I have been considering building a fermentation chamber using a mini-fridge as a cold air source, and was wondering how the Ranco or Johnson controllers work. With the Johnson it appears that you just plug the fridge power cord into the controller unit, and place the probe in your chamber, when the temp drops below your set-point the controller powers the fridge until the temp at the probe reaches the set point, and then it shuts the fridge down. Is this correct? Is this how they all work? It seems to me that powering a fridge on an off often would not be good for the compressor, and being able to modify the internal fridge temp controller (if possible?) to reach my desired set-point would be less harmful to the compressor. I guess this goes back to always being told by old timers that when you lost power, you need to wait 5 minutes or so before turning anything back on that uses a compressor for cooling. Am I wrong and possibly missing something? Are there any controllers availble that actually replace the fridges controller and cycle on and off as the fridge was intended to cycle?
How does a Johnson or Ranco temp controller work?
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pernox
Well-Known Member
I can't speak to Ranco or Johnson controllers, but the cheap digital $30 unit I got from an eBay seller has a setting to delay the compressor for x minutes between cycles. I'm not a refrigeration repairman, so I don't know if it's necessary... But I set mine to four minutes anyway. Helps me sleep a little easier, and the 20g of beer don't seem to mind. 
How would a johnson controller be any different than the thermostat that is factory installed with the fidge? Not sure if there really is a time delay on the factory settings. I know when my kids leave my kitchen refridgerator open it kicks on as soon as the temp starts to drop. My fermentation fridge w/ Johnson controller doesn't go on and off any more often or faster than any other appliance. You can also adjust the amount of 'swing' in temperature difference before the controller kicks on.
The controllers, when used properly, do no harm to the compressor. The digital versions allow you to adjust the set point, differential, ant-short cycle delay(Asd), heating or cooling mode and a few others. So, in theory you could choose setting that would actually be easier on the compressor, not harder. The downside to favoring the compressor too much would be wider temp swings. I use a set point of 40F with a 5 degree differential and the Asd set to the 12 minute max. I have the controller set to turn on at the set point and off at the set point minus the differential. A fan inside the freezer keeps everything inside at a very uniform temperature.
Captain_Bigelow
Well-Known Member
I have a JC on my chest freezer. I think it works pretty good. When the temp increases above the desired temp, it turns the freezer on and lets the temp drop to 4 degrees below desired temp. Then it switches the freezer off.
I have the temp probe in a small bottle of water in the freezer, so I am getting the liquid temp rather than the ambient temp.
I have the temp probe in a small bottle of water in the freezer, so I am getting the liquid temp rather than the ambient temp.
Brewineer
Member
If you are concerned about using too 'dumb' a controller with a small differential, putting the probe in a small (~ a cup to a pint) amount of water will allow longer cycling times so you are not short cycling the compressor.
Also, as Catt22 said, a fan to circulate air is very useful, if not required, to get uniform temperatures and improve the accuracy of the temp probe. (especially if it's reading the air)
When I built my keezer, I built my own temp controller with a DS18B20 temp probe and an AVR microcontroller
I set up my differential points fairly far apart (32 and 40) to get a fairly consistent 37.5-38.5 degrees beer temp, but those points were experimentally determined because I am using the probe to test air temp at the intake to the fan. I seem to have reasonable cycling times, the compressor seems to turn on every ~hour for about ~15 min
My brother, a mechanical engineer, was saying that the compressors are designed to run continuously, and the only concern is to run them for too short a cycle.
Also, as Catt22 said, a fan to circulate air is very useful, if not required, to get uniform temperatures and improve the accuracy of the temp probe. (especially if it's reading the air)
When I built my keezer, I built my own temp controller with a DS18B20 temp probe and an AVR microcontroller
I set up my differential points fairly far apart (32 and 40) to get a fairly consistent 37.5-38.5 degrees beer temp, but those points were experimentally determined because I am using the probe to test air temp at the intake to the fan. I seem to have reasonable cycling times, the compressor seems to turn on every ~hour for about ~15 min
My brother, a mechanical engineer, was saying that the compressors are designed to run continuously, and the only concern is to run them for too short a cycle.
OP
OP
nasmeyer
Well-Known Member
Does your fridge plug directly into your controller, or does the controller replace the original controller in the fridge?I can't speak to Ranco or Johnson controllers, but the cheap digital $30 unit I got from an eBay seller has a setting to delay the compressor for x minutes between cycles. I'm not a refrigeration repairman, so I don't know if it's necessary... But I set mine to four minutes anyway. Helps me sleep a little easier, and the 20g of beer don't seem to mind.
Hang Glider
Beer Drinker
I think very few re-wire their compressors / internal controllers
we all mostly just plug the fridge/freezer into the controller, then let the controller do the work. You will want to set the fridge at it's coldest setting, so it won't turn off on it's own - let the controller do the work.
we all mostly just plug the fridge/freezer into the controller, then let the controller do the work. You will want to set the fridge at it's coldest setting, so it won't turn off on it's own - let the controller do the work.
eanmcnulty
Well-Known Member
JThat sounds really simple. Thanks for explaining that. I thought it was some sort of complicated rewiring. Now I'm even more interested in getting a fridge.
pernox
Well-Known Member
As stated above, I plug my fridge into the box, the box has a probe going into the fridge (drill hole, insert probe, seal with silicone) and I plug the box into the wall. I had to wire mine up to an outlet etc, but there are others that are plug n' play. =)
KiltLifter
Well-Known Member
One of my controllers I had to wire myself (Johnson). My analog controller has a plug that goes into the wall socket, then the fridge plugs into the back of that plug - cleaner looking but it sticks out of the wall further.
The probe in a cup of water works well to eliminate short cycling. Mine is in a White Labs yeast tube - the plastic is a bit of an insulator, but the water volume is small so it works out.
Pernox (trying to figure out the acronym, is it one?), Do you still have the Ebay sellers name who makes the cheap ones?
The probe in a cup of water works well to eliminate short cycling. Mine is in a White Labs yeast tube - the plastic is a bit of an insulator, but the water volume is small so it works out.
Pernox (trying to figure out the acronym, is it one?), Do you still have the Ebay sellers name who makes the cheap ones?
pernox
Well-Known Member
Here's a link to the controller I used.
http://cgi.ebay.com/Mini-Digital-Te...tem&pt=LH_DefaultDomain_0&hash=item3f00a8fd21
I agree with not leaving the probe hanging out in thin air. I stuck mine in a length of plastic tubing and keep it wedged between two kegs.
The nick isn't an acronym - it was a character name I chose for a game on a BBS (remember those??) about fifteen years ago. Been using it ever since.
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