How to check motor capacitor

Capacitors in motors are mainly used for two purposes, one to provide starting boost, and second to keep the motor running smoothly. Similarly, for that purpose, two types of capacitors are used in this regard, one is called start capacitor, and the other is named run capacitor. If the motor is not running properly, such as having trouble starting or overheating after running for a period of time, it may be due to the motor capacitor.


How to check motor capacitor


How to check motor capacitor

Capacitors generally last a long time due to their internal structure, but their lifespan can be affected when subjected to high voltage or any surges. As mentioned above, motors have two capacitors per type of motor and if any one of the capacitors is bad it will affect the functioning of the motor. So, there are several ways to check the capacitors of the motor:

check capacitance value

The first thing to check the capacitor is to find out its actual capacitance value because sometimes the capacitor does not provide enough capacitance, which results in the motor failing. Therefore, to get the actual value of capacitance you must have a multimeter with the option to measure capacitance. Turn on the meter, move the dial to the capacitance symbol and connect the red lead of the multimeter to the positive terminal and vice versa:

Now look at the value of capacitance displayed on the meter and compare it with the printed limit for the value of capacitance on the capacitor. If the value falls under this range, it means the capacitor is in good condition, and if not, it needs to be replaced.

check resistance

The best way to check if a capacitor is burst or short-circuited is to check its resistance and if it shows infinite resistance then it means the capacitor is still good. So, to check the resistance you need a digital or analog multimeter, move the dial to the resistance symbol and connect the probes of the multimeter to the capacitor:

At first, the meter will show the resistance value increasing slowly and then suddenly it will go to zero, however if you are using a meter with auto ranging it will keep increasing. Now change the direction of the probe to see the resistance as the capacitor discharges:

If the resistance is increasing for both charging and discharging, it means the capacitor is not blown or short-circuited. Also note that in case of analog meter, it will show only deflection, which means the capacitor is not blown.

check capacitor voltage

Sometimes the capacitor does not hold charge or it has any problem while charging, in that case charge the capacitor and check its voltage through a multimeter. Here are some steps for this method:

Step 1: Discharge the capacitor completely

Typically, capacitors are not fully discharged, so it is necessary to fully discharge a capacitor in order to charge it for testing purposes. So, to discharge a capacitor, simply place a screwdriver between its positive and negative terminals:

Step 2: Charge the Capacitor

Since the motor runs on alternating current, it usually has a non-polarized capacitor, so connect the capacitor to the AC supply for just one second:

Step 3: Measure Voltage

Now to see if the capacitor has been replaced, simply place a screwdriver between the terminals of the capacitor and if there is a spark it means the capacitor is good:

On the other hand, use a multimeter to check the voltage on a capacitor, simply set the dial to voltage and connect the multimeter probe to the capacitor.

A digital multimeter connected to wires generates details automaticallyA digital multimeter connected to wires generates details automatically

If the voltage is somewhat close to the voltage of the power supply, it means that the capacitor is in good condition, and if not, it needs to be replaced.

Comment: Before trying all the above methods, it is important to completely discharge the capacitor using a screwdriver. Additionally, care must be taken when charging and discharging capacitors. Also, the methods for checking the start and run capacitors are the same.


Capacitors are passive devices that store electrical charge between their electrodes, and this energy can be used for many different applications. Firstly, it is used in motors, there are two types of capacitors in motors, one is start capacitor and the other is run capacitor. Some motors have both capacitors, while some have only the start capacitor.

To check a motor capacitor, disconnect it from the motor and find its actual capacitance value, check its resistance, or measure its voltage by charging it. If the capacitor does not perform well in any way, it means it has gone bad.

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By Ranjan