Project Box


I think you could use a cigar box instead of the project box, and it would look pretty cool. The sockets could be scavenged from whatever you have around. I decided to use a computer cord, but I could have easily taken an old power cord from some other appliance, or buy a power cord rather than a socket.

In addition to the above items, I used some spade-style connectors and wire that I already had. No soldering - everything was done with a crimper.

The same temperature controller seems to be available under a number of different brand names. I've used the docooler brand three times with no trouble. The instructions are not that clear, so I've written up what I think are better instructions.

Instructions

Prepare the box

Cut three holes in your project box to fit the thermostat, the power inlet, and the power outlet. In my case, these were all squarish holes that I cut by drilling pilot holes and using a coping saw. The project case was actually easy to cut with a utility knife, so I trimmed everything nicely with the utility knife. Drill another hole for the thermostat wire.

As you can see, I put the two power sockets on one end, and the controller and thermostat wire on the other end.

Make some wires with leads

In my case, I used the spade connectors. This was extremely neat and clean and easy. Based on the wiring diagram, I needed:

• 2 pieces of wire about 6 inches long with a spade connector on one end, and a stripped portion on the other
• 1 piece of wire about 4 inches long with a space connector on each end (yellow in the pictures - used as a ground wire)
• 2 wiring parts that had two wires coming out of a single spade connector, and stripped wire on the other ends. See the picture below. See how there are two red wires coming out of a single crimped connector?

The spade connectors will attach to the power sockets, and the stripped ends will connect into the controller.

Put it together

Put the controller in the box. There are two sliding pieces that secure the controller into the opening. I took these sliding pieces off, put the controller in the box, then snapped the sliding pieces back on, and snugged them up. These are the orange pieces on the right side of the picture below.

The two power outlets were attached in different ways. The computer power socket (power IN from a wall outlet) used two screws. I used self-tapping metal screws, but some small wood screws would have looked better. 

The regular 110V power socket (power OUT to the freezer) snapped into place. This one was more critical to get the hole size correct, and trim some of the interior ridges for a good fit.

Connect the wires

So this is the part that's a little tougher to see in the pictures. Not difficult, but you have to get it right.

I describe the wiring below, and based on finished picture. In reality, I connected all the pies to the controller first, and replaced the wire guard. Then slide the controller into place and cinched it up with the orange sliding pieces. Then connected up the spade connectors.

In the picture below, the controller is at the top, the IN power connector is on the bottom left, and the OUT power connector is on the bottom right. The guillotine-style connectors on the controller are numbered from right to left, 1 through 6. Six is on the left. One is on the right. This is consistent with the wiring diagram that comes with the controller.

Starting with the IN power connector on the bottom left. The 2-blue-wire connector goes into controller connectors one and three. The 2-red-wire connector goes into controller connector four, and the right side of the OUT power connector. 

The yellow wire is the ground, and goes directly between the ground posts on the IN and OUT power connectors. 

Finally, there is one more wire from the OUT power connector left-post (light blue in the picture above). This goes into the controller connector number two.

Finish it up

Lastly, I gently pushed the wires into the box and screwed the lid onto the project box.

I used an old computer power cord to plug into the IN side, then plugged the freezer into the OUT side, and dropped the thermostat into the freezer.

Some people will wrap the end of the thermostat with a gel-pack or attach it directly to the fermenter or keg. This helps keep the controller from repeatedly turning off and on too quickly.

The instructions are not very good, so I've written up some instructions in another post.

My last enhancement was to put some peel-and-stick magnetic sheet on one side. I can now put the whole box on the top, side, front or back of the freezer and it will stay there! I generally keep it on the side with the digital readout facing me for easy reading and setting changes.

cheers!