Temp controller, measuring temp reliable?

[Incongruent]

I've attached a diagram of my temp controller I just setup for the first time yesterday.

I'm wondering: how well does the heat from the warmers distribute within the liquid of the fermenter ? If I'm measuring the temp of the liquid in the fermenter to control when to turn on / off the warmers... is it possible the temp where the thermal sensor is will be significantly different from the temp of the liquid closest to the warmers? Eg: temp at Center Top of bucket is 15deg, but the warmers have heated the temp near them to 20 or something like that? Or does the heat transfer evenly to the surrounding liquid easily?

Also, what should I set the hysteresis to for best results?


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Old parts laying around: ac/dc transformer. 12V 1.25A.

View attachment 1482555674636.jpg

 

[doug293cz]

During the lag phase, prior to active fermentation start. and after active fermentation has slowed, you may have significant temp gradients within the fermenter. While active fermentation is going on, there is a good deal of internal agitation (die to CO2 evolution) so temp gradients will be much less. The actual magnitude of the gradients will depend on how well the whole system is insulated. The better insulated, the less heat will be lost to the surroundings, the less heat will be required from the heaters for make up, and the lower the internal gradients will be. Tough to say anything more definitive than that from the information you have given.

Brew on

 

[Sadu]

As above, during active fermentation the yeast are having a party and there is so much movement that I don't think there would be much in the way of hotspots. After active fermentation having an exact temperature is less important. Before active fermentation, I try to place the heating device lower on the fermentor and the probe near the top - as the wort heats the heat will rise and maintain somewhat even heat distribution.

 

[Incongruent]

Thanks guys. Its been a while since I had a clear fermenter so I had forgotten about all the bubbling that goes on during fermentation. That should distribute heat well. Both your answers were very well explained and exactly what I needed to know. Thanks!

I'm thirsty for knowledge, so Doug you teased me with the potential for more explanations if you had more information. What information would you want in order to say more? .

 

[doug293cz]

Thanks guys. Its been a while since I had a clear fermenter so I had forgotten about all the bubbling that goes on during fermentation. That should distribute heat well. Both your answers were very well explained and exactly what I needed to know. Thanks!

I'm thirsty for knowledge, so Doug you teased me with the potential for more explanations if you had more information. What information would you want in order to say more? .

With details about insulation "R" values, heater sizes, output & placement, vessel material & thickness, vessel dimensions, liquid volume, thermowell placement, etc., a good thermal modeler could give you some idea of what the thermal gradients might be. But, I am not a good thermal modeler. I worked with several, so know what they can do, and the kinds of data they need to do it.

Brew on