Fan doesn't run at full speed with PWM control

  • I've been using this fan on an E3D Hemera and have been running into serious heat creep issues, which didn't make sense as it's a very powerful fan. I have been running it at full speed (tried S1.0 and S255) on a PWM fan header, however I finally tested it on an always on header and it spun a good bit faster. I tested frequencies between 10 and 1kHz with the same result. I think this may be due to some of the anti-stall circuitry etc in the fan not playing nice with PWM.

    I'd like to retain temperature control for the fan, so does anyone have any advice for getting its full power out of a PWM header? Or is there a way to set a fan header to simple on/off? I could wire up a discrete relay but I'd like to leave that as a last resort.


  • administrators

    M106 S1.0 or S255 should always turn the fan full on, without any PWM.

    Which Duet and firmware version are you using, and which fan output?

    Please post your config.g file.

  • Hi dc42, thank you for the quick response. Further troubleshooting has shown this to be a pebcak error - I had my fan wires mixed up at the board. I guess I'll have to check other possible causes for heat creep.

  • administrators

    @copperbricks, I'm glad you solved it,

    Common causes of heat creep:

    • Incorrectly assembled hot end. There must be a gap of several mm between the heater block and the bottom of the heatsink, bridged only by the smooth part of the heat break.
    • Fan mounted the wrong way round, so that it is sucking air out of the heatsink instead of blowing into it. Normally, the fan label should be towards the heatsink (so it is not visible). DO NOT swap over the fan wires, because brushless DC fan motors are not reversible.
    • Print cooling fan blowing too much on the nozzle and heater block (instead of at the print) and no silicone sock over the heater block.

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