Sensible values to use with Fanshim daemon

The support libraries for the Pimoroni fanshim come with a sample daemon process which you can run from systemd and thus automatically control the starting and stopping of your fan to moderate your system’s temperature.

By default, the daemon will start the fan if your system temperature goes above 36 degrees C, and then stop it again if it drops below 34. These setting seem a little silly to me, since the system will go above 36 even at idle, and then will drop by 2 degrees very quickly with the fan running. The result is that on an idle system your fan is continually stopping and starting.

AIUI, the throttling temperature is 80C, meaning we should try to keep well below that, but trying to keep it down to 36C seems excessive.

My objective would be to have the fan off when the system is idle, then cut in if system load causes the temperature to rise. I’ve been experimenting a bit and currently have the trigger threshold set to 55 degrees C, and the hysteresis set to 15C, meaning the fan comes on at 55 and goes off again at 40.

Can anyone with more knowledge of these things advise whether this is a good idea, and if not what would be more sensible settings?


Which model Pi is this? Since I’ve not seen the Pi 4 go below 36 degrees at idle yet! In fact these defaults are probably silly in the opposite direction since my Pi 4 (which has been idle over the weekend on my office desk) is currently at 64C!

Ultimately, though, I don’t know what the best temperatures are, they will vary depending upon your ambient air temperature, load, choice of Pi, etc.

Since you can’t damage your Pi by loading it without cooling (it will just aggressively throttle the CPU) my best advice would be to test some settings and see how you get on.

I’ve recently added CPU load detection into the daemon, too, so it’s capable of kicking in the fan if it thinks your Pi is going to be hot at some point in the futue. I might need to come back to this code, though, since I think it could have better damping on the on/off frequency of the fan and probably make more intelligent decisions about when to enable it.

Which model Pi is this?

Pi 4

Since I’ve not seen the Pi 4 go below 36 degrees at idle yet!

Isn’t that just repeating what I said? Hence why I was talking about improving the settings.

It does go below 36 using the fan, but with the default settings it’s just on-off-on-off.

For information - the settings which I suggested above seem to be working quite well.

Uh yes. Yes it is. I totally misread!

I’ll update the defaults to be a little saner.