How to use a multimeter to detect the quality of an inverter?
It should be noted that for personal safety, it is necessary to ensure that the machine is powered off and the input power wires R, S, T and the output wires U, V, W of the frequency converter are removed before operation! First, set the multimeter to the "diode" gear, and then use the red test lead and the black test lead of the multimeter to detect according to the following steps:
The black test lead touches the negative pole P(+) of the DC bus, and the red test lead touches R, S, T in turn, and record the display value on the multimeter. Then the red test lead touches N(-), and the black test lead touches R, S, T in turn, and record the display value of the multimeter. If the six display values are basically balanced, it indicates that there is no problem with the diode rectification or the soft-start resistor of the frequency converter. Otherwise, the rectifier module or the soft-start resistor at the corresponding position is damaged, and the phenomenon is no display.
The red test lead touches the negative pole P(+) of the DC bus, and the black test lead touches U, V, W in turn, and record the display value on the multimeter. Then the black test lead touches N(-), and the red test lead touches U, V, W in turn, and record the display value of the multimeter. If the six display values are basically balanced, it indicates that there is no problem with the IGBT inverter module of the frequency converter. Otherwise, the IGBT inverter module at the corresponding position is damaged, and the phenomenon is no output or a fault alarm.
Use the frequency converter to drive an asynchronous motor with a matching power to run no-load on-site, and adjust the frequency f, starting from 50Hz and decreasing to the lowest frequency.
During this process, use an ammeter to detect the no-load current of the motor. If the no-load current is stable during the frequency decrease and can remain basically unchanged, it is a good frequency converter.
The lowest frequency can be calculated as (synchronous speed - rated speed) × number of pole pairs p ÷ 60. For example, for a 4-pole motor with a rated speed of 1470 revolutions, the lowest frequency = (1500 - 1470) × 2 ÷ 60 = 1Hz.
There is no problem with the soft-start resistor. Otherwise, the rectifier module or the soft-start resistor at the corresponding position is damaged, and the phenomenon is no display.
The red test lead touches the negative pole P(+) of the DC bus, and the black test lead touches U, V, W in turn, and record the display value on the multimeter. Then the black test lead touches N(-), and the red test lead touches U, V, W in turn, and record the display value of the multimeter. If the six display values are basically balanced, it indicates that there is no problem with the IGBT inverter module of the frequency converter. Otherwise, the IGBT inverter module at the corresponding position is damaged, and the phenomenon is no output or a fault alarm.
Use the frequency converter to drive an asynchronous motor with a matching power to run no-load on-site, and adjust the frequency f, starting from 50Hz and decreasing to the lowest frequency.
During this process, use an ammeter to detect the no-load current of the motor. If the no-load current is stable during the frequency decrease and can remain basically unchanged, it is a good frequency converter.
The lowest frequency can be calculated as (synchronous speed - rated speed) × number of pole pairs p ÷ 60. For example, for a 4-pole motor with a rated speed of 1470 revolutions, the lowest frequency = (1500 - 1470) × 2 ÷ 60 = 1Hz.
Judgment of AC and DC solid-state relays: Generally, next to the input terminal and the output terminal of the DC solid-state relay shell, there are marked with "+" and "-" symbols, and the words "Dc input" and "DC output" are noted. For an AC solid-state relay, only the "+" and "-" symbols are marked on the input terminal, and there is no distinction between positive and negative on the output terminal.
Judgment of the input terminal and the output terminal: For a solid-state relay without identification, use the R×10k gear of the multimeter to distinguish the input terminal and the output terminal by measuring the forward and reverse resistance values of each pin respectively. When the forward resistance of a certain two pins is small and the reverse resistance is infinite, these two pins are the input terminal, and the other two pins are the output terminal. In the measurement with a smaller resistance value, the black test lead is connected to the positive input terminal, and the red test lead is connected to the negative input terminal.
If the forward and reverse resistance values of a certain two pins are both 0, it indicates that the solid-state relay is broken down and damaged. If the forward and reverse resistance values of each pin of the solid-state relay are infinite, it indicates that the solid-state relay is open-circuit damaged.
