Causes and treatment methods of damage to inverter filter electrolytic capacitors

How to judge whether the filter electrolytic capacitor is damaged? Generally, when the electrolytic capacitor shows the following manifestations, it can be judged as damaged: the appearance exploded, the aluminum shell bulged, the plastic outer sleeve cracked, the electrolyte flowed out, the safety valve opened or pressed out, the top part of the small capacitor cracked, the terminal was severely rusted, the cover was deformed and fell off, all of which indicate that the electrolytic capacitor is damaged.

Use a multimeter to measure the open circuit or short circuit, the capacity is significantly reduced, and the leakage is serious.

The reasons for the damage of electrolytic capacitors are as follows:

(1) The quality of the components themselves is poor (large leakage current, large loss, insufficient withstand voltage, containing impurities such as chloride ions, poor structure, and short life).

(2) The rectifier bridge before filtering is damaged, and AC power directly enters the capacitor.

(3) The voltage divider resistor is damaged, and the uneven voltage division causes a capacitor to break down first, and then other related capacitors also break down.

(4) The capacitor is poorly installed, such as the outer insulation is damaged, the outer shell is connected to an inappropriate potential, the electrical connection and welding are poor, resulting in poor contact, heat and damage.

(5) The heat dissipation environment is not good, causing the capacitor temperature to rise too high, and it will be damaged over time.

When replacing electrolytic capacitors, the following points should be noted:

(1) It is best to choose the same model as the original one when replacing the filter electrolytic capacitor. If the same model cannot be obtained for the time being, the following points must be noted: the withstand voltage, leakage current, capacity, size, polarity, and installation method should be the same.

(2) During the replacement of the electrolytic capacitor, pay attention to the electrical connection (screw connection and welding) to be firm and reliable, the positive and negative poles must not be connected incorrectly, the fixing clamp must be firmly fixed, and the outer insulation sheath of the capacitor must not be damaged. The voltage divider resistor is connected as it is, and the resistance value is measured to make the voltage divider uniform.

(3) For electrolytic capacitors that have been stored for more than one year, the leakage current value should be measured. Before installation, DC should be applied for aging. The DC should be applied at a lower level first. When the leakage current decreases, the voltage should be increased. Finally, at the rated voltage, the leakage current value should not exceed the standard value.

(4) When the replacement capacitor can only be installed in other locations due to the inappropriate size of the capacitor, it must be noted that the busbar from the inverter module to the capacitor cannot be longer than the original busbar, and the area surrounded by the two positive and negative busbars must be as small as possible. It is best to use a twisted pair. This is because the busbar inductance increases when the capacitor connection busbar is extended or the positive and negative busbars surround a large area, causing the pulse overvoltage on the power module to rise, thereby damaging the power module or the overvoltage absorption device.