Increasing the Starting Torque of a Single-Phase Motor

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The torque of a single-phase motor can be changed by adding capacitors to the start or run winding of the motor. When the single-phase motor is used without capacitors, as has been shown in the diagrams presented so far in this section, the motor is called a split-phase motor.

When a start capacitor is connected in series with the start winding and centrifugal switch, the motor is called a capacitor start, induction run (CSIR) motor. When the motor has a start capacitor in series with the start winding and a run capacitor is connected permanently across the run and start terminal, the motor is called a two-capacitor motor or a capacitor start, capacitor run (CSCR) motor. If the motor has only a run capacitor connected permanently across the start and run winding, it's called a permanent split capacitor (PSC) motor. If the rotor of the single-phase motor is made of copper wire rather than a squirrel-cage rotor, it's called a wound-rotor motor or repulsion start motor.

The following sections will explain the operation of each of these motors.

Methods of reversing these motors are also presented with their diagrams. At the end of this section methods of troubleshooting each of these types of motors are provided. We hope to provide an understanding of how these motors operate and how their rotation is reversed. It will also help to understand the methods of reconnecting the motor to operate on dual voltage or dual speeds. This information is important when one must connect motor control devices to them such as reversing starters or dual-voltage starters.

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Split-Phase Motors