Introduction: Peltier Fermentation Chamber for Beer

PLEASE NOTE: This is still a work in progress. My first tests were disappointing and I'll be making improvements in the future.

Most homebrewers know the importance of controlling the fermentation of their beer. I initially used fridges, but fridges only cool the beer down. What if you need a chamber that can both heat and cool?

Enter the peltier! Peltier modules get hot on one side and cold on the other when voltage is applied to them. If you reverse the polarity of the voltage, the hot and cold sides on the peltier are switched. Peltiers are the heart of this project.

The total cost was about R1600, which isn't exactly cheap in my books.

Step 1: What You'll Need


  1. 2x Peltiers. I used 12V, 6A models. They are cheap on ebay.
  2. 4x Heatsinks with fans (I used 100x100mm square computer CPU coolers).
  3. An insulated box big enough for your fermentor.
  4. An STC-1000 (or other) temperature controller.
  5. 4x SPDT Relays that can handle 12+ amps. (I used automotive relays).
  6. Enough female terminal lugs (the yellow ones will work nicely, the blue ones are a bit to small for multiple wires).
  7. 1x 12V 12+ amps power supply.
  8. 1x 12V 1A power supply.
  9. 8x M3 30mm screws with nuts.
  10. 2x electrical screw terminals (sometimes called "chocolate blocks").
  11. 1x 3 point plug.
  12. 3-4m of 3 core electrical wire.


  1. Access to a 3D printer.
  2. Wire stripper.
  3. Crimping tool.
  4. Power tool to cut with (depends on your insulated box).
  5. Drill (depends on your insulated box).
  6. Set of screw drivers.

Step 2: Understanding the Circuit


This circuit diagram is pretty messy. There is a TinyCad and Proteus file if you'd like to work from a computer program. The red wires represent the positive (+) from the small power supply while black represents negative (-). The brown wires represent positive (+) from the larger power supply while blue represents negative (-). The switches represent the relays in the STC which are operated to heat or cool.

Why so many relays?

  • 2 "power" relays: The internal STC relays are only rated to 10A each. We want to switch 12A or more (depending on your Peltier). This could damage the STC's internal relays. For this reason we will let 2 of our bigger relays do the heavy 12A+ switching.
  • 2 "polarity" relays: To automatically reverse the hot and cold sides on the peltiers, we need to reverse the polarity. This is achieved by 2 additional relays (if you had a DPDT relay you'd probably only need 1). The concept for switching the polarity using a relay is similar to this instructable.

Why 2 12V power supplies?

The smaller power supply will be used to power the coils of the relays. When each relay is activated is determined by your STC. The larger 12V supply will power your Peltiers.

Step 3: Set Up Your CPU Coolers

  1. Download and 3D print 2 of each STL file. You can print the components without support and the "legs" facing up.
  2. Apply your thermal past to the CPU coolers (if it doesn't come pre-applied).
  3. Place 1 peltier between 2 heat sinks.
  4. Fit the 3D printed components over the two heat sinks.
  5. Insert a M3 screw into each hole. Then add a nut to the screw.
  6. Tighten the screws and nuts so that the 2 coolers are pulled together. Try to tighten the 4 screws evenly.
  7. Test (optional). At this point it is recommended that you temporarily connect the peltier and to fans to the power supply. See if you can feel the temperature difference between the 2 sides of your newly assembled cooler.

Step 4: Wiring Everything Up

  1. Cut off 1-2m of your 3 core wire.
  2. The left over piece will be what plugs into the wall, so be sure to keep it long enough.
  3. Fit your 3 point plug to the one piece of 3 core wire.
  4. Strip out the individual wires of your other 3 core wire.
  5. Connect the relays as in the previous step. Here you will use some of your stripped out wire and terminal lugs.
  6. Connect the main power to the equipment as in the picture.
    • Use the screw terminals to connect the legs of the power supply to the relevant wires.
  7. Join this circuit to the relay circuit. You'll possibly need to look at both circuits to do this.
  8. Test. If your fans are spinning and nothing is on fire, feel you can feel the temperature difference between the hot and cold side. Try tricking the STC into changing the polarity of the Peltiers and feel if you can notice the difference. The difference isn't big but it is there.
  9. Mark the normally hot and cold sides. We need to make sure that both heat sinks are heating/cooling on the same side when blowing into the chamber.

The pictures show the STC, relays and small power supply in a container which I did not specify under "materials". My plan initially was to build them directly onto the chamber, but I couldn't get the right box for the chamber.

Step 5: Build/Get a Chamber

Here you have some freedom. What we'd like to end up with here is a well insulated chamber that will be big enough to hold your fermentor. Initially I planned to use 80mm thick polystyrene, but ended up stuffing a plastic tote with PET roof insulation.

Step 6: Mount Your Electronics

Now we will mount everything to the chamber. The end result is that the one side of the cooler is blowing air into the chamber, while the other side blows air into the environment.

Step 7: Test

The first tests of the chamber were disappointing. It was tested with 20L of liquid in the fermentor. After running for about 8 hours it only managed to reach 3C below ambient temperature. I'll be making improvements and posting them here in the future.