Temperature Controlled Freezer

I was trying to setup fermentation chamber by using 7 cubic feet freezer from Lowes and Ranco temperature controller.
What I'm observing is a huge temp variations. Two days ago I have set controller at 68 degree with differential of 3 degree, which means it turns the freezer on at 71 and turns it off at 68. I have put controller probe into a glass jar full of water standing on the bottom of the freezer. What I'm observing is the fact that temperature can drop as low as 61 degree.
My understanding is that when Ranco detects 68 degree and turns the freezer off than there is enough "latency" in freezer to keep cooling for some time.

Is that normal ? Is this toatl 10 degree variation will be an issue for my fermentation ? And how to remediate it ?

Ditch the water and tape the probe to the side of the fermenter. I have also found mine to be most accurate set at a 5f diff.

But how would that help ?

Ranco controller turns freezer off at 68 degree, but for some reason temperature still going down (maybe freezer walls still "cooling" for awhile).
How will repositioning of the probe help ?

Having the probe in the water causes too much lag time and the result will be large temperature swings. It's also not good to have the probe too close to the floor or walls of the freezer. The best solution I have found is to enclose the probe with a short piece of foam pipe insulation. The inside diameter of the foam tube is much larger than the probe and allows the cool air to circulate freely, but prevents the probe from contacting the walls, kegs or anything else. I monitor the fermenter temp with a separate wireless digital indoor/outdoor thermometer. I simply place the transmitter on top of the fermenter or in the case of a carboy, I usually slip it between the handle and the glass. During active fermentation, I usually set the temperature about 5 degrees below what the monitoring thermometer reads. I then observe the fermentation activity and if too vigorous I turn it down even more. Once the fermentation slows, I raise the temp gradually but typically never exceed 64 deg or so. A few days before racking I let it warm up to 70 F to allow the yeast to finish up anything they can grab. This method has worked very well for me.

Wow, lots of useful information ! Thank you Catt22.

I had the same problem--I had my probe in a SS tube, which in turn was placed in a beer bottle filled with water. It took the freezer too long to cool that water down to the temp before the cooling shut off, meaning that the air temp in the rest of the freezer was often MUCH lower. I took the probe out of the water (but still kept it in the SS tube), and presto--the temps are much more stable now. I also "measure" the temp in there with an indoor/outdoor wireless thermometer...

The wireless thermometers are really tits. Cheap too, if you shop around. I think I only paid $9.99 for the ones I have and they are remarkably accurate. I check them with my higher quality traceable digital and they are within a fraction of a degree. All four of them!

spbrewer said:

But how would that help ?

Ranco controller turns freezer off at 68 degree, but for some reason temperature still going down (maybe freezer walls still "cooling" for awhile).
How will repositioning of the probe help ?

Click to expand...

You coulda just took my word for it.