Question for users of a digital temp controller - Home Brew Forums
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Old 08-01-2008, 10:14 PM   #1
damrass
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Jun 2008
Conway, AR, USA
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So after fermenting a British Bitter at 76 degrees during these scorching summer days in Arkansas, and having the A/C go out after priming the same batch, I decided to get one of these:



My question is basically: how do I use it?? The instructions are kind of cryptic. For example, the Set Point is the temperature at which you want the thing to turn on your fridge. But what does the Differential, the Anti-short Cycle Delay, and the Temperature Offset do?

I've set the Set Point to 55 degrees F, and I've noticed that it kicks on when it gets to 56 degrees F. The problem is it keeps cooling and the temperature sometimes gets to 49 degrees F.

I want to have this figured out by tomorrow. I'm brewing a Nut Brown Ale, and I'd like to let it ferment at around 65 degrees (as measured by the wort, not ambient). Any suggestions on how I should configure this doo-hicky?

I'm a computer programmer for a living, so it makes this post that much more humiliating.
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Old 08-02-2008, 02:24 AM   #2
ExpertBrewers
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Jul 2008
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Hi,

I am not entirely familiar with the Johnson controller but:

Differential -or- Temperature Offset(not sure which one) will control how much fluctuation there is in the temperature, so say you set 55 with a differential/offset of 2 your cooling will kick on at 57 and off at 53

For the Anti-short cycle delay, I would assume this is why the colling keeps going. I have a feeling this keeps the compressor from going on and off repeatedly or on and off in a set period of time.

 
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Old 08-02-2008, 05:26 AM   #3
DutchK9
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May 2008
Springfield, Illinois
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Quote:
Originally Posted by ExpertBrewers View Post
Hi,

I am not entirely familiar with the Johnson controller but:

Differential -or- Temperature Offset(not sure which one) will control how much fluctuation there is in the temperature, so say you set 55 with a differential/offset of 2 your cooling will kick on at 57 and off at 53

For the Anti-short cycle delay, I would assume this is why the colling keeps going. I have a feeling this keeps the compressor from going on and off repeatedly or on and off in a set period of time.
If it didn't have a couple degree offset then your compressor would burn up trying to keep the freezer at the same temperature. With several degrees of play, the compressor won't kick on as much which minimizes damage.

 
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Old 08-02-2008, 05:41 AM   #4
Bytor1100
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Mar 2008
Utah
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You basically set the SP to the temp. you are shooting for, and it will keep it within that range. It will have a certain set degrees of deviance, like said above, this will prevent your compressor from killing itself. When I have mine outside, even a 4 degree swing will turn it on just opening it on hot days.
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Old 08-04-2008, 10:03 PM   #5
damrass
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Jun 2008
Conway, AR, USA
Posts: 118

I basically ended up just playing with it a bit, I still don't know exactly how or why it works but it seems to be keeping the beer at a constant 64 degrees. And man the yeast seem to LOVE it. Woke up this morning with a nice 3-inch healthy krausen less than 24 hours after pitching.

I'm never looking back to the days of hot summer ferments again! I just wish I had a bigger fridge or freezer.
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Old 08-04-2008, 10:20 PM   #6
Eskimo Spy
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Jul 2008
Fort Worth, TX
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Man, thanks for posting this, I was looking at the exact same controller, and had the exact same questions!

 
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Old 08-05-2008, 01:16 AM   #7
stuartm
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Jul 2008
San Jose, CA
Posts: 50

Quote:
Originally Posted by DutchK9 View Post
If it didn't have a couple degree offset then your compressor would burn up trying to keep the freezer at the same temperature. With several degrees of play, the compressor won't kick on as much which minimizes damage.
I just got the Ranco digital today. What's a good setting for the differential to minimize compressor damage while not having the temp swing too much for the beer?

 
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Old 08-05-2008, 07:47 AM   #8
brewjunky
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May 2008
Winnipeg
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I have mine set to 4

 
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Old 08-05-2008, 03:14 PM   #9
keithd
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Feb 2008
Yokota AB, Japan
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I thought differential was the +- from the set temperature, and the offset was how different from actual the controller registered, meaning if it's really 75, and the controller showed 73, the offset was 2.
-keith

 
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Old 08-05-2008, 03:22 PM   #10
GilaMinumBeer
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I have the Ranco and it does not have a temperature offset feature. I assume this may be a calibration setting but could be wrong. For example, if compared to a calibrated lab thermometer the controller reads a difference of 2 degree's then this would allow you to "offset" from the reading to get a more accurate controll. Of course this is speculation on my part.

What has already been said about the differential and setpoint is correct however, you may want to try an experiment with a calibrated themometer.

It's a well known fact that the wort temp can rise up to 10*F during fermentation due to exothermic heat generated by the yeast. I suggest you try to measure that actual temperature of fermentation and utilize a setpoint around that.

For example, I generally set my controller 5 to 8 degree's lower than my desired ferm temp to compensate for the generated heat.

Some brewers simply tape the probe to the side of the fermenter with success and others buy a fermentation thermowell (available from B3).

 
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