Keezer – Digital Thermostat

A chest freezer has many advantages over a standard refrigerator.  One of them being the thermal efficiencies gained by avoiding a front-opening door that spills all the cold air out every time it’s opened.  Indeed I have recently tested my keezer and a digital thermometer placed inside, halfway down, doesn’t even move by 0.1C when the lid is opened (carefully) for a short period of time.

Unlike a refrigerator, however, a freezer must be run with some form of thermostat.  People routinely store normal bottled beer in their home fridges but uncontrolled a freezer will (obviously) freeze them.  I don’t see this as an encumbrance at all – I don’t like my beer at household fridge (food preserving) temperature anyway, so I would have to run a thermostat regardless.

I already run a digital thermostat on my fermenting fridge.  And another one on my HLT.  These are both STC-1000 thermostats, which provide both heating and cooling circuits.  The thermostat that I have ordered for the keezer only has one switched output – it’s a Willhi WH7016C (again bought on ebay and cheap: $15).  I don’t like the interface on this unit as much as the STC, but that might just be a familiarity issue at this point in time.

Just like my previous thermostats I placed this one in a black project box and wired it up by cutting an extension cord in half to provide the power connections.  Some people like to install these units into their keezers but I didn’t for a number of reasons: I think that a visible display ruins the look of a full-wood keezer; I don’t intend to change the temperature very much so what’s the point?; this keezer is going to live in a domestic space (do I really want to be watching a movie with the room lit up by the keezer display?); if I installed it inside the keezer it would be subject to temperature fluctuation and presumably condensation.

Just like the HLT temperature controller I wired this one up with an RCA plug for the NTC temperature probe.  This meant that I could use a bulkhead fitting RCA socket on the back of the keezer, making it easy to seal any holes that pass through the wall of the keezer collar.  It also means that the thermostat box is completely removable, which is clearly useful if the keezer ever needs to be moved.

The probe itself sits inside the keezer.  I’ve just left it dangling about halfway down so that it’s measuring the temperature of the mass of air in the center of the keezer.  I figure this is probably a sensible location for it and will prevent it from fluctuating if the lid is ever opened.

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