Unusual readings from my fermentation setup


I’ve got my fridge setup and it’s been working for some time now but I recently noticed the following

As you can see for the first 3 days of this graph (and the previous brew) it maintained a reasonably stable temp in my beer but starting on the 10th something weird is happening.

As far as I’m aware no one had touched the fridge in a week.

Any clues ?

Thanks in advance


It looks like the same problem as Sudden cooling just out of range of beer settings.

That seems to have been fixed by installing the latest update.

Thanks Bob.

I did think of that and did an upgrade last friday (15th) but it still appears to be happening. I was interstate over the weekend and this is what greeted me this morning.

Can I get any further info to try and look a little deeper ?



It seems like your cooling settings are just much too aggressive.

Can you show the graph of the cool PID?
What is Kp set to?

Can you also make a photo of your setup? Do you have a thermowell?

Here is the Cool PID Graph. Trying to track down Kp.
No thermowell. I’m using a glass Carboy and I haven’t figured out how to use a thermowell without cracking the glass :wink:
The temp probe is in the wort.

Please share the graph with the legend included. But I can already see that it goes to max cooling all the time.

This might be a good options as a thermowell:

Sorry. Included now

Thanks for the Thermowell tip. I’ll grab on now ! :slight_smile:

Ah, do you have a very short Ti? It should be 2h at least, perhaps 4h would be better.

I haven’t set one from memory. How do I set it ?

In the expanded PID settings.

Found it. Thanks bumped to 2h and will keep an eye on it.
Appreciate the rapid responses !

What was it set to?

Ti (time constant of the integrator) is the time it takes for the integral to grow (with the same amount as what the proportional part is).
The purpose of the integrator is to correct long term errors. It should therefore be much slower than normal process response times.

If you set it to 1 minute, it comes down to this (simplified):
Proportional output is set to 10% due to a 0.1 degree error.

The integrator says 'hey, we have been cooling for a minute already and are still not on target! Better bump that to 20%! And it will continue to increase by 10% every minute.

So the beer is given no time to respond to cooling and the integrator ramps up the output to 100% much too fast.

Ti was set to 1m.
Not sure why it was like this. I don’t remember setting it but if I did it was months ago.

Ok now I’ve broken something with the current ferment.
As you can see from the profile it should have bumped the temp up but hasn’t.
Essentially the red line (target temp) has moved but the orange line (actual temp) hasn’t moved.
I’ve had a quick look but can’t figure it out. Any clues would be greatly appreciated.

Isn’t it just following the fridge setting?