What is the primary function of a motor "run" capacitor?

The primary function of a motor "run" capacitor is to help decrease amperage and slightly increase torque. In an alternating current (AC) motor, the run capacitor creates a phase shift between the voltage and current, which improves the motor's efficiency during operation. By optimizing the phase of the current, it enables the motor to deliver more torque while operating at a lower current draw, which is beneficial for performance and energy efficiency.

The run capacitor continuously operates during the motor's runtime, providing a more stable voltage and current to the motor windings. This helps maintain efficient operation and can also reduce heat generation from excessive current draw, which might otherwise lead to premature motor failure.

In contrast, other functions listed in the options such as increasing voltage input, providing emergency power backup, or acting as a cooling agent do not align with the core role of a run capacitor in a motor's operation. These functions are associated with different types of devices or components in electrical systems.