Fan 0 either giving 0V or 5V



  • So i'm trying to setup the part cooling with fan0.

    i have setup fan0 as such:

    M563 P0 D0 H1 F0
    M106 P0 S0 I0 F11000 H-1

    When measuring with the multimeter, I get very weird results

    S0 0V
    S1 5V
    S0.1 5V
    S0.2 5V
    S100 5V
    S200 5V

    So it seems to be only fully on, or fully off. and I can't seem to make any sense of it.

    I've added the config.g file

    0_1553003302261_config.g


  • administrators

    What sort of fan is it? You are using a high PWM frequency, F11000. If the fan has a smoothing capacitor built into it, that and the high PM frequency might explain the problem.



  • I'm using a three phase brushless DC fan with a speed controller. The speed controller is usually controlled by a pot meter (5v output, speed control signal in, ground). The manufacturer says that it requires a 10khz or higher PWM signal to control the fan.

    It's connected as such:
    0_1553006592437_fan control.jpg

    It's connected to fan0 on the duet board. The red wire on the bottom is +5v output, which is adjusted by the potmeter via the gray cable. I was not having any luck with this setup, so I hooked up a multimeter to the duet, and was getting the readings mentioned above.


  • administrators

    You may need to add a pullup resistor between the Duet Fan- pin that feeds the ESC and +5V. Try 1K.



  • I think that I broke the MOSFET controlling the FAN0 output. whatever gcode commands I send I try it doesn't change really. Either 5V or 0V.

    FAN2 does work, but the output voltage only goes between 2.5V and 5V, not betwee 0-5V, is that correct?

    1.0 : 4.97V
    0.9 - 4.97V
    0.8 - 4.93V
    0.7 - 4.83V
    0.6 - 4.66V
    0.5 - 4.43V
    0.4 - 4.14V
    0.3 - 3.81V
    0.2 - 3.44V
    0.1 - 3.02V
    0.0 - 0V



  • Don't the fan mosfets control the negative side? The amount of voltage output is what the VFAN is set to, it just has a frequency of off/on The mosfets don't do variable voltage.



  • Ah, I must have misunderstood what mosfets are for. In any case, something seems to be broken on the FAN0 side, and the FAN2 doesn't seem to be able to go below 3v (which is a real shame, I'd like to run the fan around 1-2v)



  • @comediantf2 You still don't understand what mosfets do. You fan output never goes anything below VFAN (in you case 5V), they just switch very fast on and off between 0V and 5V and changing the "output" is just changing how much time is the on time compared to off time.
    So they is no variable voltage on any fan output, that values with you get com only from that that you multimetter does some averaging when taking measurements. And probably this is not perfectly linear that is why you don't get any thing below 3V.



  • @comediantf2 As others have been trying to point out, the fan speed is adjusted using PWM, not by varying the voltage. PWM stands for Pulse Width Modulation - look it up but here is a Wikipedia link https://en.wikipedia.org/wiki/Pulse-width_modulation



  • Thanks everyone, that makes a lot of sense. Will do more reading!


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