Help, whine and 4000v measured on 3pin fan when idle
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@dc42 Is that a given with 3 wire fans or a duet quirk?
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@gnydick it's a given with 3 wire fans that if you PWM them (which they are not designed for, same as with most 2-wire fans), and the PWM is applied by interrupting the negative supply (which is how all 3D printer boards that I know of do it) then the tacho will not read accurately. This doesn't matter if the fan is used only at zero and full speed, which is typical for a hot end heatsink fan.
If you want variable speed and a tacho readout, use a 4-wire fan.
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@dc42, ok, just curious. These are always running at full speed, so it's all good for a 3 wire. They're the cold section fans.