Measure the resistance between the motor terminals and compare it with a known good motor (or the datasheet). If the coils have melted, they will have shorted and you'll see a lower resistance. Or they will have broken altogether, and you'll read infinite resistance.
Some manufacturers estimate 30,000 hours, while others state 40,000 hours. Some will say “it depends.” One thing is clear—a motor should last much longer with a conscientious motor systems maintenance plan than without one. Motor life can range from less than two years to several decades under particular circumstances.
Winding insulation breakdown and bearing wear are the two most common causes of motor failure, but those conditions arise for many different reasons.
Overheating is the most common cause of motor failure. Overheating damages the insulation protecting the motor windings allowing it to "short out." A 20-degree temperature increase beyond the rated temperature rise can reduce the insulation's effectiveness by 50%.
If it's relatively new and has no other signs of wear and tear, a repair may extend its life substantially. But if the motor is old and showing multiple signs of wear, such as overheating, strange noises, or frequent breakdowns, it might be time to replace it.
Improper lubrication, inappropriate mechanical loads, heat, contamination and shaft currents are all the usual suspects when it comes to bearing problems. Get the bearing failure checklist. A winding failure—which is often caused by a breakdown of the winding's insulation—will cause a short in the motor.
When your electric motor fails to start, begin by checking the motor and the load are turning freely. Ensure the load does not require more power than the motor can deliver. If the motor is being operated for the first time, ensure the wiring is correct. Next, check the motor circuit.
Newly assembled motor does not work: rotor does not spin. Rotor is in a "dead spot" – the magnet is outside of reed switch working range. This usually occurs with 2 magnet rotors.
Measure the resistance between each motor winding using a multimeter. Compare the measured values with the motor's specifications or reference values provided by the manufacturer. Abnormally low resistance readings may indicate a short circuit.
Theoretically, an electric motor can be repaired indefinitely, but practically there is a limit. That limit exists when the price to repair exceeds the price of new or a non-quality vendor has repaired it so many times that you no longer have faith it will run as intended.
One of the most common performance issues in electric motors is overheating. Experts suggest that an 18°F (10°C) degree increase in motor winding temperature can directly affect the insulation of the component and reduce its lifespan by 50%.
Use a multimeter or an ohmmeter to test the voltage of the electric motor. If there is no resistance or the resistance is uneven, the motor is likely faulty. Check the bearings to make sure they can spin freely. If they can't, lubricate them.
Belts can wear away with heavy use or excess heat. Excessive vibration can cause belts to shift and possibly rub up against another part causing additional wear and tear. Inspecting the belts on an industrial electric motor should be a standard task in any electric motor preventive maintenance program.
Restricted Ventilation: Covering the motor's enclosure can result in the motor to overheat. Improper Lubrication: Not only can this result in damaged bearings but can also throw grease into windings. Moisture: Condensation can cause rust within an enclosed motor.
Insulation Degradation
Insulation degradation happens when the insulating materials in the motor break down, which can lead to short circuits and failures. This can be caused by high temperatures, moisture, chemical exposure, or mechanical damage.
Winding insulation breakdown and bearing wear are the two most common causes of motor failure, but those conditions arise for many different reasons.
The reasons causing a motor to overheat are varied. These include improper wiring, loose connections, or undersized line sizes causing a voltage drop at the motor. In other instances, slippage from loose belts transfers heat to the motor through the shaft.
Inspect the Motor Windings With a Multimeter
First and foremost, you're going to need a multimeter to test the windings. To begin, set the multimeter to read ohms and then test the motor's wires and terminal. You should test the windings for a “short to ground” in the circuit and open or shorts in the windings.