Stepper motor ‘voltage’ is an often confusing subject. Many motor drivers use widely varying bus voltages to operate stepper motors. In fact, identical stepper motors can be (and commonly are) operated at greatly different voltages in different systems. How can the same motor be run at different voltages? How does the bus voltage impact the stepper motor’s performance?
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Current and torque – Some Background
Stepper motors come with a nameplate current rating, winding resistance, output torque, and voltage rating. The important value is the current rating. Torque is generated proportionally to the winding current. The current rating on the nameplate is the winding current required to produce the rated torque output of the motor. So where does the nameplate voltage ‘rating’ come from?
The voltage ‘rating’ of the motor is simply derived from the motor’s rated current and winding resistance. An example motor shown above is rated for 5 A (per winding), with a winding resistance of .5 Ω. The motor’s nameplate voltage is therefore listed as 2.5 V
This is the voltage that produces 5 A of current into the winding in a steady state. However, a stepper motor must change the current in its windings rapidly and will not always run in a steady state. Unfortunately, inductance is associated with the winding (since it is a large coil of wire). The winding inductance prevents current from changing instantaneously and will require time to increase the current flowing through the winding after a voltage is applied to it.