How Do You Test An Electric Motor Capacitor

5 min read Jun 26, 2024
How Do You Test An Electric Motor Capacitor

Testing an Electric Motor Capacitor: A Comprehensive Guide


Electric motor capacitors play a crucial role in the functioning of many electrical systems, including air conditioners, refrigerators, and pumps. A faulty capacitor can cause the motor to malfunction or even fail, leading to costly repairs and downtime. Therefore, it is essential to test an electric motor capacitor regularly to ensure it is functioning properly. In this article, we will discuss the steps to test an electric motor capacitor.

Precautions Before Testing

Before you start testing the capacitor, make sure to take the following precautions:

  • Disconnect Power: Ensure that the power supply to the motor is turned off to avoid any electrical shocks or injuries.
  • ** Wear Protective Gear**: Wear rubber gloves and safety glasses to protect yourself from electrical shock.
  • Use a Multimeter: A digital multimeter is the ideal tool for testing capacitors.

Testing the Capacitor

Visual Inspection

Perform a visual inspection of the capacitor to check for any signs of physical damage, such as:

  • Cracks or Breaks: Check the capacitor case for any cracks or breaks.
  • Swollen or Bulging: Check if the capacitor is swollen or bulging, which could be a sign of internal damage.
  • Burn Marks: Check for any burn marks or signs of overheating.

Capacitance Measurement

Use a digital multimeter to measure the capacitance of the capacitor. Set the multimeter to the capacitance measurement mode (usually denoted by the symbol "Cx" or " Capacity"). Touch the multimeter leads to the capacitor terminals and take the reading. Compare the reading with the value specified on the capacitor label or in the manufacturer's documentation.

ESR (Equivalent Series Resistance) Measurement

ESR is an important parameter that measures the internal resistance of the capacitor. A high ESR value indicates a faulty capacitor. Use a digital multimeter with an ESR measurement function to take the reading.

Capacitor Leakage Test

This test checks for any leakage current in the capacitor. Set the multimeter to the ohms (Ω) function and touch the leads to the capacitor terminals. A good capacitor should show a high resistance reading (usually in the range of megohms). A low resistance reading indicates a faulty capacitor.

Capacitor Voltage Test

This test checks if the capacitor can hold a charge. Apply a voltage to the capacitor (usually the rated voltage) using a variable power supply. Measure the voltage across the capacitor using a multimeter. A good capacitor should hold the charge and show a steady voltage reading.


Testing an electric motor capacitor is a relatively simple process that can help you identify any faults or issues with the capacitor. By following the steps outlined in this article, you can ensure that your motor is running efficiently and effectively. Remember to always take the necessary precautions when working with electrical systems to avoid any accidents or injuries.

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