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Author Topic: Temperature controller with only a chest freezer -- problems with overcooling  (Read 806 times)

Offline amanosz

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I'm testing out a new Inkbord 308 temperature controller for the first time with a chest freezer.  I tested it out first by just cooling some wort prior to pitching any yeast, and I am having problems with it overcooling.  Wort started at ~75F, and I set the temp to 54 overnight, but it overcooled to 46.  It took the whole day with the top open to warm back up to 54.  Ambient temperature outside the freezer for the day was 65-70 but will go as low as 50 at night. The controller can control a heater but I don't have one and I'm wondering if I can get away without a heater wrap.

Perhaps in retrospect, this isn't too surprising -- it takes a lot of energy and time to cool the wort, so by the time the wort hits temperature, the temperature difference between the wort and inside the freezer has become quite large and the residual "cold" can further cool the wort. Probe is taped to the side of a plastic carboy, with small towell insulating the probe. 

I recognize that the fermentation itself will generate some heat to counteract some overcooling, but my question is if it's enough to prevent overcooling. Or do I need to spring for a heater wrap?  How can I make it work with just a freezer for cooling?  I've also tried keeping the top propped open, with limited luck (wort at 54, changed set temp to 53, and it overcooled to 51, even during a warm day (~70F).

Offline santoch

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One trick is to tape your probe to the outside of your fermenting vessel, so it is measuring the temp of that instead of the air around it, which varies a lot more.


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Offline amanosz

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Yes that's what I've done. The probe is required to the outside of the carboy, sorry for the confusion

Offline Ortizer

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Yes that's what I've done. The probe is required to the outside of the carboy, sorry for the confusion
Do you have a fan circulating the air?  The temp differential can get decently high between the bottom and top of a chest freezer.  Also, what is the controller programmed to in terms of Max temperature differential?

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Offline Oiscout

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I had same problem till I isolated the temp prove with some tape from ambient air, and set the freezer on the highest setting it can go. (Not coldest). Also you can set a 10 minute delay on the cylcle. That may help you so it doesn't repeatedly cycle on.

As far as temperature tolerance for low/high I found that 3 degrees was sweet spot

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Offline HopDen

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2 things, put your temp probe into a pint mason jar filled with tap water. Use the lid also by putting a hole just big enough for the probe. Secondly, turn the temp control on the chest freezer to the highest setting. It maybe that you have it set too low. This is how I have my chest freezer, storage for kegs only and it works great.

narvin

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The only time I had problems with overcooling was when I had to drop the temp 20+ degrees overnight for the beginning of lager fermentation. In this case, I'll just compensate by setting the target temp above what I actually want by 5-10 degrees.

If your wort is at or near the set point, you shouldn't get more than a degree of overshoot even when using a thermowell. Taping the probe to the side of the carboy yields similar results.  I keep the max differential set to 1 degree since the mass of the beer is enough to prevent excessive cycling of the freezer.

Offline amanosz

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The only time I had problems with overcooling was when I had to drop the temp 20+ degrees overnight for the beginning of lager fermentation. In this case, I'll just compensate by setting the target temp above what I actually want by 5-10 degrees.

If your wort is at or near the set point, you shouldn't get more than a degree of overshoot even when using a thermowell. Taping the probe to the side of the carboy yields similar results.  I keep the max differential set to 1 degree since the mass of the beer is enough to prevent excessive cycling of the freezer.

Cool that's good to know. The first cool down is easy to compensate for!