Guide On How To Test Motor Run Capacitors And Replace Them

Learn the steps required to properly test motor run capacitors on a farm. Before you start the test, you need to gather the tools you need to perform the capacitor test.

Electric multimeter with mode for continuity and capacitance testing. Continuity is identified as the sound logo and amplitude is identified by the capacitor logo (- || -) on the multimeter dial.

Capacitance meter to check the capacitance or operation of capacitors.

A set of multi-tool screwdrivers or sockets to open the motor's condenser housing.

Insulated pliers to remove the spade connector from the capacitor tab and retain the resistance to discharge.

An electrical resistor (15-20 kOhm) to dissipate the charge of the capacitor. The electrician uses an electrically insulated screwdriver to discharge the capacitor, which is not the recommended method.

Soldering iron (electric or gas pen) for removing and reconnecting the bleed resistor, if connected to the starting capacitor.

The procedure for removing the condenser from the motor

Turn off the power and make sure the engine you want to check (lockout-tagout) is disconnected. The best way to make sure the power is off is to physically disconnect the motor. However, they often have a waterproof switch that turns the fan off. It is also recommended to cut the circuit breaker of the motor.

Find the metal housing covering the starting and/or operating capacitors and remove it.

Use a screwdriver or multi-tool socket to remove the screws on both sides of the chassis.

After removing the cover, replace the screws in their original positions so that they do not get lost.

Before removing, take a picture of the capacitor label, wire color and position.

Remove the wire spade connector using insulating pliers, being careful not to touch the terminals. Capacitors cannot be connected to the motor for an accurate reading.

Use a 20 kOhm resistor (or a screwdriver) to connect the terminals of the capacitor to drain the charge. This should take up to a few seconds.

If the bleeder resistor is soldered between the tabs of the starting capacitor, then one leg of the resistor must be soldered from one tab to be able to measure the capacitance.

This is one of the most tedious steps in the process. Cutting the legs of the resistance with pliers may seem faster, but good motor run capacitors will make reconnection difficult.

Motor Capacitor Test

There are four tests to assess whether the motor run capacitors are good or bad. Use the Motor Capacitor Evaluation Worksheet at the end of this document to record the data collected for each capacitor tested. You and your team can print these worksheets to create a maintenance log for your farm.

Look for signs of capacitors exploding. If there were signs of the capacitor exploding, the relief port was eventually detonated. Or if the case is swollen, cracked, or corroded, stop and replace the capacitor.

Test the capacitor to make sure there is no electrical continuity inside the capacitor.

When using a multimeter, turn the dial to the continuity label. There is usually a sound wave symbol. Ensure that both ends of the multimeter are working by bringing them in contact with each other. You will hear a beep.

Put two leads on each of the reading terminals.

If you hear a beep, this means that the capacitor is defective because it is carrying current through the dielectric layer. Stop and replace the capacitor.

Test the capacitor for short circuits between the capacitor material and the case.

Skip this step if the capacitor housing is plastic.

When using a multimeter, turn the dial to the continuity label. There is usually a sound wave symbol. Ensure that both ends of the multimeter are working by bringing them in contact with each other. You will hear a beep.

Place one wire on the first tab and the second wire on the metal reading case. Repeat to see the second tab on the metal case.

If you hear a beep, this means that the capacitor is defective because it is passing current from the insulator to the case. Stop and replace the capacitor.

Capacitor capacitance test

If you are using an electrometer, convert the dial to the capacitance symbol (- || -). It is difficult to get good readings from some capacitive multimeters, and some multimeters may not have the ability to measure capacitance. You can use the amplitude meter to complete this test.

To test the capacitance, make sure the red and black leads are in place on the meter (if the meter has multiple plug holes). If there are red leads, they must be connected to the capacitance symbol.

Put two leads on each terminal for reading.

Capacitance measurements must be within the Microfarad (μF) rating on the label.

The starting capacitor should be within ±20 percent of the listed capacitance.

The operating capacitor should be within ±10 percent of the listed capacitance.

If the reading is at or outside these limits, stop and replace the capacitor.

MOTOR RUN CAPACITORS REPLACEMENT

If you determine that the operating one of the motor run capacitors is defective, you will need to replace the damaged unit with a new one.

Record label information for the test capacitor. Be sure to take a picture of the capacitor label or enter the information into the motor capacitor assessment worksheet.

The capacitance ratings of the replacement capacitors must be the same.

Using a lower capacitance (μF) is used in the starting capacitor, the same problem occurs with the motor overheating as higher current is pushed through the windings and can damage the motor.

If a wrong capacitance is used for the operating capacitor, the magnetic field around the motor will be erratic and the motor will resonate at full load. This frequency makes the motor noisier, less efficient, and more susceptible to overheating.

The replacement capacitor shall have a voltage rating equal to or better than the installed capacitor.

340V motor run capacitors can be used for 370V motor drive capacitors.

A370V motor running capacitors cannot be used in place of 440V motor running capacitors.

The A370/440 V rating means that the same capacitor can be used for both voltages.

Replacement capacitors should be similar in physical size. The new capacitor should fit snugly into the chassis. Small diameters and lengths can cause capacitors to slip and shorten housing tabs.

Name the alternate capacitor. Label the replacement capacitors with a paint or marker and tape (Fig. 13). This makes it easy to keep track of what has been tested and replaced and to identify ongoing problems with this motor.

Safety Instructions

Always disconnect electrical equipment prior to inspection and maintenance.

Always consult an electrician when working with an electrical system.

By design, kinetic capacitors store electrical energy. This energy is sufficient to cause an electric shock to an individual and cause damage. Other injuries, such as head injuries, may occur from falling backwards.

Always read the manual and follow the technical and safety instructions when performing maintenance work on the electrical system and its components.

Always wear personal protective equipment (PPE).

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