What Size Start Capacitor For 1hp Motor

6 min read Jun 26, 2024
What Size Start Capacitor For 1hp Motor

What Size Start Capacitor for 1HP Motor?

When it comes to selecting the right start capacitor for a 1HP motor, it's essential to consider several factors to ensure efficient and safe operation. In this article, we'll delve into the world of start capacitors and provide you with a comprehensive guide on how to choose the correct size for your 1HP motor.

What is a Start Capacitor?

A start capacitor is a critical component in electric motor circuits that provides a boost of energy to the motor during startup. It helps to overcome the initial inertia of the motor and provides the necessary torque to get the motor running. Start capacitors are designed to operate for a short duration, typically a few seconds, and then disconnect from the circuit once the motor reaches its operating speed.

Factors Affecting Start Capacitor Selection

Choosing the right start capacitor for your 1HP motor depends on several factors, including:

Motor Type

The type of motor you're using plays a significant role in selecting the correct start capacitor. Different motor types, such as induction, synchronous, or reluctance motors, require specific capacitor sizes and types.

Voltage and Frequency

The operating voltage and frequency of the motor also impact the start capacitor selection. Higher voltage motors require larger capacitors, while lower voltage motors can use smaller capacitors.

Motor Horsepower

The horsepower rating of the motor is another critical factor. A 1HP motor, for example, requires a smaller start capacitor compared to a 5HP motor.

Capacitor Type

There are two primary types of start capacitors: electrolytic and film capacitors. Electrolytic capacitors are more common and cost-effective, while film capacitors offer better performance and longer lifespan.

Sizing the Start Capacitor for a 1HP Motor

To determine the correct size of the start capacitor for a 1HP motor, you can follow these general guidelines:

** Rule of Thumb**

A common rule of thumb is to use a start capacitor with a capacitance value between 120-240 μF for a 1HP motor. However, this is just a rough estimate, and the actual capacitance value may vary depending on the specific motor and application.

Motor Manufacturer's Recommendations

The best approach is to consult the motor manufacturer's recommendations for the start capacitor size. They typically provide specific guidelines based on the motor's design and operating characteristics.


If you don't have access to the motor manufacturer's recommendations, you can use the following formula to estimate the start capacitor size:

Capacitance (μF) = (Motor Horsepower x 100) / (Line Voltage x Motor Efficiency)

For a 1HP motor operating at 230V with an efficiency of 80%, the calculation would be:

Capacitance (μF) = (1 x 100) / (230 x 0.8) ≈ 170 μF


Selecting the correct start capacitor size for a 1HP motor is crucial for efficient and safe operation. By considering the motor type, voltage, frequency, horsepower, and capacitor type, you can determine the right size start capacitor for your application. Remember to consult the motor manufacturer's recommendations and perform calculations to ensure you're using the correct capacitor size.


  • Always follow the motor manufacturer's recommendations for start capacitor size and type.
  • Choose a capacitor with a voltage rating that matches or exceeds the motor's operating voltage.
  • Ensure the capacitor is designed for the specific motor type and application.
  • Consult a licensed electrician or experienced technician if you're unsure about capacitor selection or installation.