If the engine hums, but does not turn over - this is a classic symptom, behind which there are several possible causes. A hum means that power is being supplied to the winding, but the rotor cannot start rotating. Let's look at the reasons in order and what to check first.
Five main reasons
- Phase loss. A three-phase motor has one phase missing - the remaining ones create a hum, but not a starting torque. The most common cause.
- Faulty starting capacitor.Single-phase motors without a running capacitor have no torque.
- Seizing.A damaged bearing or an object caught in the gap mechanically blocks the rotor.
- Overload. The load torque exceeds the starting torque of the motor.
- Interturn short circuit. Part windings are short-circuited, the magnetic field is distorted.
Diagnostic checklist
| What to check | How |
|---|---|
| Presence of all three phases | Multimeter on terminals |
| Freedom of shaft rotation | Rotate the shaft by hand (with de-energized engine) |
| Capacitor | Measure capacitance |
| Winding resistance | Multimeter, compare phases |
If the shaft cannot be turned by hand, the problem is mechanical, most likely in the bearings, and you will need them replacement. If the shaft rotates freely, but the motor hums under voltage, look for an electrical cause.
What not to do
Do not leave a humming motor under voltage for a long time: the winding in this mode quickly overheats, and instead of a simple malfunction you will get a burnt winding and an expensive rewind. Turn off the power immediately after detecting the symptom.
If self-check does not reveal the cause, carry out professional diagnostics - some faults are visible only on the devices. Elektromotors engineers in Tashkent will determine the cause and eliminate it - contact us.