Single Phase Motor Running Capacitor

4 min read Jun 26, 2024
Single Phase Motor Running Capacitor

Single Phase Motor Running Capacitor: Understanding the Basics

What is a Single Phase Motor?

A single phase motor is a type of electric motor that operates on a single phase power supply. It is commonly used in household appliances, industrial equipment, and other applications where a three-phase power supply is not available. Single phase motors are designed to operate on a single voltage supply, typically 120V or 240V, and are widely used in applications such as:

  • Fans and Blowers
  • Pumps and Compressors
  • Refrigeration and Air Conditioning Units
  • Washing Machines and Dishwashers

What is a Running Capacitor?

A running capacitor is a type of capacitor that is designed to improve the performance of a single phase motor. It is connected in series with the motor windings and helps to improve the motor's efficiency, power factor, and starting torque.

How Does a Running Capacitor Work?

A running capacitor works by providing a reactive current to the motor windings, which helps to:

  • Improve Power Factor: The capacitor helps to correct the power factor of the motor, which is the ratio of the real power to the apparent power. A higher power factor results in more efficient operation and reduced energy losses.
  • Increase Starting Torque: The capacitor provides a high starting current to the motor, which helps to overcome the inertia of the load and improve the motor's starting torque.
  • Reduce Energy Losses: The capacitor helps to reduce energy losses in the motor windings, resulting in improved efficiency and reduced heat generation.

Types of Running Capacitors

There are two main types of running capacitors:

  • Paper Capacitors: These are the most common type of running capacitor, made from paper dielectric materials and oil-impregnated.
  • Film Capacitors: These are more expensive than paper capacitors but offer improved performance and longer lifespan.

Selection and Sizing of Running Capacitors

The selection and sizing of a running capacitor depend on several factors, including:

  • Motor Rating: The capacitor must be sized to match the motor's rating, including its voltage, current, and power factor.
  • Motor Type: The type of motor, such as induction motor or synchronous motor, affects the capacitor's selection and sizing.
  • Application: The application of the motor, such as fan, pump, or compressor, affects the capacitor's selection and sizing.


In conclusion, a single phase motor running capacitor is an essential component in improving the performance and efficiency of single phase motors. By understanding the basics of running capacitors, including their types, selection, and sizing, engineers and technicians can design and install more efficient and reliable motor systems.

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