24 replies to this topic

[djinkc]

Mine are fairly accurate. I think they all had an adjustable swing and 3df was the lowest swing setting. I have one running the kegerator, which hasn't been adjusted in over a year. And a couple that run tandem fermentation chambers - with the bulb in thermowells. They are a workhorse and will last a long time if treated well. It just takes a while to fine tune where they need to be set at to achieve the temps you want.

[AGrandDesign]

For those of you that use Johnson analog units, how closely does the set temp on the unit match the actual temp in your fridge/freezer, allowing for time to stabilize? I am wondering because it seems I have to set mine quite a bit lower than the actual temp I want to achieve. I am waiting for a scientific thermometer accurate within 1/2 degree that is being shipped to me to calibrate, so it could be that the Johnson controller is more accurate than the brewing thermometers I have in the fridge sitting in a glass of water. Anyways, any feedback from others would be great.

I've used my Johnson analog (bought used off ebay, so no telling what it went thru before me) thru one just one fermentation so far and, like you, I had to set quite a bit lower (I think by 7-8 degrees) than target temp. Once I worked out where it needed to be it did great...at least according to my digital probe thermometer I used to cross-check with. The bulb on mine is a bit dinged and the instructions that came with it said this may knock calibration off. Hope that helps.

[Jimmy James]

Thanks DJ and AGD. It seems like what I am seeing is typical with my unit. It holds a temp fine, but there is some difference between the set temp and actual temp achieved. I appreciate the responses.

[djinkc]

Thanks DJ and AGD. It seems like what I am seeing is typical with my unit. It holds a temp fine, but there is some difference between the set temp and actual temp achieved. I appreciate the responses.

The problem with these, if you really consider it a problem, is the swing. When I put the bulb in a thermowell for a 10+ gal batch that is a huge thermal mass. And especially with bigger beers that can create a lot of heat so, I would rather error on the lower side for temps. I usually set them a little low when I anticipate an active primary fermentation and the bump them up a little once thats done.I know I could have another smaller liquid/gel container with the bulb in there instead of the fermenting wort - but this seems to work OK here so I haven't changed. My concern is letting a primary fermentation get too hot - those first couple days can really screw things up IMO.For the kegerator, who cares about the differential.....One thing is the circuit board will never fry on these.

[3rd party JKor]

my johnson is digital.0. 1.

Edited by JKoravos, 08 May 2009 - 05:52 PM.