How to connect PWM fan?

  • As I print mostly ABS, I want to add a filter to my chamber, will be using this design
    I have this fan from Noctua (24V model, as my VIn is 24V):
    This fan has a 3 phase motor with separate PWM input connector.
    I want to control this fan from the Duet board, so that for instance if I print PLA, the fan can stay off.
    Is it possible to drive the PWM input of the fan from the Duet knowing that input has a VMAX of 5V?
    I know I can drive the fan just using VIn and Gnd but I want to take advantage of Noctua's built-in PWM chip (

  • administrators

    I wasn't able to find a specification for the PWM input to that fan. If it's the same as the Intel PWM fan specification:

    1. Connect the fan power leads to an always-on fan connector, or to VIN and ground.

    2. Connect a small signal diode (e.g. 1N4148), cathode (stripy end) to the FAN- pin of your chosen fan connector on the Duet, anode to the PWM input lead on the fan. This prevents the PWM fan input getting more than 5V. It assumes that there is an internal pullup resistor on the PWM input.

    3. In the initial M106 command for that fan use parameters I1 (to invert the signal) and F25000 (to increase the PWM frequency to 25kHz).

  • Thanks David, yes it is intel spec.
    Will try this out en let you know if it works 🙂

  • David, just out of curiosity what is the point in connecting a small signal diode in series with FAN- pin? Where is a voltage grater than 5V (indeed any voltage at all) could come to PWM input from? As I see in Duet's schematics FAN- is just an open drain MOSFET output. BTW, that diode worsen noise tolerance of PWM signal.

  • administrators

    Good point, you could connect it directly. I was thinking of how we connected a PWM fan to the Duet 0.6, which has an LED connected to the fan output.

  • Yes, direct connection works just fine.
    Very happy with this silent but powerful fan 🙂

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