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How to Calculate a Stepper Motor Current

Stepper motors make fine movements by using only a few coils. In the simplest case a two-coil stepper motor driver alternates supplying power to only one of the two coils at any given time. The effective of this is to drive the rotor of the motor a few degrees in a particular direction. Since the motor has multiple coils, measuring the current requires measuring the average current between the two coils, since only one coil is on at a time.

Things You'll Need

Stepper motor circuit (operational)
Multimeter (current meter mode ammeter)

Instructions

- 1
  Disconnect one terminal of one of the stepper motor's coils and connect the ammeter in series with it. The controller should connect to one side of the ammeter while the other side connects to the disconnected wire attached to the stepper motor.
- 2
  Run the motor and observe the current use. Assuming the motor is under a fairly constant load and otherwise unchanging conditions, the current usage should also remain steady. Watch the meter's reading just to be sure and record it.
- 3
  Reconnect the wire that was previously disconnected and repeat the test for the other coil inside the stepper motor. The current usage should be the same, but regardless, it must be tested.
- 4
  Add the two current readings together, this is the total average current draw of the stepper motor.

Insects & Science