What primarily determines the speed of a single phase motor?

The speed of a single-phase motor is fundamentally determined by the number of stator poles. This is rooted in the relationship between the motor's design and its operational frequency. The synchronous speed of an AC motor, including single-phase motors, can be calculated using the formula:

Synchronous Speed (RPM) = (120 x Frequency) / Number of Poles

In this formula, the frequency of the supply voltage influences the synchronous speed, but the specific number of stator poles plays a crucial role. Each pole pair set creates magnetic fields that alternately attract and repel, determining how fast the motor can turn. Therefore, increasing the number of poles decreases the synchronous speed, and vice versa.

While the load on the motor and the voltage applied can affect the operational characteristics and efficiency, they do not primarily define the fundamental speed at which the motor operates under no-load conditions. Understanding this distinction is essential for HVAC professionals when selecting or troubleshooting motors in various systems.