Stepper motors are resistant to rapid changes in current. This is because their coils make them inductive devices along with nay internal permanent magnets, if used in that type of stepper motor. Drives must be able to operate a stepper motor correctly given its intrinsic inductance properties. Some steppers are either designed for low speeds and others for higher speeds, which affects their inductance.
When operating at low speeds, stepper motors are usually rather unaffected by inductance. This is because current can easily flow through the motor windings quickly enough that the correct torque results. However, when operating at high speeds, a sufficient amount of current cannot reach the stepper motor’s coil windings before the next step. This reduces torque as the full capacity of the motor is not being utilized.
Drives can compensate for this imbalance if selected correctly. A drive that is capable of supplying higher voltages at higher speeds forces more current into the windings. This is because of Ohm’s law that relates current and voltage. This in turn allows the motor to maintain torque at higher speeds. For this to work, however, the drive must be able to ramp safely up the needed voltage. If engineers attempt to use a drive beyond its rated values, failure of the drive or motor is likely.
Furthermore, as mentioned, some stepper motors are better suited to higher speeds than others. Check the documentation to be sure. Trying to drive a stepper motor designed for low speeds with voltage levels for high-speed suited motors may cause overheating or failure. As a result, proper sizing and selection of a stepper motor and drive combination is vital. They should be selected with their relationship kept in mind. Ask manufacturers for drive and motor compatibilities and operating details.
For more information, read about the Stepper Motor Speed and Torque Relationship.
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