Repeatedly blown fan FETs

  • I'm driving some pretty substantial solenoids with Fan 0, 1, and 2 circuits. They draw 1.5A at 24V (16.2 DCR). They'll work for quite a few cycles, but eventually latch up the FET (which unfortunately also melts the solenoid.) Any way to get beefier FETs on the next rev. of the Duet boards?

    Side question - any way to prevent these circuits from blipping on at startup?

  • you need to put a flyback diode across the positive and negative of the fans to prevent the voltage spikes that are destroying the mosfets.

    The fan outputs were designed for small brushless fans like what you would see on a hotend..

  • administrators

    The 1.02 and later revision Duet PCBs have built-in flyback diodes. The earlier ones don't.

    Are you fan-cooling the area of the board with the fan mosfets? At 1.5A continuous current they will get hot if you don't.

    Fans 0 and 2 shouldn't blip on startup. Fan 1 will because it defaults to being on, for maximum safety when it is used to control the hot end heatsink fan.

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