How to Test a Single-Phase Motor

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Your washing machine, your electric dryer, your refrigerator, your generator -- all these appliances work by way of a motor. And in most cases the motor found in these devices is known as a single-phase motor. While a single-phase motor is normally resilient and can operate unhindered for decades, there will come a time when it will break down and cause problems. However, before springing for a replacement, you may want to conduct some simple tests to see if the motor can still be repaired. This will save you a whole lot of time and money.


Step 1

Testing a single-phase motor will require some preparation. For starters, you will need to wear safety gear. A pair of safety glasses and work gloves will do nicely, since dealing with a motor can accidentally send shocks to your body. And, since the voltage is considered high, it will be wise to take the necessary precautions.

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Step 2

Remove the motor's wire cover. The cover will be fastened securely by screws. Locate the two or four screws, depending on the motor model, and unscrew them with the slotted screwdriver. Lift the cover gently to expose the wire leads. There should be two wire leads for a single-phase motor. These wires will be connected to the power supply of the device or appliance. While the wire leads are exposed, check the voltage rating of the motor. There should be a label indicating the voltage range.


Step 3

Disconnect the wires. In order to effectively test the motor, you will be required to disconnect it from the power supply. Use a pair of pliers to detach both wires. Each wire should have a plastic end going to the power supply. Simply pull it out.

Step 4

Test the lead. This step will require a volt-ohm tester. Your tester will have two wires with lead tips. One of the tips should touch the motor's case while the other touches one of the exposed wire leads. Read the results on the tester, then repeat the same procedure with the other exposed wire lead. If both tests result in 0 ohms, the motor does not have any major problems and can still be used. On the other hand, if the results indicate a charge, it could mean that there is a short or that the motor has broken down due to worn-out bearings or extreme heat.


Step 5

Test the capacitor. Unlike three-phase motors, a single-phase motor uses a capacitor to function. If the lead tests resulted in normal readings, the next step will be to test the capacitor. Locate the capacitor and remove it. It is important that you wear gloves at this point, as the capacitor is charged with high voltage, which will automatically discharge should you accidentally touch its lead parts.


At this point, switch your tester to read volts. Place one tip on one of the two leads. The other tip goes on the other lead. If the voltage reading is above 0, the capacitor is still charged and there is nothing wrong with it. However, if it reads 0, then the capacitor has died out and needs replacement.



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