Need Help to get stable Temperatur

Hello Community

I have been trying to cool a litle Fridge with a certain temperature (20°) for a day with many different settings. The result so far is fluctuating between 19.8° + 21° which does not satisfy me.
My setting is as follows:
A cool box (small refrigerator with Peltier element)
Spark 3
SSR Relay
Peltier element
Raspberry 4 with Brewblox
18b20 Temperature Sensors
Can someone explain to me with which settings I can create a stable temperature with my equipment

Thank you I am grateful for any help

Before continuing: you are sure you want to optimize your system around steady fridge temperature, not beer temperature?

This indeed looks to be a small freezer, that rapidly warms up between compressor cycles. While beer temp can typically be tuned to <0.1degC error, your fridge itself will always be more volatile.

Hi Bob

Thank you for your Answer!

No, i’am not sure! Just playing around with possible settings, to be honest i’am lost in the possibilitys …
I just want to have a stable Temp. in this Chamber whatever setting its needed :slight_smile: With a cheap china Temp Controller i get a variation of ±0.2°. But i need the historical graph thats why i choose Brewpi.

I’am not sure if i better should use the old Version of BrewPi?

I think a 1 degree fluctuation in air temperature is totally fine.

If you want it tighter, you can decrease the pwm period and minimum on time.

But first look at/share the PID internal graph zoomed in on a few cycles. We can’t say much from just this graph.

However, it looks like your PWM value is fairly stable, so it will depend entirely on how quickly you want it to cycle.

A good start would be to remove the min on/off constraints from your cool actuator, and significantly shorten the PWM period. Those settings are required for a fridge compressor, and your peltier doesn’t need them.

You should start seeing a smoother temperature curve, where the cooler constantly adjusts instead of cycling.

Thank you both for your help!

I have adjusted the settings and wait a day for the temperature to adjust.
I will get back to you after that.

Thank you!

Just a thought. As your system is so small and can cycle quickly (peltier over compressor) you could try removing the integral and differential components of the PID controller (set to 0) and then just adjust the proportional (k) until you get a stable temp. If it takes ages to reach it without Overshooting then you need the I and D.image

Actually, that’s not correct.

Yes, you would have to tune Kp until you get only a small bit of overshoot.
But with some derivative gain, you could run a higher Kp and get a faster system without overshoot.

The integrator will never reduce overshoot, only increase it. But its purpose is to adjust for constant temperature losses. Without the integrator, you would reach a stable situation slightly under the setpoint.

Sorry! I think I garbled my answer!

Finally I installed the “old” image and now the cooling works stable. With the brewblox firmware I had reboots of the Spark 3 controller from time to time.
It still takes quite a long time until the temperature is stable but that is surely still to be improved. I think I have to adjust the settings in the Maintenance Panel in Control Algorithm, but I don’t know which ones yet…

I work with this Settings:

Result is this

I did a reboot and made a calibration Offset thats why there is an outbreake

I really don’t recommend switching back to BrewPi.
We will not support it any longer. Please let us help you get a stable system with BrewBlox instead soon.

Hi Elco

As soon as I can buy another SD card I can try to install Brewblox again.

But I also found the installation of brewpi easier than with Brewblox. Since I don’t brew beer I can’t do much with the quick modes.
In brewpi I can simply define a sensor and a switch actuator (cooling or heating) and I can start …
I do not know how to do the same in brewblox.

As I said as soon as I can buy a new SD card (lockdown) I will come back for another try.

Thank you for the Support!

Hi Elco

I have received the new ordered BrewPi Spark 3 and would now like to try to control my incubator with the Brewblox software.
Here again as a reminder my setting:
I have a cabinet with a heater that I have used with Brewpi as an incubator for several years. It is controlled by the Brewpi software and it works very well so far. I can reach an accuracy of max. ± 0.1° which I consider very good.
you wrote:
Please let us help you get a stable system with BrewBlox instead soon.

How can I now do the same with Brewblox? What exactly do I have to do to achieve this goal?

Does the incubator use a “beer” temp sensor, or is it purely based on air temp?
If it is the latter: today’s release includes a wizard for that. It will be live in <1 hour.

Hi Bob

Thank you for the answer.
I do not understand your question about the beer temp sensor, what do you mean?

My construction of the incubator and Spark 3 looks like this.

A DS18B20 is connected to the Spark 3 and a heating element in the cabinet is switched by an SSR relay.
The information that the setup of Brewblox will take <1hour is of course very nice but does not help me in detail. :wink: Can you give a little more details please?

The <1h referred to when the update would be released.
It is released now.

After installation, go to wizardry -> quick start, and run the “Fridge without beer sensor” wizard.

Let it run for an hour, and then post a screenshot of the graph. We’ll have a look then whether temp control can be better.

I did the installation this morning, how to update?

Run brewblox-ctl update

i did the update but now i get the message


Could you please run brewblox-ctl log?