I am doing a lot of small 1 gallon batches, so i decided to build a tiny temperature controlled fermentation chamber for them.  With only a small budget, using a compressor fridge was out of the question.

There are a lot of second hand thermoelectric cooler boxes on the internet sold for very cheap. I bought 2 of them and added a arduino brewpi controller.


I mostly use 5l mason jars for trial fermentation and they fit perfectly. You could also use big PET plastic bottles or stainless steel growler.

The chambers work great and the temperature is very stable. They only cost me around 50$ each, diy brewpi included. They are not perfect, because of some drawbacks of the peltier coolers. Crash cooling is not possible because the peltier coolers can only reach about 15C below ambient. You could still put the fermenters in the fridge if crash cooling is needed. Because of the fan, they are a little bit noisy.

You can see the spikes in the ambient temperature when the box is cooling. This is because it gives of heat.

Choose a coolbox with interior fan for the project, they work much better.

The first step was to clean the Thermoelectric Cooler and remove the top cover with the Peltier element behind. Sometimes they have their own temperature control circuit board, you can remove that. There should be just 2 wires going to the peltier element and 2 wires for the fan.


I had to add a small copper plate heat spreader to the DC-DC converter. Because of the conversion from 12V it got very hot.


To switch the polarity of the peltier element, you can either use a H-Bridge from eBay or make one yourself with cheap eBay relays.


Homemade H-Bridge.


I added a third relay to control the fan. There are 3 temperature sensors connected to the 1wire bus.


To put everything back together and make the brewpi fit, i had to remove some of the insulation.

The finished setup works very well. Now i can even make Lagers in the heat of summer.


View of the interior. I added a thermowell to the mason jar. You can also stick it to the side of the fermenter and insulate it with bubble wrap.

A old computer power supply is used to power the box. You could also buy a nice LED power supply from ebay. Get one with at least 8A output.


If you build one yourself, please let me know and post something in the comments.


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