Back Voltage on stepper drivers From Falling Z Axis

  • Hi All,

    Just wondered if measures are taken to stop the back emf from a falling z axis damaging the board? I'm in the final stages of replacing the OEM board from an Up Plus 2 with a duetwifi and have seen significant voltage generated when the platform falls. The Blue VIN light is lit brightly as the platform drops faster than I can drive it with the steppers to a hard stop.

    I'm wondering if I need to consider changes to protect the board?


  • Just to clarify the z-axis is belt driven.

  • administrators

    The voltage on the VIN rail must not exceed about 29V. If it's likely to go higher than that, you must use some sort of mechanical damper, or something to limit the voltage. One possibility would be an electronic switch that bypasses the bed heater mosfet, to turn the bed heater on (thereby loading VIN) if too high a voltage is detected.

    The Duet does have firmware protection to disable the stepper drivers if VIN exceeds 29V, but this doesn't act instantly so it would be unwise to rely on it.

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