How to use a multimeter to easily and quickly detect whether a motor is good or bad
Using a multimeter to simply measure the quality of a motor is a commonly used method in our daily work. Using a multimeter to measure the quality of a motor mainly uses two methods: electrical barrier measurement and current barrier measurement. Let me talk about how to use a multimeter quickly and easily. To detect whether the motor is good or bad.
The most common way I use a multimeter to check is to disconnect the connecting wires between the three-phase windings before checking, so that the windings of the three-phase motor are not connected to each other, and then adjust the multimeter's gear to the RX10K ohm gear. Then connect one test lead of the multimeter to one end of the winding, and connect the other test lead to the motor casing. At this time, we can look at the resistance value indicated by the multimeter. If the resistance value indicated by the multimeter is very small, or even zero, it means that there is a ground fault between the phase winding of the motor and the motor shell. If the measured resistor value is very large, it means there is no ground fault.
We can also use a multimeter to measure the three independent windings separately. We first find out the normal resistance values of the three windings. If the resistance values of the three windings are the same during measurement, it means that the windings are normal. If the resistance values of the three independent windings are different, it means that the motor is abnormal. Then you can use a megger (megohmmeter) to measure the insulation resistance value between the three windings of the motor. The resistance value between them is generally between 0.5 megohm and 1 megohm, which should be a normal value. Finally, use a megger to measure the insulation of the three windings to the chassis (to ground). The normal resistance value should be around 0.5 megohm to 1 megohm, which is normal.
Another way to measure with a multimeter is to use the current block of the multimeter, but it can only be used on small three-phase motors, such as three-phase asynchronous motors below 4KW. Its rated current when working is 8.8 amps. of current. The maximum current measurement value of our general multimeter is 10A. If you want to measure a motor with a relatively large power, you can use a special clamp ammeter to measure it. We use this method mainly to measure whether the three-phase current of the motor is balanced. If the current is unbalanced, it means that the motor is also faulty.
In fact, in many cases, we can judge the basic condition of the motor without using a multimeter. For example, we can roughly judge the basic fault of the motor by "looking", "smelling" and "touching", because when the motor fails, we It can be seen from its operation that the motor's speed suddenly slows down, there is abnormal noise, the surface temperature of the motor is too high, the motor casing is electrified, etc., all are caused by different faults in the motor.
