Beer Temp Variance

Hey folks, anyone able to offer any advice on why the beer temp is swinging - is this to do with minimum heat and cool times? Any chance of tweaking the PID settings which are as follows:
Kp - 5
Ki - 0.25
Kd - 1.5

In the grand scheme of things its not a huge wobble - 19.83 - 18.94 but I’ve seen people with very little movement and hoped I could tweak something. Using a 30w bar heater in a hacked fridge.

I know its probably choosing to cool and heat based on an algorithm, but why, at the highlighted section, would it cool? the temp is dropping and it makes hardly any difference to the beer temp.

Why doesn’t the heater “feather” on and off much more frequently?


At that point, the fridge setting dropped below the fridge temperature and therefore it starts cooling.

Given that your beer temperature responds pretty quickly to the fridge temperature, I would:

  • Reduce Ki to 0.1. With a slower integrator you’ll get less overshoot
  • Reduce Kp to 2.
  • Try with Kd zero. I think the sharp drop is because the delayed derivative. Alternatively, you can also increase the filtering on the derivative.

The whole algorithm will change in the next update, so I would not worry too much about it now.

Many thanks Elco - that seemed to keep things much tighter to the set point. I have now updated to .4 firmware and it’s all over the place again - I am bamboozled by the terms, derivative etc, so I just need numbers/settings etc to change. Many thanks.

Sorry about that. I almost have an update ready that will prevent alternating behavior like that.
Until then, try uninstalling your heater or cooler, whichever you think is not needed at the moment.

Btw, did you tape a sensor to the outside of your beer? Why is it fluctuating so quickly?

Thanks for the swift reply Elco - I’m bottle conditioning and have the beer temp sensor in an open bottle, might that be a contributing factor?

Yes, definitely. I would switch to fridge constant mode with just 1 actuator installed.

I’ve tried to un-install the cooler - I’m assuming I do this by “unassigning” device slot, function etc, then I hit apply and refresh device list, but it still shows. Am I doing something wrong?

Set the function to None and click apply.