Can't turn off PWM FAN1 (0 and 2 OK)



  • Duet Wifi, 1.18RC2.

    M106 P1 S1; Fan runs at 100%
    M106 P1 S0; Fan runs slowly making unhappy noises.

    I've tried playing around with other parameters - it didn't work and shouldn't S0 be the only thing I need to disable power?

    When I moved the connector over to FAN0 or FAN2, S0 and S1 work. It's just FAN1.


  • administrators



  • Sorry, thought I had disabled thermostatic mode, but "M106 P1 H-1 S0" is working now so I must not have. To be honest I found the fan configuration a bit confusing.

    Here are some of the things that tripped me up (that I don't believe are mentioned in the documentation):

    • Fan 1 (but not Fans 0 or 2) is initially set to Thermostatic Mode by the firmware. I did not expect that the defaults for one fan would be different than the other two - I thought setup would be done in config.g.

    • In Thermostatic Mode, The S parameter works for values of 128 through 255, but all values of S < 128 are treated as S128. (That's the main thing that led me down the wrong path.)

    • When in Thermostatic Mode and above trigger temp, after an attempt to set S<128 (say "M106 P1 S64 T15"), "M106 P1" will report that fan speed is 25%, even though the fan is actually spinning with a 50% duty cycle.

    • Similarly, when in thermostatic mode and above trigger temp, after an attempt to turn the fan off (say "M106 P1 S0), "M106 P1" will report that fan speed is 0%, even though fan is actually spinning with a 50% duty cycle.

    • "M106 P1 I-1" does disable the fan, but "M106 P1 I0" doesn't re-enable it. I couldn't figure out how to re-enable it without a reset.


  • administrators

    Thanks for the feedback - I will look at the documentation. The point about defaults being different for different fans is well made, maybe we should revisit this in future versions of the firmware.



  • Happy to help!


  • administrators

    The default for Fan1 is different both in hardware and firmware. This is so that you can use it to control the hot end fan, safe in the knowledge that if anything goes wrong, or you upgrade firmware while the hot end is still hot, the fan will run so your hot end will not get jammed with melted filament.



  • That's what I figured - I just didn't see it in the docs so I was confused.

    But I would have thought Fan0 would be the hot end fan - is Fan0 normally controlling something else (like print cooling)? Would like to assign my fans the same way as everyone else.


  • administrators

    Fan0 is the print cooling fan by default - it's the most important one to be able to control.

    The default configuration of Fan1 is documented at https://duet3d.com/wiki/Connecting_and_configuring_fans.


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