I have a stepper motor powered by a breakout board that uses the A4983 stepper motor driver (http://www.sparkfun.com/products/10735).
Sometimes when the power is disconnected and the drive wheels are back driven, all the LEDs on the the boards light up and it seems like the system is being powered by the stepper motors.
I have the board set up this way: Stepper motors connected to the stepper motor driver. Power coming from battery is directly hooked up to the driver's motor power supply. A 5v regulator comes off the same battery line and powers the micro controller and other 5v electronics.
Three questions:
1) what exactly is happening? I know when back driving the motor it will create a current, but this is a bipolar stepper, wouldn't the current be AC and thus destroy the circuit? (up until this point, everything still works just fine). How is the current flowing into my other electronics?
2) How harmful is this back driving? Are there serious voltage spikes that I should be worried about or is the stepper motor driver chip dealing with it?
3) how do i prevent or protect the circuits against harmful effects? I'd put a diodes between the motor driver and the motor but bipolar steppers are basically AC motors and that wouldn't work.
Best Answer
The voltage coming out of your motor probably is AC, but that is being rectified by the kickback catch diodes in the driver circuit. Assuming this circuit was designed and wired up correctly, only the correct polarity voltage will be fed back onto the DC power input net. As long at this voltage doesn't exceed what the circuit is rated to operate at, there should be no problem with this.