Fan surging

  • Have what might be a firmware issue, though have NOT done any troubleshooting to verify yet. Timing is suspect though. On my 4th print since updating to 1.19 on a DuetWifi. Never noticed the issue prior. Looking to see if this is isloated and what steps folks would like me to do to locate the issue. Will start on my own troubleshooting after my print finishes here in a couple hours.

    Issue: Fan is surging to XX% then dropping to 0%. I say XX% because it is tied to the percentage I issue via gcode, so if I say %100 then the fan fires up appears to hit the target PWM and then drops to 0, rinse and repeat.

    If I set the fan T %100, it appears to be fine, but it might also be that the off time is so short and speed so high that inertia prevents the fan from dropping in RPM enough to notice. The overall cycle time appears to be the same regardless.

    It feels like the fan is stuck in a continual blip cycle, as if it were using the target speed / pwm target as the blip target over and over and over again.

    I'm in the middle of a print now, so don't want to reset, though it would be a good test of the resume feature… 😉


  • Update: Send M106 to reset the PWM frequency cleared the surging.

    config.g - surging during normal print
    M106 P0 F200

    via gcode console - surging stopped and fan operated as expected
    M106 P0 F300

    via gcode console - set Freq back to 200 to see if that's the issue, result: no change in fan speed nor surging, as expected
    M106 P0 F200

  • administrators

    Some fans don't work well with PWM, but reducing PWM frequency to 100Hz sometimes helps.

  • I have some tiny 12v blowers that I use through a 24V to 12V converter. I don;'t know if it's the fans or the converter that don't work with "normal" PWM frequencies but they work fine by dropping the frequency right down to 10 Hz. Been running them like this for about a year.

  • Seems to be happening everytime now. If I issue a M106 P0 F200, which the config.g starts with, everything clears up. Checked my starting gcode in the slicer, nothing has changed there.

    I believe I found a permanent fix / workaround. I thought this was already set… Added a blip to the fan via M106 B
    config.g now has:
    M106 P0 F200 B.1

    FWIW - Didn't have an issue pre-1.19, not saying it's 1.19 nor aliens, but it's aliens. 😉

    This matter is closed for me with the fix above. Thanks all!

  • Ugh, spoke too soon evidently. What I thought was a fix or work around turned out to be false. The issue persists. Will do more troubleshooting tomorrow.


Looks like your connection to Duet3D was lost, please wait while we try to reconnect.