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Topic: Current vs load on a stepper motor (Read 165 times) previous topic - next topic

64GTO


Would there be any change in the current drawn by a stepper motor if the load dropped from 50% of the holding torque to zero while the stepper motor is rotating?

jremington

#1
Jan 14, 2018, 01:32 am Last Edit: Jan 14, 2018, 01:33 am by jremington
With a modern current limiting driver, the current in any one winding is always changing as the stepper rotates, regardless of load.

But the load makes no easily detectable difference in the current variation, or in the average current drawn from the motor power supply.

64GTO

This is not the case in a regular dc motor correct?

jremington

Correct.

Steppers generally don't rotate fast enough that the generated back EMF significantly affects the current draw.

MarkT

Would there be any change in the current drawn by a stepper motor if the load dropped from 50% of the holding torque to zero while the stepper motor is rotating?
No, the current in the motor is set by the controller, not the motor.  At high speed you'd see a change in
the current drawn by the controller from the supply, but it would be hard to interpret, and anyway you
couldn't get to high speed and still provide 50% of holding torque, the torque drops off much more
rapidly than that.

There is no easy way to determine mechanical properties from electrical measurements in a stepper,
unlike for DC motors.  Some controllers claim to do stall detection, but not very well and not at low speed.

If you want this sort of electrical measurement of mechanical properties you need a servomotor, not a
stepper.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

MorganS

The simple answer is "No."

The more useful answer is "What are you trying to do?"
"The problem is in the code you didn't post."

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