Arduino based Brewpi running the latest arduino firmware.
Chest freezer with enough room for two 5 gallon buckets, total of 10 gallons fermenting.
Heat wraps on both buckets.
Temp probe in a thermowell of one of the buckets.
Chamber probe just dangling in the free air of the freezer.
Room probe. Ambient of about 68F
The BrewPi Arduino code wasn’t built to heat the beer directly. It manages the beer temp by managing the fridge temp. If your heaters heat the beer directly, it cannot manage the fridge temperature properly.
You can see that your fridge setting is responding faster than your actual fridge temperature because of this. You might get better results if you decrease Kp.
If you need better control with your setup, you’ll have to modify the Arduino code yourself, or get the BrewPi Spark.
A light bulb will emit a lot of light, which might skunk the beer. In addition I would recommend a heat source with a lower surface temperature. A light bulb will reach at least 130ºC (approx 270ºF) and radiates a lot of heat so everything close to the bulb will get quite hot.
I also disconnected the heat wraps and went with a 40W bulb (sorry Espen, but I’m in the middle of the fermentation…I’ll look into the tubular heater for the next one). I’m in plastic buckets so I am less concerned with light right now.
I’m still curious about what actually is the trigger to start a heat or cool. I would assume it is a difference from the setpoint and the current slope (trend) of the beer temp. The new settings seem to allow the temp to get to about 0.2F above setpoint before starting the cooling.
Skunked beer is not too bad. I went to a training on beer faults a few months ago. They used a set of small pills that was added to perfectly good if not terribly exiting Carlsberg. The funny part was that adding the “skunk” pill made Carlsberg taste a lot like Corona
So as long as you like Corona, don’t worry
PS! To me it seems you seems to be nice and close to the target temp.