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“How To Tell When Your Motor Capacitor Goes Bad
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?

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.

Start 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.

Run 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.

The 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.

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.

Still Experiencing Problems With Your Capacitor?

Pumps Plus of Cape Coral is the leading service provider for electrical motors in Southwest Florida.

What’s the Difference between a Start and a Run Capacitor?
A capacitor is an energy storing device. It is a medium by which energy is stored to either be released suddenly or over a period of time. The energy or capacitance of an electric capacitor is measured in the form of micro-farads. Essentially, two plates are separated by a material known as a dielectric or insulator. These insulators can be mica, ceramic, porcelain, Mylar, Teflon, glass, or rubber. Capacitors will also limit the current. They can be used to store voltage or build it up until the call for it to be released is present.

A start capacitor is found in the circuit of start windings when the motor is starting. This capacitor contains a higher capacitance than a run capacitor. It varies, but a start capacitor will measure between 70 and 120 micro Farads. The start capacitor provides an immediate electrical push to get the motor rotation started. Without a start capacitor when the voltage is applied, the motor would just hum. The start capacitor creates a current to voltage lag in the separate start windings of the motor. The current builds up slowly, and the armature has an opportunity to begin rotating with the field of current.

A run capacitor uses the charge in the dielectric to boost the current which provides power to the motor. It is used to maintain a charge. In AC units, there are dual run capacitors. One capacitor provides power to the fan motor. The other sends power to the compressor. Run capacitors measure in at approximately 7-9 micro-Farads. The value or rating of the run capacitor must be accurate. If the value is too high, the phase shift will be less than perfect and the winding current will be too high. If the capacitor value/rating is too low, the phase shift will be higher and the winding current will be too low. If run capacitors are not ideal, then the motor could overheat and the true torque will not be enough to drive current.

Capacitors
The schematic symbol for a capacitor actually closely resembles how it’s made. A capacitor is created out of two metal plates and an insulating material called a dielectric. The metal plates are placed very close to each other, in parallel, but the dielectric sits between them to make sure they don’t touch.

The dielectric can be made out of all sorts of insulating materials: paper, glass, rubber, ceramic, plastic, or anything that will impede the flow of current.

The plates are made of a conductive material: aluminum, tantalum, silver, or other metals. They’re each connected to a terminal wire, which is what eventually connects to the rest of the circuit.

The capacitance of a capacitor — how many farads it has — depends on how it’s constructed. More capacitance requires a larger capacitor. Plates with more overlapping surface area provide more capacitance, while more distance between the plates means less capacitance. The material of the dielectric even has an effect on how many farads a cap has. The total capacitance of a capacitor can be calculated with the equation:

Where εr is the dielectric’s relative permittivity (a constant value determined by the dielectric material), A is the amount of area the plates overlap each other, and d is the distance between the plates.

Electric current is the flow of electric charge, which is what electrical components harness to light up, or spin, or do whatever they do. When current flows into a capacitor, the charges get “”stuck”” on the plates because they can’t get past the insulating dielectric. Electrons — negatively charged particles — are sucked into one of the plates, and it becomes overall negatively charged. The large mass of negative charges on one plate pushes away like charges on the other plate, making it positively charged.The positive and negative charges on each of these plates attract each other, because that’s what opposite charges do. But, with the dielectric sitting between them, as much as they want to come together, the charges will forever be stuck on the plate (until they have somewhere else to go). The stationary charges on these plates create an electric field, which influence electric potential energy and voltage. When charges group together on a capacitor like this, the cap is storing electric energy just as a battery might store chemical energy.

Electric Motor Starting Capacitor Selection
Electric motor start-run capacitor selection guide:

This article explains how to select an electric motor start capacitor, hard start capacitor, or run capacitor that is properly rated for and matches the requirements of the electric motor such as an AC compressor motor or fan motor where the capacitor is to be installed.

This electric motor capacitor article series explains the selection, installation, testing, & use of electric motor starter start and run capacitors used on various electric motors found in or at buildings such as air conditioner compressors, fan motors, some well pumps and some heating equipment.

These electric motors use a capacitor to start and run the motor efficiently. We also explain the choice & wiring procedures for a hard start capacitor designed to get a hard-starting air conditioner compressor motor, fan motor, refrigerator, or freezer compressor or other electric motor (such as a well pump) going.

Capacitance is the ability of a device to store an electrical charge.

An electric motor capacitor is a device that first stores, then releases an electrical charge to help start an electrical motor (starting capacitor) or to keep it spinning (run capacitor) – the electrical charge or potential energy stored in the capacitor is used to give a power boost to the motor to help it overcome inertia – to start rotating.

The higher a capacitance or µF, the greater the total voltage charge that will be accumulated and then released by the capacitor to give the motor a “”kick”” to start it rotating.

Before trying to replace a capacitor, you should know that some motors use a combined start/run capacitor and others don’t use a start or run capacitor at all.

The Role of Capacitors
The capacitors are an essential part of your air conditioning system. The capacitors are small cylindrical shaped containers that lie inside the housing of the air conditioner. The main purpose of them is to store energy and provide it to the motor upon start-up and when running. They are called a start capacitor and a run capacitor.When your air conditioner first turns on, it requires a massive amount of energy to begin its cycle. Often, your home’s electrical system can’t handle the large load of energy needed to get the system going. This is where the start capacitor comes in. Once the AC is turned on, the start capacitor sends an immediate electrical charge, or boost, to get the rotation of the motor started. Once the proper amount of torque, or energy, is pushed to the motor, then the start capacitor shuts off.

Once the system has started and is operating, the run capacitor takes over and provides the extra power to run the air conditioner for long periods of time. When the air conditioner is running, both capacitors create and store energy for the push for the next cycle. Many air conditioning systems, as well as heat pumps, use a dual capacitor system which connects both the start and run capacitors to the compressor and fan motors.

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