Help, whine and 4000v measured on 3pin fan when idle

dc42

@gnydick if the fan is turned complete off, it should only be receiving a few microamps of leakage current.

gnydick

@dc42 i guess that's enough to make it whine?

mendenmh

It would be interesting to put a small load (10k resistor, e.g.) across the fan, and re-measure that voltage. Maybe the board has a leaky FET.

Also, it is possible that the fan draws very little current at low voltage. That may be low enough that nothing is biased on until the voltage is much higher. In that case, you may just be charging some tiny input capacitance, and a small current might create a significant voltage. The load resistor would tell more about this.

gnydick

@dc42 just nudging here. Is there anything I can do to stop this? With 4 tools, it's a cacophony of whining

They're on toolboards.

dc42

@gnydick when exactly do they whine? Is it when they are turned on at a PWM that is too low to make them turn?

gnydick

@dc42 when they aren't powered at all.

T3P3Tony

@gnydick do they whine with the tacho output not connected?

dc42

@gnydick said in Help, whine and 4000v measured on 3pin fan when idle:

@dc42 when they aren't powered at all.

Try disconnecting the tacho wire as @T3P3Tony suggests. If that resolves the issue, then connecting a small signal diode in series with the tacho wire should fix it. Note, when using a 3-wire fan the tacho will only read correctly when the fan is run at full PWM.

gnydick

@dc42 Is that a given with 3 wire fans or a duet quirk?

dc42

@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.

gnydick

@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.