Effects of a temp controller?

I made a kegerator out of the Danby DAR125SLDD (the 4.4cf unit from Walmart). I put my outdoor wireless "weather station" that has a temp data recorder on it inside the fridge. The first week or so while it was empty it was pretty stable in the 37 to 40 range, but once I put the first keg in it and I am seeing a big swing, say 32 to 42. Right now when the compressor kicks on it it stays on for maybe 2-3 minutes or so and usually kicks on every 30 to 45 minutes.

I was thinking about getting a temp controller but then got to thinking, if my fridge works this way and has this type of temp loss in a 30-45 minute period, it seems as if with a controller the fridge would kick on every 5 minutes for 30 seconds or so and just in turn make the whole unit die faster. Is this in fact the effect a temp controller has on a fridge?

No, a temperature controller doesn't have to work that way. You can set a delay to make sure the compressor isn't kicking on every couple minutes.

An important issue is where you're actually measuring the temperature. The air temperature inside a kegerator is going to fluctuate, but I bet you'll find that the beer temperature is much more stable. If you tape a probe to the outside of one of your kegs and put some insulation over it that would be a useful experiment.

With the full kegs in the fridge, the air temperature is going to definitely oscillate more during each cycle, but the beer temperature is not. Air has much less thermal mass than water (beer) so the beer will change temperature much more slowly than the air. This is desirable from a compressor cycling point of view, deeper and more infrequent cycles will extend the life of the compressor. You'd probably see the same thing if the fridge was full of food as intended by the manufacturer; this is why it's usually not recommended to leave a fridge completely empty, since it'll make the compressor cycle more.

An advantage of the temp controller is that it allows you to put the probe wherever you want.

I run a digital Johnson controller, set for a +/-1* temp swing with no time delay - but all of that's adjustable if you have a decent digital temperature controller. I keep the probe inside a thermowell that sits inside the middle of the carboy, so it's measuring the core liquid temperature. I'm using my controller to turn on / off some heat tape wrapped around the carboy, so there's no concern with cycling on or off too quickly (thus my small range of temperatures and no time delay) but I had once upon a time done the same thing with the carboy in a cooler. As mentioned before - the temperature swing and cycle intervals are much better when you're measuring the liquid temperature and controlling the compressor that way. I'd wager that you'd actually see better results by using an after-market temperature controller set to a reasonable range, measuring the liquid temperature directly vs. your keezer's stock temp probe measuring air temperature.

-Kevin

BadNewsBrewery said:

[...]I'd wager that you'd actually see better results by using an after-market temperature controller set to a reasonable range, measuring the liquid temperature directly vs. your keezer's stock temp probe measuring air temperature.

Click to expand...

That'd be easy money - if you could only find some takers...

Cheers!