First Lager - Few Temperature Control Questions

I was recently able to get a nice deal on a chest freezer that is perfect size for a carboy/bucket and still has a good amount of space for some bottles or other things. Right away I snagged a Johnson temperature controller off Amazon - http://www.amazon.com/gp/product/B00368D6JA/?tag=skimlinks_replacement-20 - and was getting ready to do my lager brewing tomorrow.

I hooked up the controller just to see how it functioned, got the freezer going, adjusted setpoint to 50F with a 2F differential and watched what happened... well the temp controller showed 48F, shut off, then to my surprise the temp kept dipping... all the way down to 39F. I let the system run for a few hours, but it still seems to overshoot the differential temperature after the controller shuts off - usually down to 41-42F.

Is this common? If so, what are the general rules to compensate and make sure the wort itself maintains the desired average temperature?


Second topic is where to put the temperature probe. I've been reading a lot about taping it to the side of the carboy or bucket itself with some insulation. My concern with this is the following - if you have it reading the wort temperature as described and lets say the wort is hits 51F, the controller will kick on and begin cooling.

Considering the insulation and the probe reading the wort temperature, the controller won't kick off until the wort itself reaches 48F, correct? Seeing as the freezer air temperature will be cooled well below this temperature, won't the wort continue cooling, potentially far below your desired temperature range?

From what I've noticed with my new (1948 GE fridge) ferm chamber is that the air temp fluctuates by about 10*f non-stop. The carboy temp (probe taped to glass carboy with bubble wrap for insulation) varies by less than 2*F.
There should be a setting on your temp controller to adjust the difference in temp which basically controls the tolerance +/- of your set temp.
Read through the directions I'm sure it's in there.

Edit: just reread your post. Yeah. It's because you don't have it taped to the carboy.

Snisup, thanks for the response. I have already found and adjusted the differential temperature you mention and have it set at 2F. The problem seems to be that the freezer refrigerant continues to cool the chamber after the temp controller has shut the compressor off. So the system shuts off once the temperature reaches 48F, but then continues cooling to approximately 41F. Then it will slowly heat back up to 50F, the controller will kick on, cool to 48F, turn off, and the chamber will again cool back all the way down to 40-42F.

Well found some answers after more searching.

http://hbd.org/discus/messages/34426/36272.html

http://www.homebrewersassociation.org/forum/index.php?topic=13984.0

Not much discussion on this topic as far as I can find, so I guess it hasn't really been much of an issue for most.

I think that once you get the temp probe reading the carboy temp instead of the air temp that you will be fine. Even if the chamber air temp drops down to 40 it would take a long time at that temp to effect your carboy temp.

Snisup said:

I think that once you get the temp probe reading the carboy temp instead of the air temp that you will be fine. Even if the chamber air temp drops down to 40 it would take a long time at that temp to effect your carboy temp.

Click to expand...

+1. When you think about it, the air temp inside the freezer/fridge isn't the important reading. It's the temp of the fermenting beer (which can be the same or maybe +8F higher) that matters.

The thermal mass of all that liquid will help stabilize your readings. I have my STC-1000 tolerance set at +/-0.6*C and haven't had a problem with the fridge I use now nor the freezer I used to use (which is now my lagering/cold crash chamber). When you get your bucket/carboy in there and tape the sensor to its side then insulate it from the air (I use bubble wrap), all should be well.

BTW - welcome to the "temp control club". You're gonna love it.