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How To Tell When Your Motor Capacitor Goes Bad
Jan. 30, 2023

If you're reading this, then you probably suspect there's something wrong with your motor capacitor.

Are you wondering how to tell if your capacitor is failing?

In this helpful article, you will find out:

- What a capacitor is

- What a capacitor does for your motor

- The two main types of motor capacitors

- How to tell if your capacitor is bad

First, let's talk about what a capacitor is and what it does for your motor.


What Is A Capacitor?

Ceramic Capcitor

Ceramic Capacitor

A capacitor is a device that stores electricity. It can be large or small depending on its use. Capacitors can be found in anything from an electronic circuit to a power plant.


What Does A Motor Capacitor Do?

Single-phase motors use capacitors to help get them started and for energy saving.

There are two main kinds of motor capacitors:

1. Start Capacitors

2. Run Capacitors

Now that you know the two main types of motor capacitors, let's talk about what each kind of capacitor does and how it affects your motor.

ㆍStart Capacitors

A start capacitor is used to give a motor an extra electrical push to start it turning. A start capacitor is only used in the motor circuit for a second or two when it first starts to turn.

Once the motor is up to speed, the start capacitor disconnects and is not used again until the next time the motor starts. If the start capacitor fails, then the motor will not be able to begin turning.

ㆍRun Capacitors

A run capacitor is an energy-saving device that is in the motor circuit at all times.

If a run capacitor fails, the motor can display a variety of problems including not starting, overheating, and vibrating. A bad run capacitor deprives the motor of the full voltage it needs to operate correctly.

ㆍThe Difference Between Start And Run Capacitors

Both start and run capacitors are made the same way, but run capacitors are much more heavy-duty than start capacitors since a run capacitor is always used when the motor is running.

For this reason, you cannot use a start capacitor to replace a run capacitor. Motors can use one or both types of capacitors depending on what they are designed to do.

Radial Aluminum Electrolytic Capacitors

Radial Aluminum Electrolytic Capacitors

Capacitor Failure: Is Your Capacitor Bad?

When you suspect you have a bad capacitor, there are a few motor capacitor failure symptoms you should look out for.

*Signs Of A Failing Capacitor

- Your motor starts slowly

- Your motor won't stop buzzing

*It's Not Your Capacitor When...

If your motor is completely dead (does not move and does not make any noise at all), then the problem is more than a capacitor.


How To Test Your Capacitor

Do you want to determine whether your capacitor is working properly?

You can test your capacitor using a high-quality electrical meter.

The unit of capacitance is microfarad. Capacitors are labeled with what microfarad value (abbreviated mfd or uf) that they should be.

If your electrical meter displays a microfarad value that is too high or too low, this is a sign that your capacitor is bad.

Before testing your capacitor, be sure to short across the terminals with an insulated handle screwdriver. This will help you remove any stored power.

The capacitor value needs to be within the labeled range for it to be any good.

Keep in mind capacitors do not have any polarity so it does not make any difference which side the wires go on.

However, if you had more than two wires going to the capacitor, the wires that are paired together on one side must always be paired together.


Capacitor Safety Reminder

As with any electrical device, disconnect the power to the motor before servicing it and discharge the capacitors before handling them. We are a capacitor supplier. If you are interested in our products, please contact us now!