VIN under-voltage event (8.0V) when driving motor



  • Hello,

    We have a problem when we try to drive our stepper motor. When we click on the web interface on e.g. X+1, the message "VIN under-voltage event (7.5V)" appears. The motor move a little bit and then it's impossible to send another command. We have checked VIN and it's always to 24V. Max current is 2A and our motor needs only 1.7A max.
    We don't have any heating stuff, only one motor connected to the duet. Fuse are OK.

    Is a problem in our parameters? We have set x16 microstepping and 16steps/mm. Maybe the speed is too fast? Same problem appears with each drivers.

    Thanks for help



  • It sounds like a power supply issue. Have you tested the voltage with a load on it? The motors don't draw much current, so shouldn't really put much load on a PSU. Could also be wiring; check the power wires are firmly screwed into the screw gates of the power terminals on the Duet (it's quite easy to miss the screw gate so the wire is just floating about in the terminal) and at the PCU end.

    Ian



  • @droftarts thanks for your answer!

    I don't think its the connectors... The led is always on.
    I'll check the power supply, but actually I use a lab power supply, with 2A output max. Could it be a problem?



  • @DoRo said in VIN under-voltage event (8.0V) when driving motor:

    @droftarts thanks for your answer!

    I don't think its the connectors... The led is always on.
    I'll check the power supply, but actually I use a lab power supply, with 2A output max. Could it be a problem?

    Possible, although I'm no expert regarding stepper motors. Have you tried using M906 to reduce the current to see if that improves things?



  • @DoRo A 2A PSU? Quite possibly! You can calculate how much current you need. See these pages:
    Use this page to work out how much power your stepper motor needs:
    https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors
    Use this page to work out the PSU requirements
    https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply#Section_Total_power_needed
    My guess is that the following is causing too much strain on your PSU:

    Stepper motors: at full rated current, the power needed for each motor is its rated current times its rated voltage (if no rated voltage is specified, use the square of the rated current times the phase resistance). This is the power at standstill. To allow for driver losses and the extra power needed to create acceleration, add 50%. Multiply by the number of stepper motors.

    Ian



  • The motor current was already at 300mA... And it's the minimal value I can set in RepRap firmware.



  • @droftarts I'll try it tomorrow

    Thanks



  • @droftarts Hello,

    So today I've try to use a 240W power supply (12V, 20A). The message I had yesterday doesn't appears any more.

    Yet, the motor make a step forward, then, a step backward, another step backward, and finally a step forward to come in start position.

    Do you have an idea what's going wrong?

    Thanks



  • Sounds like a motor phase isn’t connected, so it’s just oscillating back and forth. Possibly a poorly crimped crimp in the connector housing. Disconnect the motor from the Duet, check for continuity at the connector. Of the four pins, there should be continuity between pin 1 and 2, and between pin 3 and 4; doesn’t particularly matter which end you count from!

    If that doesn’t show up the fault, tTo diagnose further, will probably need to see your config.g, and the motor make, model and specs. Pictures of the wiring might help, too.

    Ian


  • administrators

    If your are getting under-voltage events when you try to move the motor, and your PSU is rated at 2A, then here are some possibilities:

    • Faulty power supply
    • Motors connections not phased properly. How have you connected the motor to the Duet?
    • Blown stepper driver

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