Measuring no-load current is a simple but informative diagnostic method. It can be used to judge the condition of the winding, rotor and magnetic system. Let's look at what it shows.
What is no-load current
This is the current that the motor consumes without load on the shaft. It is used mainly to create a magnetic field. In a working engine, the no-load current is a certain fraction of the rated current (usually 20–40% depending on the power).
How it is measured
- The engine is started without load (without connection to the mechanism).
- The current in each phase is measured using a clamp meter.
- The values are compared by phase and with the expected value.
What is it about? they say deviations
| Result | Possible cause |
|---|---|
| The current is the same and normal | The motor is OK |
| Increased current | Problems of the magnetic system, turn short circuit |
| Distortion by phase | Interturn short circuit, break |
| Current ripple | Breakage of rotor rods |
When used
The no-load current is checked during diagnostics and always after rewind - as quality control. Increased or uneven current indicates a defect in the winding or rotor.
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