How can a multimeter be used to simply and quickly detect whether an electric motor is in good condition or faulty?
Using a multimeter to simply measure the condition of an electric motor is a common method we use in our daily work. There are mainly two ways to measure the condition of a motor with a multimeter: using the resistance range and the current range. Now, let me talk about how to simply and quickly detect whether a motor is in good condition or not with a multimeter.
The most common method I use when checking with a multimeter is to disconnect the connections between the three - phase windings before the inspection, so that the windings of the three - phase motor are not connected to each other. Then, set the multimeter to the ohm range of RX10K. Connect one probe of the multimeter to one end of the winding and the other probe to the motor's housing. At this time, we can observe 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 grounding fault between this phase winding of the motor and the motor housing. If the measured resistance value is very large, it means there is no grounding fault.
We can also use the resistance range of the multimeter to measure the three independent windings respectively. First, we need to know the normal resistance values of the three windings. During the measurement, if the resistance values of the three windings are the same, it indicates that the windings are normal. If there are differences in the resistance values of the three independent windings, it means the motor is abnormal. Then, we can use a megger to measure the insulation resistance values between the three windings of the motor. The resistance values between each pair of them are generally between 0.5 megohms and 1 megohm, which should be considered normal. Finally, use the megger to measure the insulation conditions of the three windings to the motor housing (ground) respectively. Normally, the resistance value should be around 0.5 megohms to 1 megohm, which is considered normal.
Another measurement method using a multimeter is to use the current range, but this method can only be used for small three - phase motors. For example, for a three - phase asynchronous motor with a power below 4KW, its rated current during operation is about 8.8 amperes. The maximum current measurement value of a general multimeter is 10A. If we want to measure a motor with a relatively large power, we can use a special clamp - on ammeter. The main purpose of this method is to measure whether the three - phase currents of the motor are balanced. If the currents are unbalanced, it means that the motor also has a fault.
