How to detect the good and bad of motor simply and quickly by multimeter
Simply measuring the quality of the motor with a multimeter is a common method in our work. Measuring the quality of the motor with a multimeter mainly uses two methods: electric blocking measurement and current blocking measurement. Let me talk about how to detect the quality of the motor simply and quickly with a multimeter.
The most common way to check with a multimeter 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, then adjust the gear of the multimeter to the ohm gear of RX10K, and then connect one probe of the multimeter with one end of the winding and the other probe with the motor shell. At this time, we can look at the resistance indicated by the multimeter. If the resistance indicated by the multimeter is very small or even zero, it means that there is a grounding fault between this phase winding of the motor and the motor shell. If the measured resistance is very large, there is no ground fault.
We can also use the multimeter to measure the three independent windings separately. Let's first find out the normal resistance values of the three windings. When measuring, if the resistance values of the three windings are the same, 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 measure the insulation resistance between the three windings of the motor with a shaking table (megger). The resistance between them is generally between 0.5 megohm and 1 megohm, which should be normal. Finally, measure the insulation of the three windings to the casing (ground) with a shaking table. The normal resistance should be about 0.5 megohm to 1 megohm, which should be normal.
The other method is to use multimeter to measure the current, but it can only be used in small three-phase motors, such as three-phase asynchronous motors below 4KW, whose rated current is 8.8 amps when working. However, the maximum current measurement value of our general multimeter is 10A. If you want to measure a motor with high power, you can use a special clamp ammeter to measure it. We mainly use this method 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 multimeter. For example, we can also roughly judge the basic faults of the motor by "seeing", "smelling" and "touching", because we can see from its operation when the motor fails, such as the sudden slow speed of the motor, abnormal noise, high surface temperature of the motor, and electrification of the motor shell, which are all caused by different faults of the motor.
