There are indeed single-phase motors that do not require a capacitor to start. These motors are known as shaded-pole motors.

Starting Mechanism of Shaded-Pole Motors

Shaded-pole motors utilize a unique stator design to create a rotating magnetic field without using a capacitor for phase shifting. Here's how it works:

Shading Coil

The stator of a shaded-pole motor has a main winding and a smaller winding called a "shading coil." The shading coil is located in a portion of the stator and offset from the main winding.

Induced Magnetic Field

When the main winding is energized, it creates a magnetic field that rotates around the stator.

Phase Shift

The shading coil has a low inductance compared to the main winding. When the main winding is energized, the current in the shading coil lags behind the current in the main winding due to the inductive nature of the shading coil.

Asymmetrical Magnetic Field

This lag in current creates an asymmetrical magnetic field in the shaded region of the stator. The magnetic field is stronger in the shaded region and weaker in the unshaded region.

Rotating Magnetic Field

The asymmetrical magnetic field creates a force that tends to align the rotor with the strongest part of the field. As the rotor rotates, the magnetic field shifts, inducing a continuous rotating force in the rotor.

Advantages of Shaded-Pole Motors



Capacitor not required

Shaded-pole motors do not require a capacitor to start, which makes them simpler and more cost-effective.

Low starting torque

These motors have a low starting torque, making them suitable for applications where a gradual start-up is desired.

Widely used: Shaded-pole motors are commonly used in household appliances, such as fans, blowers, and small pumps, where starting torque is not critical. Flag for review