Test the motor First stop the motor and remove the electric power cable from the motor. Set your multimeter to DCV mode. A multimeter is identical to an ohmmeter, and both will suffice for this test. Connect your tool and select a voltage from the DCV (direct current voltage) area. Choose a voltage that is similar to the voltage used by your tool.
You may adjust the DCV to 20 for most electric motors.
Test the motor
Using Multimeter to test the motor
Use the “Resistance or Ohms” setting for an ohmmeter.
Make sure the numbers are set to 0 when you turn on the tool. If the display does not read 0, press the probes together to zero it out. If you have a digital multimeter, it will immediately zero out.
2Connect the probes to the motor’s positive and negative sides. Make sure your electric motor is turned off and disconnected. Electric motors come in a variety of configurations: some have positive and negative probes, while others include a grounding probe and motor leads. Connect your tool’s two wires to your electric motor in one of the following ways:
Locate a ground screw (typically a green, hex head type) or any metal component of the frame (scrape away paint if necessary to get excellent contact with metal) and push a test probe to this place, one at a time.
Find the red (positive) and black (negative) wires. Connect one probe from your tool to each wire.
3Keep an eye on the display for a resistance value. Ideally, the meter should scarcely shift away from the greatest resistance indication while still displaying numbers indicating resistance. Make sure your hands are not contacting the metal probe tips, since this can result in an erroneous readout.[3]
If the numbers do not move at all, your electric motor most likely has an electrical fault. Continue reading to figure out what’s wrong.
It varies on the type of motor being tested, although most motors exhibit negligible resistance.
4Examine the windings for any short circuits to the frame. Most home appliance motors with a shorted winding will not operate and will most likely immediately open the fuse or trip the circuit breaker (600 volt systems are “ungrounded,” therefore a 600 volt motor with a shorted winding may run and not trip a fuse or circuit breaker).
5Make sure the windings aren’t open or blown. Many basic ‘across the line’ single-phase and three-phase motors (used in home appliances and industrial, respectively) may be tested easily by setting the ohm meter range to the lowest provided (R X 1), zeroing the metre again and measuring the resistance between the motor’s leads. In this situation, review the motor’s wiring diagram to ensure that the metre is measuring across each winding.
Expect to observe a very low resistance number in ohms. Resistance levels in the single digits are predicted. Make sure your hands are not contacting the metal probe tips, since this can result in an erroneous readout. numbers over this suggest a possible issue, whereas numbers substantially above this indicate that the winding has failed to open. A motor with a high resistance will not run – or will not run with speed control (as occurs when the winding of a three-phase motor opens while running).
Checking the Bearings
Examine both ends of the motor.
1Bearing failures are the root cause of many electric motor failures. Bearings enable the shaft or rotor assembly to rotate freely and smoothly within the frame. Bearings are situated at both ends of the motor and are referred to as “bell housings” or “end bells” by some.
Bearings come in a variety of shapes and sizes. Brass sleeve bearings and steel ball bearings are two prominent varieties. Many have lubrication fittings, while others are permanently lubricated or “maintenance free.”
Rotate the shaft or rotor.
2Place the motor on a firm surface and place one hand on the top of the motor while spinning the shaft/rotor with the other hand to do a quick inspection of the bearings. Keep a close eye, feel, and ear out for any signs of rubbing, scraping, or unevenness in the spinning rotor. The rotor should spin easily and silently.
Try lubricating the bearings if they are not rotating freely. They might be clogged and unable to rotate.
Push and drag the shaft into and out of the frame.
3A limited amount of movement in and out is permissible (most domestic fractional horsepower kinds should be less than 1/8″ or so), but the closer to “none” the preferable. When a motor with bearing difficulties is operated, it will be noisy, overheat the bearings, and perhaps fail catastrophically.[9] Lubricate the bearings if they are stuck or jammed.
Troubleshooting Additional Potential Issues
1Check the run or start capacitor.
A metal cover on the outside of the motor protects most capacitors from damage. Remove the lid to gain access to the capacitor, then inspect it for leaking oil, container bulges, container holes, or smoke residue.
Alternatively, use an ohmmeter to examine the capacitor’s electrical resistance. Place the test probes on the capacitor terminals and observe the resistance as it rises progressively. If it remains shorted or does not rise, the capacitor is most likely faulty and must be replaced.
2Examine the motor’s rear bell housing.
Centrifugal switches are used in some motors to switch the start / run capacitor (or other windings) “in” and “out” of the circuit at a specified RPM. Check that the switch contacts are not welded shut or clogged with dirt and oil, which might hinder a good connection. Check with a screwdriver to determine whether the switch mechanism and any springs can be freely manipulated.
3Take a lock at the fan.
A “TEFC” motor is a “Totally Enclosed, Fan Cooled” motor. On the rear of the motor, the fan blades are hidden by a metal guard. Ascertain that it is firmly secured to the frame and that it is not blocked with dirt or other debris. The rear metal guard apertures must allow complete and unobstructed air circulation; otherwise, the motor would overheat and finally fail.
4Select the appropriate motor for the operating circumstances.
Check that drip-proof motors are not exposed to any water or moisture, and that open motors are not exposed to any water or moisture.
- Drip-proof motors can be put in damp or wet areas as long as they are installed such that water (and other liquids) cannot enter owing to gravity and are not subjected to a stream of water (or other liquids) directed at or in it.
- As the name says, open motors are entirely open. The motor’s ends have quite big apertures, and the windings in the stator windings are clearly visible. These holes should not be covered or limited in these motors, and they should not be put in damp, unclean, or dusty environments.
- TEFC motors, on the other hand, may be utilized in all of the above regions but must not be submerged unless particularly developed for the purpose.
5Examine the motor’s outside.
If the motor has any of the following defects on the exterior, these might be difficulties that decrease the motor’s life due to past overloading, incorrect use, or both. Keep an eye out for:
Mounting holes or feet that are broken
Darkened paint in the centre of the engine (showing overheating)
Evidence of dirt and other foreign materials being drawn into the motor windings through housing apertures
