Confused about the Maximum Current for Stepper Drivers

  • I am a little confused about the maximum current that can be drawn by the stepper drivers on the Duet 2 Wifi and Duex5. In the documentation it says that there is a 7.5A fuse for both the stepper drivers and the hotend heaters. However, that amount of current, even without any hotend heaters, would only allow the stepper drivers to be run at 1.5A if they were all on at the same time. Have I missed something somewhere or am I correct?

  • administrators

    What you have missed is that when you use a switching constant current driver to drive a stepper motor, and the voltage needed by the stepper motor at the current you commanded is much lower than the VIN supply voltage (which is usually the case), then the actual current drawn from VIN is much less that the current flowing in the motor. For example, if the current is set to 1A and the motor needs 3V @ 1A but the supply voltage is 24V, then if the driver was 100% efficient then the current drawn form VIN would be (3/24) * 1A = 125mA. In practice the efficiency is a bit lower than 100%, which is why stepper drivers chips generate heat.

  • Ahh, thanks, I knew I had to be missing something.

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