How to Use a Multimeter to Detect the Condition of an Inverter
It should be noted that for personal safety, the machine must be powered off, and the input power cables R, S, T and the output cables U, V, W of the frequency converter should be removed before operation! First, set the multimeter to the "diode" gear, and then use the red and black test leads of the multimeter to detect according to the following steps:
Touch the negative pole P(+) of the DC bus with the black test lead, and touch R, S, T in turn with the red test lead, and record the display value on the multimeter. Then touch N(-) with the red test lead, and touch R, S, T in turn with the black test lead, 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.
Touch the negative pole P(+) of the DC bus with the red test lead, and touch U, V, W in turn with the black test lead, and record the display value on the multimeter. Then touch N(-) with the black test lead, and touch U, V, W in turn with the red test lead, 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 phenomena are no output or fault reporting.
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 process and can remain basically unchanged, it is a good frequency converter.
The lowest frequency can be calculated as follows: (synchronous speed - rated speed) × 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.
Touch the negative pole P(+) of the DC bus with the red test lead, and touch U, V, W in turn with the black test lead, and record the display value on the multimeter. Then touch N(-) with the black test lead, and touch U, V, W in turn with the red test lead, 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 phenomena are no output or fault reporting.
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 process and can remain basically unchanged, it is a good frequency converter.
The lowest frequency can be calculated as follows: (synchronous speed - rated speed) × 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.
