Heating bed moves after switching off

  • when I turn off the printer, the heating bed moves
    by its weight down and the stepper motor turns.
    it takes 6.5sec for 27cm.
    (Belt drive with gear ratio 3,125, stepper 0.9°)

    Is the resulting current / voltage dangerous for the board?


  • administrators

    Hi Hein

    David may be able to comment further but without knowing quite alot of details about your motor/s and then alot of calculations it is hard to give you an exact answer. As the motor/s are turned by the falling bed for quite a long time, one option would be to measure the voltage generated to see if it was above the maximum for the drivers in a powered down state. From the data sheet:

    Absolute maximum ratings:
    Supply voltage 30 V
    Supply voltage when disabled 60 V

    Are you seeing sufficient voltage being back fed to get anywhere near these numbers?

  • administrators

    Assuming that your bed heater is powered from VIN, it might help to rig up a relay to bypass the bed heater mosfet when the power is turned off. Then the bed heater will be connected across VIN when the power is off. This will help dissipate the power that the motors generate. It should also act as as brake on the motors, causing the bed to fall more slowly.

  • I'll be back at my printer tomorrow and see what I can do.
    I will report then.

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