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Building a temperature controller

August 9, 2013
Finished product and a celsius to fahrenheit conversion chart (see link below)

Finished product and a celsius to fahrenheit conversion chart (see link below)

I’ve been a little remiss on posting here.  Busy, job, etc.  While I haven’t been as regular updating here, I’ve done a number of fun brews over the past few weeks including:

  • A slightly tart Honey Saison incorporating lemon zest, Nelson Sauvin hops, white wine oak and brettanomyces
  • A full-bodied, super roasty Porter
  • An IPA highlighting Simcoe and Amarillo hops

Posts will be forthcoming with recipes and notes on each.

In the meantime, I’ve also been busy building out some new capabilities.  One of the things that I’ve really skirted by with over the past year or two is fermentation temperature control.  A week or two ago, I finally did something about it… 


If you are a brewer and you are not aware, the two biggest things you can do to improve the quality and consistency of your beers are: filter your water (nothing crazy, a brita will do) and control your fermentation temperature.  Seriously.  It’s incredibly important.


In the winter, my apartment is great for most Ales.  In the warmer months, I struggle.  I can (and do) brew a lot of Farmhouse Ales.  When I want to brew with English or American Ale yeast, I’ve borrowed time in friends’ fermentation chambers and struggled to keep up with a swamp cooler.  I’ll admit I’ve had a few batches fall short of their potential due to poor control.

I finally decided to bite the bullet and put together a proper fermentation control system.  I found a nice, $80 freezer on Craigslist and quickly transported it home to my basement.  It’ll need a collar (wooden extension to increase the height) to fit two fermenters, but for now I can do one.

With the range of beers I like to tinker with, I need the chamber to be able to hold a variety of temperatures, from about 34 Fahrenheit to 90+.  Keeping that in mind, I needed to build a controller that would enable automatic switching between heating and cooling functions.  In the summer, the freezer compressor will run often.  In the winter, my heat source will kick in to raise temperature from ambients as low as 45F.

I haven’t yet decided on what my heat source will be, but I’m leaning toward using the base of a cheap food dehydrator, which has a little fan to circulate warm air.

So.. I built a controller specific to my needs.  This type of controller seems to be fairly common amongst homebrewers and while there was a lot of information out there, I didn’t feel as though I could find it all in one place.  So.. here’s how I did it, and some of the resources I used to put it together.  Oh, and it cost about $40 total.

Parts needed:
  • STC-1000.  110V version (there is a 220V – that won’t work).  Description should be pretty clear.  Includes temperature probe
  • Project box to hold it all.  I got this 4.7 x 4.7 x 3.5″ one
    • Needs to be at least 3″ deep as the STC-1000 is about 2.5 (and need extra space for wires)
  • Standard household outlet with ground (115v, I believe).
    • Ensure that one side (usually gold) has a tab that can be broken off.  This makes it so that one outlet can be to cool and the other to heat.  See image in [link 2] and/or video in [link 3]
  • Outlet cover
  • 3-prong (grounded) extension cord to cut up.  Probably want at least 10 feet
    • Alternatively, get 2 used PC power cords.  One to cut into smaller wires, the other to be the power source
  • Wire nuts for joining the live contacts
  • Electrical tape
  • Dremel to cut holes
    • Alternatively, a small saw
  • Drill to … drill
  • Misc small screwdrivers
  • Wire cutters/strippers
  • Small pliers

High-Level Instructions:

  • Make sure you have all of the parts and tools needed
  • Cut wire into 2x 6″ (or so) sections, and separate into black, green and white sections
    • Strip all ends to between 1/4 and 1/2 inch
  • Cut holes for controller and outlet
    • I installed the controller on the front of the box and the outlet on the rear-facing side
  • Drill holes on left and right sides for power cord and temperature probe
I drilled a small, clean hole in the right hand side for the temperature probe to exit.

I drilled a small, clean hole in the right hand side for the temperature probe to exit.

  • Wire according to the diagram in [link 1]
    • Wiring should be done by snaking wire through holes.  Otherwise, you could have to take it all apart and do it again
    • Take extra care to ensure the positives and negatives to the outlet are correct.  I almost mixed this up and it probably would have been bad
  • Tip: I tied a knot in the power cord (just before where I split it), so that it can’t be pulled out of the box
  • Mark Heat and Cool outlets accordingly, permanently
Clearly marked outlet on the back of the device

Clearly marked outlet on the back of the device

  • Tuck wires into box, close up and plug in to test
  • I used some velcro to affix my controller to the lid of the freezer
  • Assuming all is well, tape probe (best practice is to insulate it on the outer side as well) to the side of fermenter, set temperature, compressor delay (default is 3 minutes, which should be good) and you’re off to the races



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