Single-phase motors (in household appliances, pumps, machine tools) have their own starting specifications. Ifa single-phase motor hums but does not startthe cause is usually the starting circuit. Let's figure it out.
How a single-phase motor starts
Unlike a three-phase motor, a single-phase motor itself does not create torque when starting. To start, a starting winding and a capacitor are used, which create a phase shift. If this circuit is faulty, the engine only hums.
Main causes
- A faulty capacitor is the most common cause. Lost capacity or broken.
- Breakage of the starting winding.
- Faulty centrifugal switch(in engines with a starting winding).
- Seizing ofshaft or bearings.
How check
| Check | How |
|---|---|
| Capacitor | Measure the capacitance, compare with the nominal |
| Freedom of the shaft | Turn by hand |
| Windings | Resistance of working and starting |
| Starting with | Turn the shaft when starting - if it starts, it’s in the starting circuit |
Attention: the “twist” check is performed carefully and with knowledge of safety precautions. Most often, replacing the capacitor solves the problem. If the winding breaks, rewind is needed. diagnostics will show the exact cause.
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