The voltage rating of motor controller holding coils is typically:

• A. Not important if the control circuit is isolated
• B. Not necessarily the same as the motor supply voltage
• C. Always less than the motor supply voltage
• D. Always the same as the motor supply voltage

Answer: (B)

Holding torque comes from the current flowing through the coil, not from applying a fixed voltage. In motor controllers, the driver often regulates current (with PWM or a current-limiting strategy) rather than simply applying the motor supply voltage. Because of this, the voltage you use to drive the holding coil is chosen to achieve the needed current and torque, while staying within the coil’s insulation and design limits. That means the coil’s voltage rating does not have to match the motor’s supply voltage; it may be different depending on coil resistance, desired hold current, and heat management.