How to judge the quality of AC three-phase, AC single-phase and DC motors?

1. How to detect the quality of AC three-phase motor?

1. Use a megohmmeter (a 500V megohmmeter will do). If the insulation resistance of the wires on the three terminals to the motor housing is above 0.5M ohms, it means there is no short circuit to ground.

2. Use a multimeter to measure the resistance between the three phases A/B/C. Are they equal? ​​They should be about the same. If they are too different, they can still rotate, but they won't last long. Remember that the larger the motor, the smaller the resistance! However, the three phases cannot be 0 ohms, unless you have a very large motor, such as a motor of more than 50KW! Remember that the resistance of the six terminals of a speed-controlled motor may be different!

3. Check the bearings and fans. If the motor is entangled, replace them all! Because sometimes the bearings will lock and burn the motor!

4. The no-load current of the motor is generally 10% to 50% of the rated current. Sometimes the motor idling current is zero!

5. When the motor is running at rated current, it is running at full load, and the output power is basically 100%. If the running current is small, it means that the motor output power is reduced, and it is running at light load.

2. How to detect the quality of AC single-phase motor?

Use a 500V megohmmeter to measure the insulation resistance between the motor winding and the casing. It should not be less than 0.5 megohms. Use a multimeter to measure the leads of the winding. If there are no broken wires, if all of the above meet the requirements, the motor is good.

It is more convenient to use a pointer multimeter to check the quality of capacitors (there are also digital meters with capacitance ranges that can be used for direct measurement).

Set the multimeter to 1K or 10K resistance range, measure the two leads of the capacitor, the needle quickly deflects to the right and then slowly returns to the left side, the capacitor is good, always deflects to the right side, indicating that the capacitor is broken, the needle does not move, the capacitor is broken or has no capacity. This method can only be used to judge whether the capacitor is good or bad.

3. Is the DC motor good or bad?

First check whether there is any broken wire and measure whether the resistance is normal.

If it is a brushed DC motor, you can let the rotor rotate and use a multimeter to measure whether the output DC current is normal.

If it is a brushless DC motor with three-phase output, the rotor can be rotated and a multimeter can be used to measure whether the output alternating voltage is normal.

The output voltage is proportional to the speed.