Issue with pwm fan output

  • I am using these 24v 40mm fans for my print cooling, and it doesn't seem to be behaving as expected with the M106 command
    (fans are these

    When I plug the fan into the always on pin, it spins at full speed as expected, when plugging into the PWM output FAN0, even when fan speed is set to 0% it still spins (very weakly), and doesn't seem to vary at all when adjusting the fan speed to 100%. I am guessing my config.g is incorrect in configuring the fan output but I can't figure out why.

    in my config.g code, i have
    M106 P0 S0.3 I0 F500 H-1

    is there anything I need to do to get pwm working? or is this fan somehow not compatible with the PWM output?


  • You don't need to configure Fan0, it defaults to PWM control.

  • administrators

    Some fans don't work well with the default PWM frequency, so you may need to try an F parameter lower than 500. However, full on and full off should work anyway. How are you adjusting the fan speed?

  • sooo, pretty sure i burnt out something during the initial install. IIf i disable thermostatic fan control for FAN1, it works as expected on that output in pwm mode, but FAN0 is busted. with it set to S0 it still outputs 24V. looks like the part that failed is labeled TR5 near the FAN0 header, it has a small black spot on it that the other mosfet controller FAN1 and FAN2 doesn't have :(, and during initial setup I somehow had something shorted while trying to get the fan working and heard a spark. Opps, ordering the part from digikey to replace 🙂

  • administrators

    Sounds like you may have shorted Fan0 out and blown the fan0 mosfet. Fortunately we added an extra resistor in the Duet WiFi design so that when this happens, it doesn't take the processor out with it.

  • administrators

    Tom, mosfet is a PMV40UN2

  • My fan0 just "broke" i hade a wire come lose on the fan most likely shorted it
    fan1 works but fan0 is dead
    can i use fan2 remap fan0 to fan2 ?
    or do i need to change "PMV40UN2"
    soldering on a new "PMV40UN2" will it fix my problem ?
    Thank you

  • administrators

    Hi if you have a fan channel spare its easiest to remap fan2 to function as fan 0.

    If you are using it as a thermostatic fan then you use M106 to map it to your heater (normally heagter 1 as the bed is heater 0)
    see here:

    If you are using it as a print cooling fan then setup your tool with it mapped to the correct tool (normally tool 0 for a single extruder printer):

  • found some more info on the web
    seam changing the "PMV40UN2" do fixe the problem 🙂
    but one more question
    can i take the "PMV40UN2" from fan02 and place it on fan0 for now while waiting for delivery on a new PMV40UN2
    if so do i need to solder back the broken one on fan02 or can i just leave it empty for now (im not using fan02)

    thank you

  • administrators

    Hi Jens

    Yes you can replace the PMV40UN2 mosfet but since you are not using fan 2 then 1 line of gcode will allow you to use fan2 in place of fan 0, this is probably a lot easier than replacing the mosfet.

    If you de solder fan 2 mosfet and use that to replace fan 0 it is fine to leave the fan2 location empty.



  • Thanks for a fast answer Tony (dident see it at first)
    add F2 to the tool 0 and im back in business
    Im so impressed with the duet board
    i killed my MSK Sbase last week i got this a few days ago and i just love it
    will never go back 🙂

  • Thanks again Tony 🙂

  • Hello again
    i have received the PMV40UN2 (i think. my have nr 72 on top the original have 64)
    i have only a normal solder set so it was a pain to get it in place and i may have damage it
    i only get 14v on a 24v system and its 14v always

    did i damage the PMV40UN2 or is it wrong version
    or something else i need to know

    This is the one i got

    Thank you

  • administrators

    That's the right mosfet. Small MOSFETs are quite easily damaged by static charge until they have been connected in place.

  • ok i have one more i will test that one 🙂
    Thanks for the help

  • haha they are relay small 🙂
    i got 3 of them and two of them jumped away in the installing process

    i also think i damaged the solder pads when removing the first one
    so its extra hard to get it in place

    i need to order 3 more and make a last try

  • administrators

    I don't advise trying to remove those mosfets without hot air desoldering equipment, because you need to heat all 3 pads at once.

  • well im learning by doing 🙂
    i did damage the 2 lower pads they are gone

    so i guess i have to live with it ?
    or can i connect them to something else ?

    this makes my magnet project a bit harder
    no i only have 2 fan ports and them are needed to the fans
    also the heater ports is all out
    can i use a external board/mosfet to control the magnet on/off(24v)
    or do i need to get a Duet2/5 board ?

    a hot air gun is on top of my shopping list now

    Thanks for the help

  • administrators

    If you are looking for an SMD hot air reworking station, the 852D+ isn't bad for a budget unit.

    If you look at the Duet WiFi schematic (see for links) then you can see which components the fan mosfet is connected to. You could glue the new mosfet dead bug style to the board and then use wires to connect it.

  • thank dc42
    been looking at the drawings and this looks correct to me
    see pic

    Please let me know what you think
    Thank you

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