Pwm fans and pwm frequency on duex



  • Hi all!

    Having problems with print fans on my idex setup. I have a duex2 expansion board and want to use pwm fan 3 and 4 on the duex for those
    Had my fan allocation set up like this:

    ; *** Assign Fan Channels
    M106 P0 S255 T45 H1 ; Trigger hotend 1 (left) fan at 45 C (P0 is PWM Fan 0 on the Duet WiFi)
    M106 P1 S255 T45 H2 ; Trigger hotend 2 (right)fan at 45 C (P1 is PWM Fan 1 on the Duet WiFi)
    M106 P3 F10 ; Part cooling fan (P3 is PWM Fan 3 on the Duex2 10Hz)
    M106 P4 F10 ; Part cooling fan (P4 is PWM fan 4 on the Duex2 10Hz)

    I suppose I use difficult 24V 20x40x40 fans (bigbox parts) but it does not matter what F parameter I use, the fans stop at anything less than M106 S255
    M106 S254 makes them stop.. When I used only one print fan before I converted to idex i used one of the pwm ports on the duet wifi and that worked great at F10

    Duex voltage jumper is set for Vin (24V)

    Is the pwm frequency settable at all on the duex board? or have I made a wiring misstake…

    Cheers!

    /Björn



  • Assigned fans like this now:

    M106 P0 F10 ; Part cooling fan (P0 is PWM Fan 0 on duet wifi, 10Hz)
    M106 P1 S255 T45 H1 ; Trigger hotend 1 (left) fan at 45C (P1 is PWM Fan 1 on Duet WiFi)
    M106 P2 F10 ; Part cooling fan (P2 is PWM Fan 2 on duet wifi, 10Hz)
    M106 P3 S255 T45 H2 ; Trigger hotend 2 (right) fan at 45C (P3 is PWM Fan 3 on Duex)

    And this works much better, at least with print fan P2, the other one (that I have assigned to P0) seems faulty (could be the fan)
    So it seems that pwm freqency is not settable in this way on the duex board?


  • administrators

    The PWM frequency on the DueX board is fixed - it is a limitation of the I/O expander chip. We may in future allow unused heater outputs to be used to support fans, which would provide a variable PWM frequency.



  • Print fans working ok now! Had a bad solder on print fan assigned to P0, so for *difficult" pwm fans, do use P0 to P3.. For full on fans like extruder cooling fans, I guess the duex pins are ok (runs at full speed when needed)



  • Good catch, I'm now struggling with my bigbox blower fan. 255 works but 254 or less halts the fan.

    Where to find two wire 24V fans thats reported to work with PWM?



  • Harder than finding buck converters, to do 24v to 12v or 5v.



  • Hello david,
    can you tell me whats the PWM-frequency of the DUEX Boards? Thank you very much in advance!


  • administrators

    @strips:

    Good catch, I'm now struggling with my bigbox blower fan. 255 works but 254 or less halts the fan.

    Where to find two wire 24V fans thats reported to work with PWM?

    The fans I use came from an ebay UK listing very similar to this one: https://www.ebay.co.uk/itm/2pcs-24V-2Pin-40mm-10mm-New-Case-Fan-PC-Computer-Cooler-Fan-Dual-Ball-Bearing/222236475383?hash=item33be537ff7:g:Y3YAAOSwvR5aPhwq. I haven't yet found a 24V blower fan that works well with PWM.


  • administrators

    @L3DS:

    Hello david,
    can you tell me whats the PWM-frequency of the DUEX Boards? Thank you very much in advance!

    It's currently set to 488Hz. We could also choose 244Hz or 122Hz, but it would have to be the same for all fan outputs on the DueX.


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