Motherboard making up fan RPMs?

JosephKnowsNot · April 1

I was checking in the BIOS(UEFI, I know) recently and noticed the fan RPM readouts, moving slightly up and down (PWM headers). This makes sense with the 4 pin PWM CPU cooler fan. This does not make sense to be displaying slightly different RPM readings for the System fan, considering there isn't one. There is a system fan header. It has nothing plugged in.

It is a proprietary motherboard (HP Lubin). Could it be a representation of the estimated fan speed as per the PWM signal being produced by the motherboard? I can't figure out what else it could be except that, otherwise the numbers wouldn't move slightly up and down as I'm watching.

The CPU cooler fan does speed up under increased load, so PWM is working (at least somewhat).

I've found references to no fan speed, and absurdly high fan speed if the fan is slow, but not made-up fan speeds. Especially not for empty fan headers.

I'd modify the fan speed settings to see what happens, but that is not available on this motherboard.

Has anyone else seen this happen?

Levent · April 1

Way back in the day, I remember seeing prebuilts with two pin fans. Meaning they were only getting power and ground from motherboard. Fan curve and rpms don’t matter if 99% of the users won’t be touching it and company is better off with extra $1 per motherboard, I guess.

I’m gonna go ahead and say, same principle probably still applies to HP.

JosephKnowsNot · April 1

21 minutes ago, Levent said:

prebuilts with two pin fans

They did make quite a few, shall we say, interesting choices, but...

I've taken the fan out and put it back in already, it really is a 4 pin PWM fan. I also temp switched it to another fan, which worked. It clearly varies speed, and if I put a 3 pin fan in, that will run at 100%, so it must be really doing PWM control.

Edited April 1 by JosephKnowsNot
trying to make my reply sound more personable