PID tuning for none fridge setup


My current setup is without a fridge as I don’t currently have room for one. My setup is:

  • Fermentation vessel containing beer (currently just water for testing) and a temp sensor in a thermowell.
  • This is placed in another container that is filled with water, two fish tank heaters, and the “fridge temp” sensor (a bath if you like).
  • The whole lot is living in the cold garage, my pseudo fridge.

Attached is a screen shot of the data logged so far. I know it’s probably within tolerance but the temp is oscillating a little around the set point, if I wanted to stop it what do I adjust to stop it ?


If you do not have a cooler, uninstall the device from device manager (set function to none).
It will then not go into the cooling state. There is a minimum time to wait when switching between heating and cooling.

Also post the screenshot with the all lines enabled. (beer setting is disabled).

Cooler disabled, missing trace enabled, screenshot and zoomed screenshot added.

Thanks !

OK, telling BrewPi I had no cooler help settle things out as can be seen on the left of the attached screengrab. However on playing around a bit more and increasing the temperature I now have an offset of around 1degree. Any suggestions ?

What is the absolute maximum temperature? And what is PID max? And what is Kp, Ki, Kd?

Check your advanced settings and the control panel tab.

The “Absolute max temp” was set to 30 but I noticed it clipping to I upped it to 35 just before the last temp change, it didn’t seem to alter the problem.
All other values are default:
PID: Max 10
Kp: 5
Ki: 0.25
Kd -1.5

Image with the rest of the config values is attached.

Okay, you are not clipping to PID max or absolute max now.

But for some reason, even though the fridge temperature is above the beer temp all the time, the beer temp does not rise.
Now there are 3 options:

  • Increase Kp, Ki and Kd for a more aggressive control algorithm and more difference between beer and fridge temp.
  • Increase the max temp error for the integrator (0.5C default, I would increase it in your case). The integrator action will get you out of a steady state error like this.
  • Think about your sensor placement: my guess is that the beer is cold on one side and hotter on the other side due to the heater placement. Your sensor is on the hot side. Your cold outside temperature makes me suspect this.

Ok, sounds like plenty to try. I have two heaters in the bath, (I couldn’t bare the asymmetry). Fridge sensor is close to the fermentation vessel. Pics of the setup attached, see what you think.

I forgot that you had a water bath setup.

Strange that the beer doesn’t take over the water bath temperature, I would have expected that. I’d say the setup looks pretty much ideal. Maybe the thermowell or top of the bucket is affected by the cold air? But I suppose during active fermentation the beer is moving around quite a bit. How long is the thermowell? Does it go deep into the beer?

You could also try putting a box over the bucket to get still air around it.

The tip of the thermowell is about mid height in the beer, around 10-11 inches down from the lid. Probably about where the water bath ends. I figured it was going to give me an average beer temperature in the mid way position. It is thermally isolated from the retaining nut in the lid to.

Combining the lid suggestion with the PID advice certainly gives me enough to be going on with. Thanks for all the help, outstanding !