Is it possible to measure the motor with a multimeter or not?
We can know that the multimeter can measure AC voltage, DC voltage, AC current, DC current, as well as resistance and capacitance, buzzer file, secondary tube, etc., and there is also an intelligent anti-burn protection design, automatic shutdown, etc., it can be said that the function is still quite powerful. For an ordinary electrician, completely enough.
Then the multimeter in the end can not measure the motor is good or bad? And how to measure?
I think this has to be viewed in two ways. If it is a short circuit between the coils, turn-to-turn short circuit, broken circuit, these can be measured with a multimeter. If it is a short circuit to ground, leakage to ground, this aspect of the insulation resistance value should be used megohmmeter (insulation resistance meter, shaking table).
The following is a brief description of the use of a multimeter to measure short circuits between motor coils and coils, as well as short circuits and breaks between turns of coils.
Motors come in all sizes, but three-phase motors are made up of three windings. Measuring the resistance of the three-phase windings is essential to determine if the motor is faulty. The resistance value of the three-phase winding varies according to the power size of the motor, but the difference in their resistance values will not be very large, usually between 2 and 5 ohms.
Usually three-phase motors are 6 terminals, but some of the smaller power, the manufacturer has been knotted inside the motor star or angle, in the junction box is only three terminals. The detection method of this motor and the six terminal detection method is the same, but the coil turn-to-turn short circuit, we can not detect the ordinary electrician.
Before we measure it, we first have to disconnect the power supply and remove the connecting tabs. Assume that the top three wires are the first end and the bottom three wires are the last end. It's not convenient to type letters for the first and last ends, so I'll name the first end 1,3,5 and the last end 2,4,6.
Because we don't know what the resistance between the three-phase windings is, let's start by hitting the multimeter to one of the resistance stops, and then finally find the right stop and do an exact comparison.
Find the appropriate gear, respectively, measure the resistance between the first three-phase winding, if the difference between the three-phase winding resistance is not large, within a reasonable range, we believe that the resistance between the three-phase winding is normal. Really uneasy, we can be measured at the end of the tail end again, do a comparison, this way can ensure that nothing is wrong.
Problems between the three-phase windings are easier to solve. The turn-to-turn fault judgement of the coil is relatively troublesome.
Let's start with a turn-to-turn short circuit. Turn-to-turn short circuit is the phenomenon of motor local heating, three-phase current imbalance, measured with a clamp meter, short-circuit has always been much higher current. With a multimeter to measure the resistance of the three-phase coil at the end of the first and last, the short-circuited phase to be much smaller.
If the turns are disconnected, the resistance of the first and last ends of the coil windings should be infinite or very large.
If the coil is shorted to ground or is leaking, a megohmmeter is required. Because the voltage level of the multimeter is too low, there is no way to measure accurate data.
Measurement of low-voltage equipment or wiring, we choose 500 megohmmeter can be.
The megohmmeter is also called a rocking meter because it is a hand-cranked DC generator.
A megohmmeter is also called an insulation resistance meter and is specifically designed to measure insulation resistance above the megohm level.
Usually the industry standard is to reach 0.5 megohm insulation resistance to ground is normal.
The operation is very simple, we put the insulation resistance meter flat and stable, and debugging calibration, can be measured.
The megohmmeter L terminal connected to the motor winding resistance, the E terminal connected to the motor shell, respectively, to measure the motor 6 wires on the motor shell resistance, insulation resistance greater than or equal to 0.5 megohm for normal, less than 0.5 megohm is considered to be leakage, resistance value is very small, is a short circuit.
