What’s the difference between ac and dc stepper drives?

Drives for stepper motors can have inputs that are either ac or dc. What happens inside the drive is that the input signal is converted to a series of square wave pulses that are applied to the motor’s windings to power the motor and produce motion.

A pulse generation function in a PLC or PC can be delivered to a drive with a built-in controller that powers the stepper motor. (Image via Oriental Motor)

However, stepper motors themselves function as ac motors (they are generally considered to be asynchronous machines) because even a dc input is converted to a square wave to drive the individual motor windings. In the case of stepper motors, more applied voltage causes a faster current rise in the motor windings. So in general, higher ac voltage inputs will create more torque.

Oriental Motor’s AZ Series drives can accept either single-phase 100 to 120 Vac or single-phase or three-phase 200 to 240 Vac. (Image via Oriental Motor)

Pairing the right drive with the right motor is critical to optimal stepper motor performance. For instance, higher speeds can be obtained by faster switching rates. But this depends on the inductance in the motor windings. However, increasing the drive voltage helps to overcome this limitation but can also create issues with higher currents as well, which must be limited so as not to damage the motor windings.