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

gnydick

I have these cui devices fans, https://www.cuidevices.com/product/thermal-management/dc-fans/axial-fans/cfm-4010c-250-195-20.

When they're not spinning, they whine and measure 3987v across the VIN+/-.

As soon as it starts to run, the whine disappears and the voltage reads 24v.

What the heck? This is making me worry about all sorts of other things this could cause.

Any help?

dc42

@gnydick Are you trying to drive it using PWM? If so then I think you should have selected the -22 version instead of the -20 version, and connected it to the Duet as a 4-wire fan.

elmoret

What device do you have that is capable of measuring four thousand volts?

(There isn't 4kv on those pins, I can promise you that)

mendenmh

@gnydick Is it possible your meter had autoranged to a millivolt range, and you were reading 3987 mV, or about 4 volts, due to leakage currents?

gnydick

@mendenmh I was hoping that, but couldn't see any icon on the screen.

gnydick

@dc42 I was hoping to reserve the 4 wire for the print cooling fan, although 8 haven't been able to find a 5015 24v blower that is 4 wire.

Is this fan not usable? It's seems to work great, speed control is very good.

Is there something wrong with this or is there a better way to configure/connect this fan?

3DPMicro

4kv probably would have jumped a noticable spark to your meter lead and dc42 would have been awarded inventor of the first ever flux capacitor. Think jigawatts
https://youtu.be/VcZe8_RZO8c

gnydick

gnydick

dc42

@gnydick if it's working well, don't worry about it.

It appears that something is confusing your multimeter. What does the H symbol on the multimeter mean?

mendenmh

@gnydick yeek! There is something funny with your meter.

I agree, it shows an mV label when on that range, but I have no idea what it is doing. Have you tried putting it on an appropriate manual range and seeing if it still does this?

I do have one idea. Is the "H" at the top 'Hold" mode. I have seen meters sometimes in hold that hold the number, but not the range info. Could it have captured that number in the mV range, and then switched to a volts range while still holding the display?

gnydick

@dc42 yes, H is for hold. Why is it receiving current when it's off?

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.