How To Test A Motor Starting Capacitor

5 min read Jun 26, 2024
How To Test A Motor Starting Capacitor

How to Test a Motor Starting Capacitor

A motor starting capacitor is a crucial component in the operation of electric motors, particularly in single-phase induction motors. Its primary function is to provide a high voltage pulse to the motor windings during startup, enabling the motor to overcome its initial inertia and start rotating. Over time, the capacitor can deteriorate or fail, leading to motor malfunction or failure. Therefore, testing the capacitor is essential to ensure the motor operates efficiently and safely. In this article, we will guide you on how to test a motor starting capacitor.

What You'll Need

  • A multimeter (digital or analog)
  • A capacitor tester (optional)
  • The motor starting capacitor

Step 1: Visual Inspection

Before performing any tests, inspect the capacitor for signs of physical damage, such as:

  • Cracks or breaks in the casing
  • Burns or rust on the terminals
  • Signs of moisture or corrosion

If the capacitor shows any of these signs, it's likely faulty and should be replaced.

Step 2: Measure Capacitance

Use a multimeter to measure the capacitance of the capacitor. Set the multimeter to the capacitance measurement function (usually denoted by the "C" symbol). Attach the multimeter leads to the capacitor terminals, ensuring correct polarity (red lead to the positive terminal and black lead to the negative terminal).

Record the capacitance reading and compare it to the manufacturer's specifications or the capacitance value printed on the capacitor. If the reading is significantly lower than the specified value, the capacitor may be faulty.

Step 3: Measure Resistance

Measure the resistance of the capacitor using a multimeter. Set the multimeter to the ohms (Ω) function. Attach the multimeter leads to the capacitor terminals, ensuring correct polarity.

A good capacitor should have a very high resistance, typically in the megohm range (MΩ). A low resistance reading may indicate a faulty capacitor.

Step 4: Perform a Capacitor Test (Optional)

If you have a capacitor tester, you can use it to perform a more comprehensive test. A capacitor tester applies a high voltage to the capacitor and measures its ability to hold a charge.

Follow the tester's instructions to perform the test. The tester will indicate whether the capacitor is functioning within specifications or not.

Step 5: Check for Leaks (Optional)

If the capacitor is an electrolytic type, you can check for signs of leakage by inspecting the capacitor's casing for signs of bulging or swelling. A leaking capacitor can be a sign of internal damage and should be replaced.


Testing a motor starting capacitor is a relatively simple process that can help you identify potential issues before they cause motor failure. By following these steps, you can ensure the capacitor is functioning correctly and the motor operates efficiently and safely. Remember to always follow proper safety procedures when working with electrical components.

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