[Solved] BrewPi losing precise control

I’ve been using my BrewPi for a couple of fermentations now (10 gallon batches) and it’s worked flawlessly. However, this latest fermentation seems to be acting a little odd. I’m no longer seeing as tight of control over the temperatures. Normally I would see sways of .1 degrees F, but now it’s swaying almost a full degree. In the graph you can see that it was holding the temp at 67F solid over several days, but as I ramped up to 70F over 24 hours it started losing control and hasn’t regained since. I’ve done a couple of times before and I’ve never seen this behavior. Any ideas?

My current set-up uses a deep freeze for cooling and a reptile heating lamp (100W) for heating. The fridge probe is hanging in the middle “air” of the freezer, while the the beer sensor is in a thermowell. I also have a fan running 24/7 to move the freezer air around.

Below is a current graph of my fermentation. All of the annotations at the end are me screwing around with the temperature mode.

Any ideas? Should I be adjusting any settings?

I’ve posted something similar in the how’s my graph look thread How does my graph look? but on the opposite end http://oldlarrybrewingco.tk im actually trying to lager at the moment so want to get it down to 1c.

As you can see from my .tk log I’ve run some mine tests and If I very gradually reduce the temp it seems to hold but if I drop it several degrees quickly it seems to struggle to settle down.

For info I restarted the log so this follow on from my post in the graph thread. And my previous brew dropped from 22c to 1c and had no problems at all and nothing in my set up has changed between jan and March

You could try dropping it down to the lowest point 68f (?) and see if that stabalises it and then ramp up from there?

It almost looks like your heater and cooler are swapped. Can you post a new screenshot of the problem part with fridge and beer setting enabled?

I’ve checked that the Cooling/Heating are correct. I wondered about them being swapped as well. Looks like they are correct, as when in cooling mode my freezer comes on and the heater comes on when in heating mode. Here is an updated screenshot.

okay, let’s forget about your heater and cooler setup, because the fridge temp is following the fridge setting very well.
Please try halving Kp and Ki, leave Kd.
You can look at the control tab yourself to view how the fridge setting is calculated. This will give you a better idea of what is wrong. I think because of the fan in your setup, the fridge and beer respond very fast, so you do not need aggressive settings. Kp = 2, Ki = 0.1 and Kd= -1 will probably work well.

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I’ve halved the Kp/Ki settings and adjusted Kd from -1.5 to -1. I’ll monitor things and see how it goes.

@bglass77, just out of curiosity, how did everything shape up after you adjusted your control settings?

Since making the changes, I’ve returned to having solid control again.