Support for 3 pin fans?

[jrytio]

I love this board, building a replacement for my AC Infinity dumb controller and I have 2 3pin fans at the top of the rack that will be a nightmare to replace. Normally 3 pin on 4 pin will work fine with just on/off, but with the 3.3 board I'm using, they're just always on when I plug them in. On/off does nothing and RPMs report properly, even when off.

Is there a software change I can make that would let these 3 pin fans work, or is this a hardware limitation?

[Pel1can111]

I’m no expert but I doubt it. 3 pin fans work by changing the voltage applied to the fan where 4 pin fans are supplied a constant voltage and change their speed via a PWM signal on the 4th wire. This would need to be designed at a hardware level to work I would imagine.

[zeroflow]

Hi @jrytio

@Pel1can111 is correct. The hardware only supports 4-pin PWM fans for control. 3-pin fans will run at 100% and the tach signal will work fine, but on/off control isn't possible — that would require additional high-power switching circuitry per channel, which the board doesn't have.

I know swapping out rack fans can be a pain, but in my experience it's usually less bad than expected once you get in there. Decent 4-pin replacements (Noctua, Arctic) are around €10-15 and well worth it for the control you get. Personally, I prefer the Arctic P12 Max which allow for true 0-rpm mode and can still push quite some air on 100%.