Under normal circumstances, even if a frequency inverter is faulty, it will display a corresponding fault indication after being powered on. So, what should we do to check and repair a frequency inverter that does not respond after being powered on?
Troubleshooting methods for inverters that do not respond after power-on
First, check if there is a problem with the power switch's power supply. If you are unsure, you can perform a professional power supply test. If it is a power supply problem, simply replace the power switch with a different one!
2. If the power supply test is normal, we will then perform a static test. Set the multimeter to the resistance x10 range. Connect the red probe to the P terminal of the inverter, and the black probe to R, S, and T in sequence. At this point, there will be a resistance of approximately tens of ohms, which is basically balanced. When the black probe is connected to the P terminal, and the red probe is connected to R, S, and T in sequence, there will be a resistance close to infinity. Then connect the red probe to the N terminal and repeat the above process. If the result is the same, the static test is normal.
3. If the static test of the frequency converter is normal, we will then perform a dynamic test, i.e., an on-machine test. Start the frequency converter under no-load (without connecting the motor) conditions and test the U, V, and W three-phase output voltage values. If there is a phase loss or three-phase imbalance, the module or drive board is faulty. Under normal output voltage (no phase loss, three-phase balance), perform a load test. It is best to perform a full-load test.
Having completed the above steps, we can basically determine the specific reason why the inverter is unresponsive after being powered on. At this point, we can then address the problem specifically. It is recommended that the above steps be handled by a professional inverter repair technician to avoid damaging the inverter.
Causes and solutions for inverter power-on no display fault
The fault of no display when the frequency converter is powered on usually occurs in three modules: first, the contactor; second, the control panel of the frequency converter; and third, the power supply module that supplies power to the control panel.
Fault detection 1: When the frequency converter is powered on, there should be a sound of the contactor engaging at the moment of power-on. If there is no such sound, the contactor may be faulty.
Solution: Replace with a new contactor.
Fault Detection 2: If the contactor is not the problem, check the power module. If the high-voltage power supply LED on the inverter is lit, it indicates that the high-voltage DC power supply is normal. If there is no DC voltage in the low-voltage DC power supply, this indicates the switching power supply is not working. A non-working switching power supply is equivalent to the switching transistor not working. The lack of DC voltage indicates a damaged or open circuit in the step-down resistor connecting the high-voltage DC terminal and the primary winding of the pulse transformer, resulting in the high-voltage DC power not being applied to the primary winding of the pulse transformer. With the switching power supply failing to work, the entire inverter receives no low-voltage DC power, resulting in a no-display fault.
Solution: Replace the step-down resistor.
Fault Detection 3: The high-voltage LED indicator on the inverter is lit, and the LED indicator on the main control board is also lit, indicating that the inverter switching power supply is normal and the DC voltage display on the main board and the main control board is normal. Then use an oscilloscope to check the main control board to see if there is an output signal. If there is no output signal, then one of the chips, HC245, is damaged.
Solution: Replace the HC245 chip.
Disconnect the power cord and check for any missing phases or open circuits in the power supply. If the power supply is normal, power it on again and check if there is voltage at the DC side terminals P and N of the inverter's intermediate circuit. If the above checks are normal, then the inverter's internal switching power supply is damaged.
Power-on tripping or sparking at the inverter's main power supply terminals:
Disconnect the power cord and check if the inverter input terminals are short-circuited. Also check if the DC side terminals P and N of the inverter's intermediate circuit are short-circuited. Possible causes include a damaged rectifier or a short circuit in the intermediate circuit.
No output upon startup (motor does not start):
Disconnect the output motor wire, restart the inverter, and observe the input frequency displayed on the inverter panel. Simultaneously, measure the AC output terminals. Possible causes include incorrect inverter startup parameter settings or incorrect wiring of the running terminals, damage to the inverter section, or the motor not being properly connected to the inverter.
