When a motor failed to start, the first thing one should instantly check is the incoming power supply to that motor. If the supply voltage is within limit, then there is a possible scenario of motor burning out or other vfd, wiring and winding problems. It’s so difficult to say something about motors apparently because they show no damage from their outside body.
For troubleshooting a failed motor first of all disconnect power from it. Because for motor check out there is no need of power to motor. You’ll need a trusted brand ohm meter to test the motor. Now follow the easy steps below for learning “how to test a motor with multimeter”.
1. Physical checkup of motor
We always advise electricians or electronic technicians and hobbyists to examine electronic devices apparently before going to further testing and repairing. Because sometimes a small fix of unusual physical issues can sort out the problem.
- Thoroughly check motor, there should be no dirt and debris especially inside of motor winding area.
- Check motor’s rotor if there is loosing or the bearing has left its place slightly. Also bearing should move freely when you try to spin it.
- Touch motor body, if it’s too hot probably winding has been shorted.
- Open Ac motor connection box and check all wires, there should be no sign or spark, and see if wires are connected firmly with junction box.
- check ground connection.
2. How to test Motor with Multimeter
- Set multimeter on resistance testing, and place probes into their respective jacks.
- Set your meter on highest range of ohms, if it’s not an auto range multimeter.
- Touch meter probes with each other to calibrate the meter on zero value.
- Now we have to check resistance of motor winding, for that carefully see motor winding diagram because we have to check resistance values across every winding.
- Now connect red lead of meter with anyone of terminals like with T1 and black lead with the ground.
- It should give an infinite value of resistance across each terminal with ground if motor winding is fine.
- If you get a zero or near to zero ohm value then there may be some problem with winding or power wires.
- Now if there is a zero value, you have to isolate power cables to check whether there is an issue with winding or cables?
- After that disconnect power cables which are connected with motor and now check resistance between motor terminals and ground, it also should give an infinite ohms value.
3. How to test for a short and open in motor winding
- keep multimeter on resistance checking mode.
- For testing ac motor winding we have to remove power cables from it.
- Now test terminals one by one with one another. Connect meter with T1, T2 then T1 to T3, and T2 to T3 and check ohm values.
- For a stable and fine winding, the meter should show an ohm value between 0.7 to 1.8 ohms. As a rough idea, any reading between 0.4 to 2.2 is acceptable.
- If you get an infinite resistance or a significantly higher value than 2.2 ohms then it indicates that there is an open or broken connection between winding.
- And if you receive a zero or near to zero results then your motor has a short, in simple words either one or two winding have been burnt.
4. Some other Motor inspections
If motor windings are fine you may also check some other factors which can play a role in malfunctioning of motor.
- Some motors have a capacitor for starting purposes, do a physical check up of that capacitor. Remove capacitor cover and look for any sign of leakage, spark, swelling, and unusual smell.
- Check the fan of motor by removing nut and bolts of its cover. Fan should move freely with rotor speed, there should be no breakage in fans. If fan is not flowing well motor will overheat and could also burn out.
- Make sure that, there are no metal type things or wires touching the motor body when it’s in running condition.
- Also, look for oil and grease leakage on the motor body.