Always on Fan "Zooms" Periodically
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This happens with my Nova hot end, about every minute: The fan is reasonably quiet, then all of a sudden, I hear it revving up (the pitch of the sound goes up) over about 5 seconds or so, then it gradually slows down again over about 20 seconds.
I don't know why it does this, but it's really annoying to hear over and over. Is the Duet somehow detecting that the fan is slowing down gradually and then increasing power to it to try to bring it up to speed or something?
It's not a defective fan, because I've replaced the fan and it still does this.
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@DonStauffer What do you mean by "always on" how are you powering the fan, what board is it connected to and what pins/port is it using? What is the fan voltage?
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@gloomyandy 24V fan. Duet 2 WiFi has 2 different kinds of fan connectors. Some (3 I think) are PWM fans whose speed can be controlled by GCode, intended for part cooling fans. Two are "Always on" connectors intended for hot end heat sink fans that stay on at a constant speed (in theory) to keep the "cold end" cool.
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Can you measure your VIN output from the PSU with a multimeter while it's doing this? Do you have a DC bed heater as well? How powerful are the heaters in the hotend? Are they perhaps causing the voltage to droop from your PSU?
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@Phaedrux I can take measurements. The hot end heaters are 100W but I haven't had them on in days, so that's not causing it. The bed heater is AC and also hasn't been on in a while. Certainly neither has been on today, and that video was recorded a couple hours ago.
The timing of the "revving" is pretty reliably slightly less than 60 seconds. So something is "cycling". I've been working on NeoPixel macros for quite a while so the printer has been on but idle. But this isn't a new phenomenon. It's been since I installed the Nova as far as I can remember, many months ago. It's just started to drive me batty with no other printer sounds to cover it up.
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@DonStauffer Assuming you have the VFAN selector set to 24V those always on pins should be connected directly (via a fuse) to the 24V psu. If your voltage measurements don't show anything odd, you could try connecting them directly to the psu 24V supply and see they still change sound, that would eliminate the Duet2 as a possible cause.
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@gloomyandy Sounds like a good troubleshooting procedure. Thanks!
