Help Fine Tuning


Just hacked my small fridge for some more fermentation capacity, finally hooked up the brewpi spark. Looking for help fine tuning settings, right now the temp swing from constant is about 1.5-2 deg F.

Current Settings (I believe these are the factory defaults)
Beer-to-Fridge proportional gain (Kp) = 2
Beer-to-Fridge integral time constant (Ti) = 7200
Beer-to-Fridge derivative time constant (Td) = 1200
Maximum difference between fridge and beer set point (= output of PID) = 18
Beer-to-Fridge Input filter delay time = 18
Beer-to-Fridge Derivative filter delay time = 159
Cooler proportional gain (Kp) = 10
Cooler integral time constant (Ti) = 1800
Cooler derivative time constant (Td) = 200
Cooler PWM period (seconds) = 1200
Cooler minimum OFF time = 180
Cooler minimum ON time = 120
Cooler Input filter delay time = 18 seconds
Cooler Derivative filter delay time = 159 seconds
Heater 1 proportional gain (Kp) = 10
Heater 1 integral time constant (Ti) = 600
Heater 1 derivative time constant (Td) = 60
Heater 1 PWM period (seconds) = 4
Heater 1 Input filter delay time = 18 seconds
Heater 1 Derivative filter delay time = 159 seconds
Dead time when switching between actuators = 1800

Also, how to I calibrate temp sensors, mine are off by about 1.3 F. I have a thermopen so I trust the readings.


Please make a new screenshot that is more zoomed in.

This one help?

I don’t think it is possible to do much better.

The compressor is already starting up very often. The temperature just rises very quickly after you stop cooling. The only way to make it smoother would be to run the compressor even more often, which I would not recommend.
Once you have some thermal load in the fridge, it will probably be smoother. You can also decide to put your fridge sensor in a glass of water. (okay on the BrewPi Spark, not on Arduino).

What about using the ice pack gel in a old white labs yeast vial? I’m assuming that would be better than water.