Fermentation Fridge - compressor cycle question

[brad2157]

I recently picked up an older refrigerator through craigslist and spent some time fixing it like I wanted.....it was white originally, so I painted it black all over, painted the front with chalkboard paint, replaced the inside door panels with dry erase whiteboard, built a shelf in the bottom to hold the weight of full fermenters, added a fan to circulate the air in the bottom section, added a light for the heat circuit and added/installed a stc-1000 in the front corner of the door.

I programmed the stc-1000 to test it out initially with the compressor setting at 4 minutes (meaning it has to be at least 4 minutes between the compressor turning back on again after it hits the target temp and cuts off. I programmed the temp variance at 4 degrees. My question is...how do I know if the compressor will not burn up having to turn off and on so many times to hold a steady temp that I set to ferment at? I have no idea how often a normal refrigerator turns on and off and what would be considered normal. I have it in my garage, which gets really hot during the day, which is why I need the fermentation fridge to begin with.

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[Orthobrewsky]

It would be best to wrap the probe in insulation to prevent rapid temp changes. I would also set the compressor delay to 10 minutes, just in case.

 

[Orthobrewsky]

By "insulation" I just mean something to keep it from direct contact with the air. You could wrap a paper towel around it and zip that up in a little Ziplock bag. Some use bubble wrap.

 

[mongoose33]

If you do insulate the probe against the fermentor I think a 4 degree variance is way too much. Do you really want your fermenting beer to rise and fall 4 degrees over and over? I'd be thinking of a degree or maybe two, but not four.

As Ortho above notes, you should insulate your probe against the fermentor so it reads the temp of the fermenting beer, not the air temperature. Here's a pic showing how I have the probe insulated and held against the side of my fermentor. I cut a very shallow groove in the foam so as to encapsulate the probe, and the foam surrounds the probe as it holds it against the fermentor.

You won't see the compressor clicking on and off--if you're measuring the temp of the fermenting beer, it won't gain or lose heat all that fast, so your compressor won't be cycling all that often.

 

[brad2157]

Thanks for the advice, I really appreciate it. I realize more now that my tests as-is were not the best with the temp probe hanging down beside the circulation fan. I will get a piece of foam and a strap and set my temp probe up like yours to get a more accurate and stable temp.

 

[jivy26]

If you do insulate the probe against the fermentor I think a 4 degree variance is way too much. Do you really want your fermenting beer to rise and fall 4 degrees over and over? I'd be thinking of a degree or maybe two, but not four.

As Ortho above notes, you should insulate your probe against the fermentor so it reads the temp of the fermenting beer, not the air temperature. Here's a pic showing how I have the probe insulated and held against the side of my fermentor. I cut a very shallow groove in the foam so as to encapsulate the probe, and the foam surrounds the probe as it holds it against the fermentor.

You won't see the compressor clicking on and off--if you're measuring the temp of the fermenting beer, it won't gain or lose heat all that fast, so your compressor won't be cycling all that often.

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This makes complete sense and I am an idiot for not doing this lol! So take some foam, cut a small divot for the probe and use a bungee to secure against the carboy.

My only other question is if you are fermenting two in your freezer, would it be best to put the probe against the smaller carboy?

Also I am ignorant to refrigeration and compressors, so setting the value to 10 mins does what exactly? Thanks tons for the info and time!

 

[brad2157]

This makes complete sense and I am an idiot for not doing this lol! So take some foam, cut a small divot for the probe and use a bungee to secure against the carboy.

My only other question is if you are fermenting two in your freezer, would it be best to put the probe against the smaller carboy?

Also I am ignorant to refrigeration and compressors, so setting the value to 10 mins does what exactly? Thanks tons for the info and time!

The 10 minute setting referred to, means that even if the temp is out of range by the variance value (4 degrees in my original example / post), it will still wait 10 minutes before the compressor will kick on and start cooling again. Otherwise if you had the fermentation refrigerator set at say 67 degrees for example with a variance of 2 degrees. If it is not holding the temp well, the compressor may constantly cycle on-off-on-off to try to maintain the 67-69 degrees (the 2 degree variance setting). This would burn out the compressor doing so. That setting makes sure there is at least a 10 minute rest period for the compressor from turning back on again. Hopefully I have explained it well enough.

 

[jivy26]

Oh perfect sense! Thanks!

 

[mongoose33]

My only other question is if you are fermenting two in your freezer, would it be best to put the probe against the smaller carboy?

Yes, that's what I would do. If you insulated the larger one (meaning more liquid in it), then to take it down a degree might take the smaller one down 2 or 3 or 4 degrees by the time it got the larger one cooled.