DRV8825: Input and output power

Renan,

A stepper motor mechanical output power is torque multiplied by speed.  The total stepper motor system efficiency is usually mechanical output power (w*T) divided by electrical input power (U/I). Also,  the torque is provides by the stepper motor driver should be higher than the system needs to make sure no step pulse missing.

When you talked about DRV8825 efficiency, you may only want to know the power dissipation of DRV8825. In this case, “Calculating Motor Driver Power Dissipation” application note( http://www.ti.com/lit/an/slva504/slva504.pdf ) gives an example.

DRV8825 driver is a current source and provides different step current according to the micro-step setting and  full scale current setting. Since the output current and voltage both are changed on every micro-step, I would make s simple case to help on power dissipation estimation or measurement. First, hold the motor not move. If the micro-step setting sets a sine waveform to the motor winding, we can use scope to get the RMS value of that sine waveform. Since the motor is stall, there is no back EMF, use Irms*Irms*Rwinding to estimate the output power. And then, compare it with the input power to get the power dissipation measurement.