Multiple fans 1 pwm 2 on full?



  • So i try´d to figure out a good way to solve this. but im stuck.
    I Have a M106 fan that is pwm controlled and i have 2 bigger 80mm fans on the side with airducts aimed at the nozzleheight to get more cooling. they really dont like pwm and anything under 100% makes them scream digital noise.
    Is there a simple way to make fans "see" that m106 is started and automaticlly turn on 2 fans on full? 🙂


  • Moderator

    Can you put those fans on the always on port or wire them directly to VIN?

    If they are part cooling fans you could try leaving them on a PWM port but experiment with altering the PWM frequency until you find one they don't complain about.

    What Duet? What firmware version? How are they wired now?



  • They are partcooling fans. that help cool bigger parts when i print fast so i have one on each side.
    so i need to be able to shut them off when printing petg because they blow to much and make petg warp.
    i tested changing pwm freq buth its prettty much the same the fans make weird noise no matter what i set.

    Firmware i use is 3.2 b4 and i run duet wifi 1.03 with duex2


  • Moderator

    How bout a physical switch or a relay instead of a PWM port? In other words, use the fan or heater port to switch a mosfet that powers the fans from VIN directly.



  • @Phaedrux well i wanted to have them turn on automaticlly now i have to sitt and babysitt the first 2 layers just to wait untill layer 3 to kick the fans on.
    that´s why i asked if it was possible to detect when the normal partcooling fan kicks on to also kick on the side fans.

    now i have a macro that i start and stop the fans with buth i wanted it to be automaticcly 😛


  • Moderator

    It would be automatic. Your normal part cooling fan commands could enable the mosfet and turn on the fans. If the fans don't like the PWM from the Duet, then they get powered directly by VIN, but still controlled on and off by the Duet.



  • If you use the Blip value, you can probably eliminate the noise (they probably have a high start torque requirement).

    But you can also set minimum PWM duty for any given fan. So M106... ...L 255 . Would set the fan to the kind of on/off mode you want.
    I don't know if you can set that up for multiple output pins that are all the same 'fan' in the RRF logic...


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