How to test a motor for burns with a multimeter
Multimeter to measure whether the motor burned out, first of all, to find out whether the pump motor is a three-phase motor or single-phase motor, the measurement method is different.
1, three-phase motor measurement method
The multimeter will hit the resistance 200 ohm block. Measure the three-phase resistance, general 750-watt motor resistance value of about 20 ohms, 4000-watt motor resistance value of 3 to 5 ohms, according to the different resistance value of the motor is slightly different. If the three-phase resistance value is the same, the difference is not large, you can initially judge the three-phase winding is basically normal, there is no turn-to-turn short circuit.
Then, the junction box three-phase short-circuit piece apart, the multimeter to 20M ohm block, measuring the three-phase and three-phase insulation resistance value of the shell, the resistance value should be infinite. Because the power supply battery of the multimeter is nine volts, only a preliminary judgement of its insulation resistance. The size of the specific insulation resistance needs to be measured with a 500-volt shaking table, the insulation resistance value of more than 5M is normal.
The above is the judgement of the motor under normal circumstances. If the three-phase resistance value difference is large, resistance value of zero or no resistance value, can be basically determined that the motor has burned or phase break, need to dismantle the motor for further inspection. If the insulation resistance is small, to judge whether it is a short circuit or moisture.
2, single-phase motor measurement
Single-phase motor and three-phase motor measurement is almost the same, single-phase motor only the main winding and secondary winding, measurement of the main winding U1 and U2 and secondary winding Z1 and Z2 resistance. Generally, the resistance value of the secondary winding is greater than that of the main winding, but there are also the same resistance value of the main winding and the secondary winding.
If the resistance value is normal, the connection piece will be removed. Measure star main winding and secondary winding between the phase of the insulation resistance value and the insulation resistance value of the shell. Measurement method is the same as the three-phase motor.
Precautions
1,Before disassembling, blow the motor surface dust with compressed air and wipe the surface dirt clean.
2,Choose the working place of motor disassembling and clean up the site environment.
3,Familiarise yourself with the structural characteristics of the motor and the technical requirements for overhaul.
4,Prepare the tools (including special tools) and equipment needed for disintegration.
5, in order to further understand the defects in the operation of the motor, when possible, can be disassembled before doing a check test. To this end, the motor will be loaded with a test spin, a detailed inspection of all parts of the motor temperature, sound, vibration, etc., and test the voltage, current, speed, etc., and then disconnect the load, a separate no-load inspection test, measured no-load current and no-load loss, make a good record.
6,Cut off the power supply, remove the external wiring of the motor, make a record.
