Temp swings in an atypical fermenter setup

Hi everyone… I’m brand new here and I’m in the process of fermenting my first beer with my BrewPi setup (RPi 3, arduino uno, plastic bucket fermenter with thermowell).

I still have a lot to learn about the advanced setup, which I haven’t touched yet… But I’m seeing my beer temp having some larger temp fluctuations than before, and it seems like BrewPi is overcompensating and creating some wild swings… Can anyone shed light on potential reasons?

Some background:

  • my ferm chamber is a Mother of Fermentation Chillers, I used the plans from wort-o-matic… Insulation is good but not great, I will be making upgrades to that after this brew

  • cooling happens by blowing a computer fan across ice and into the chamber. It works, did some tests on water and was able to control temp well (but not as quickly as I’m assuming a fridge or freezer would).

  • heat comes from a lamp inside used to melt those smelly wax things.

Is fermentation picking up and that’s why the beer temp is fluctuating like that? Do I need to adjust some settings in BrewPi (they’re all at default now)?

Any help or insight would be welcome!


Do you have an Arduino of BrewPi Spark?

  • You have a lot of delay between changing the fridge temp and the beer actually responding to it.
  • Your fridge temp seems to follow the setpoint nicely.

I think you should decrease your beer-to-fridge gain (Kp), so corrections are more gentile. You also want to make the integrator slower (increase Ti) and maybe use a bit more derivative (increase Td).

Hi Elco

Thanks for your reply, I’m using an arduino, not a spark.

My Kp was set at 5 so I adjusted down as you recommended to 4. Is that enough or should I make small adjustments and just see what the effect is?

As for adjusting Ti and Td I don’t see a spot for that in the advanced settings… Like I mentioned before I’m completely green with this stuff but really enjoying it.

My beer is slow to respond to the “fridge” because it’s not an actual fridge. This is what I’m using more or less:


I would go lower than 4, try 2.5.

On the Arduino, you’ll have Ki and Kd. Reduce Ki and Increase Kd.

Thanks for your help on this… Does this seem more in line?

Also, since “heat” is a lamp and “cool” is a computer fan with ice, I don’t think I need to worry about minimum cycle times or delays between on and off… Do you agree?

yep, but most of these times are not configurable in the Arduino version.

Just noticed my Control Algorithm tab doesn’t display correctly? Anyone know why?
I had some pretty wild swings in temp.

beergutbrew, the control algorithm tab displaying json like that is a BrewPi Spark thing, but the settings you show are Arduino settings. You should use the updater to switch to the legacy version if you are using Arduino.

We are not maintaining the Arduino version anymore and with the legacy version, you get an older version of the web interface that is still compatible.