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Old 06-02-2011, 01:43 PM   #1
BugAC
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Default Johnson Digital Temperature Controller

I have mine setup with my frigidaire freezer (14 cu ft).

I'm having trouble with my temp settings, and i can't tell what the problem is.

I have my SP (setpoint) temperature at 65 degrees, and my Diff (differential) set at 3. The rest of the settings are at the default setting.

My sensor is wrapped in a cold pack i got with a shipment, which is set in a cup.
The sensor is pretty accurate, because i have a secondary thermometer in there to get a more accurate reading.

My problem is. My freezer kicked on when i was in the shower. And when i came back down, the temperature was at 58 degrees. Is my differential set too high? Is the freezer just working hard to get the cold pack down 3 degrees and won't shut off until the cold pack gets that temp? I'm thinking this might be the problem and that i should set my differential at 1.

Any thoughts?

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Old 06-02-2011, 01:51 PM   #2
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Yeah I would lower the differential, becasue even after the freezer shuts off, it still gets a couple degrees colder. I would also turn the auto short cycle up all the way to 12 so you don't wear out the compressor with the lower differential. It will only need to come on about once every hour anyway, unless your opening it a lot.
Also, a thermowell in the stopper of the carboy works best, because your taking the tempature of the beer itself.

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Old 06-02-2011, 02:05 PM   #3
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You have to keep in mind that your probe and your thermometer are measuring 2 different readings. The thermo is measuring the ambient air temp. Your probe is measuring the cold pack temp which is more resistant to temp change than the air around it. So in essence the freezer will either shut off when the internal thermo of the freezer hits it's shut off temp or the your temp controller will shut it off when the probe reads the shut off temp, whichever comes first. The freezer internal thermo will almost always shut off the compressor before the temp controller does until the mass that the temp controller probe is measuring gets down to the ambient temp of the freezer. Then the controller will take over.

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Old 06-02-2011, 02:18 PM   #4
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Quote:
a thermowell in the stopper of the carboy works best, because your taking the tempature of the beer itself.
what is a thermowell, and how do i go about setting this up?

My plan, when i got home, was to tape the probe to the outside of the carboy with some paper towels as insulation from the ambient temps.
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Old 06-02-2011, 02:25 PM   #5
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This is a thermowell, but a lot of people just fill a glass or bottle with water, set it next to the carboy, and put the probe in it.

Your idea will work ok. The beer temp will probably be a few degrees warmer than the probe is reading.
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Old 06-02-2011, 02:31 PM   #6
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http://www.rebelbrewer.com/shoppingc...hermowell.html
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Old 06-02-2011, 02:40 PM   #7
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So the probe goes in the metal part, and you can still attach an air lock to it, correct?

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Old 06-02-2011, 02:49 PM   #8
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yep...its just a long metal tube. The stopper has 2 holes in it.

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Old 06-02-2011, 03:07 PM   #9
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Quote:
yep...its just a long metal tube. The stopper has 2 holes in it.
Thanks. Just ordered one.
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Old 06-02-2011, 06:22 PM   #10
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Just to let you know, I had a little trouble fitting the Jonson probe into the thermowell at first, but crimping the probe did the trick. IMO the thermowell is the way to go, because unless you have your probe in a jug of water that is 5 gallons (which would take up a ton of room). It is going to cool and heat faster than your beer. You should be happy with your purchase

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