I am looking at using a stepper motor retrieved from a photocopier.
It’s a 6 wire nema 23, 42mm long and a 1/4" shaft. Label says STP-59D1030, 1.8deg/step, 1.3ohm … of course I will run it as 4 wire. Never thought to look at the copier brand. Internet searches revealed nothing about it.
I have a circuit based on the drv8825 and supplied with 12v that I can use to run it but I can’t find out the stepper’s max current spec.
How do I go about doing that ? … Should I gradually increase the current until the motor gets hot, then back it off ? If so, what would be a good starting point ?
Yes, gradually increasing the current until the motor starts to get hot seems reasonable.You might also look at a few other similarly sized motors (with the same NEMA size and motor length), calculate the coil power for those (which is the rated coil voltage multiplied by the rated coil current), and then back-calculate the amount of current necessary to produce that power in your motor. That might provide a little more confidence you are using the motor in a reasonable way. It is generally acceptable to use a lower current than the motor’s current rating; doing so will just reduce the motor’s torque.
Many industrial type steppers are designed to run at temperatures as high as 80 C, which is too hot to touch. But if you smell burning insulation, stop.
