Question Chassis fans, PWM or DC mode ?


Apr 7, 2020
I have 3 BeQuiet Pure Wings 2 120mm PWM used as chassis fans. What difference does it make if i put it in PWM vs. DC mode ?
i7 9700K
Asus Z390-P
Will there be a difference in RPM ?
The main difference is PWM allows operating fans at a much lower RPM than voltage control does. That's because the "bursts" are always full 12 V which can kick the fan to start rotating. The duration of the "kick" just gets shorter (percent of time) in duration to lower the RPM.

DC control just lowers the voltage which doesn't kick it into starting when it gets below about 5V or so. That can damage the fan if left not rotating with 4 or 5 V on it for extended periods so many fan controllers won't give it less than 6 or 7 Volts minimum.

It's less a big deal these days with the ultra-quiet fans made by BeQuiet, Noctua, Arctic and others as the operating RPM at even 9 or 10 volts is whisper quiet.
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What rpm should I set as minimum to maintain good temperature and airflow ?
All systems are different...different fans and cases with different fan locations and as well different ambient temperatures in your room. You have to experiment a little with it, or just pick a speed that's quiet but on the edge of being annoying. If it's still too hot then you may need to go looking for different fans, or examine your fan layout in the case.
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