fermentation freezer help

[DirtyHaus]

I just got my hands on a 5 cubic ft chest freezer and a johnson controls single stage temp controller. I plan on fermenting my first lager using this rig in a few days and thought i'd figure out how to get the temp controller to work before brew day.

So i read the instructions and figured out how to set the controller to 45 degrees and set the differential to 4 degrees. The problem I'm facing is that even though the controller is set to 45 degrees, the temp in the freezer is dropping way lower than the set point (28 degrees last time i checked). I've tested and made sure the freezer is shutting off at the right temp but it just seems to keep dropping after it cools past the set point. I have the probe in an empty glass carboy thats sitting on the bottom of the freezer but not sure if that would matter. I'm located in florida and it hasn't been colder than 48 degrees in my garage where the freezer is. Thanks everyone for all your help!

 

[moparx12]

hmm. sounds like a problem with calibration. i am not an expert on those so i will let someone else chime in on this.

 

[Brulosopher]

You will hear tons of ideas as to where the probe should be placed. Many, including Jamil Z., advocate for taping it to the side of your carboy/bucket. I haven't have the best luck with this method and have chosen to tape it to the wall of my freezer (with some cardboard between the freezer and probe)... this allows me better control over ambient temp. So...

At least one potential explanation for why your temp is getting cooler than set has to do with the fact your probe is in a carboy, which takes longer to cool than the ambient air. Try taking the probe out of the carboy.

Good luck!

 

[ResumeMan]

Try putting it in a full carboy (just with water). I bet that will help; the thermal mass of the water will minimize the temperature swings.

What is probably happening is that the freezer is making the walls really cold, which starts to cool the air (much more slowly). When the probe in the middle of the freezer hits 45, it turns off the freezer, but the walls have already been cooled way down and they tend to stay that way, so the air keeps getting cooler.

A nice 5+ gallon hunk of water in there should smooth things out for you nicely.

 

[helibrewer]

With a probe in liquid, that freezer is going to run until the liquid gets to the set temp, the ambient air in the freezer will be MUCH colder than the set temp. Once the liquid mass is sufficiently cooled your ambient temps won't swing down so low.

 

[biestie]

Try putting it in a full carboy (just with water). I bet that will help; the thermal mass of the water will minimize the temperature swings.

What is probably happening is that the freezer is making the walls really cold, which starts to cool the air (much more slowly). When the probe in the middle of the freezer hits 45, it turns off the freezer, but the walls have already been cooled way down and they tend to stay that way, so the air keeps getting cooler.

A nice 5+ gallon hunk of water in there should smooth things out for you nicely.

This, although I wouldn't put the probe in the carboy... just tape it to the side with some sort of basic insulation.

 

[Bob1976]

If you put probe in a large container of water or you tape to side of Carboy (jamil way) set the differential to 1. If you leave probe in air 4 degrees is good, but set to 47 so beer sees average of 45.
It works best once beer is at 45. Cool down is tricky. I like to use air probe until at temp then tape to side. If you tape to side of warm beer the freezer will run until it gets to ~0. (it's set point in normal operation ). Not bad if nothing else is in the freezer.
Earlier post is correct about over shoot on cold sides.