The rated current of a stepper motor refers to the maximum continuous current that each phase winding can safely carry in a static (locked-rotor) state. In other words, it is the maximum phase current at which the motor can operate continuously without exceeding its safe temperature limit. Modifying the coil specifications of the windings changes the motor's rated current, and STEPPERONLINE offers such customization services.
However, customizing the rated current is not simply a matter of adjusting a single specification. It has cascading effects on multiple core performance characteristics of the motor, most notably its speed–torque behavior. The following is a brief explanation covering low-speed and high-speed torque:
- Low-Speed Torque: In the low-speed region, torque is primarily proportional to current. A motor with a higher rated current generally delivers higher holding torque and low-speed torque. Conversely, a motor with a lower rated current typically provides lower holding torque and low-speed torque.
- High-Speed Torque: This is the area most significantly affected. The inductance of the windings opposes rapid changes in current. A high-current motor (wound with fewer turns of thicker wire) has lower inductance, allowing the current to build up more quickly.
As a result, during high-speed operation—when the pulse duration for each step becomes shorter—the coil current in a low-inductance, high-current motor can reach its rated value more quickly within the available energization window. This results in less torque drop-off at high speeds and better overall high-speed performance. Conversely, a low-current version (wound with more turns of thinner wire) has higher inductance. At high speeds, the current rises more slowly, causing torque to drop off rapidly.
Important Considerations: Increasing the rated current also increases power dissipation (I²R losses), which leads to higher motor operating temperatures. A higher-current motor may also require a driver with greater current capacity and can exhibit more pronounced resonance at low speeds. Please consult with our engineering team to ensure the customized motor matches your application requirements and driver capabilities.