How to determine whether the inverter filter electrolytic capacitor is damaged?

How to judge whether the filter electrolytic capacitor is damaged? Generally, the electrolytic capacitor can be judged as damaged when the following manifestations occur: the appearance is exploded, the aluminum shell is bulging, the plastic outer sleeve is cracked, the electrolyte has flowed out, the safety valve is opened or pressed out, the top part of the small capacitor is cracked, the terminal is seriously rusted, the cover is deformed and falls 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.

There are several situations in which electrolytic capacitors may be damaged or fail:

1) The internal short circuit or open circuit of the electrolytic capacitor is damaged. The fault phenomenon is the burning of the switch tube and other current limiting components, such as the current limiting resistor in the fuse and the switching power supply. The capacitor is damaged by short circuit or open circuit. When the voltage of the filter capacitor working in high voltage and high current increases for some reason and exceeds its withstand voltage value, it will be broken down and short-circuited and damaged. Or, after the rectifier diode is damaged, the polar electrolytic capacitor is equivalent to working in an AC circuit, and it will heat up and short-circuit and be damaged under a large reverse leakage current. Since the current flowing through the capacitor is very large during a short circuit, the capacitor will generally burst or its sealing plug will bulge out. After the filter capacitor is short-circuited, the fuse or current limiting resistor will burn out, the power supply thick film block or the switch tube, and the rectifier tube will break down. The main manifestation is the "three no" of the whole machine. This kind of fault is common in various types of switching power supplies.

2) Inefficiency or slight leakage caused by reduced electrolytic capacitor capacity. The main reason is that the parameters of the capacitor have changed, but it has not completely failed. It still works to a certain extent, but it does not achieve the desired effect, which causes the existing fault phenomenon. Moreover, this type of fault is difficult to judge and eliminate.

3) Failure, complete leakage or explosion caused by the disappearance of electrolytic capacitor capacity is the most difficult fault to identify and repair after a capacitor failure in a power supply. This is because when measuring capacitor components and testing with a multimeter, everything is normal. However, after the capacitor is installed in the circuit, the capacity of the capacitor disappears completely. This is one of the most difficult soft faults to repair in the circuit, that is, the components cannot withstand voltage and are prone to disappear completely once voltage exists.

The reasons for damage to electrolytic capacitors are as follows:

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

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

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

(4) The capacitor is installed improperly, such as the outer insulation is damaged, the outer casing is connected to an unnecessary potential, the electrical connections and welding points 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 damage over time.

When replacing electrolytic capacitors, there are several things to note:

(1) When replacing the filter electrolytic capacitor, it is best to choose the same model as the original one. If the same model cannot be obtained at the moment, the following points must be noted: the withstand voltage, leakage current, capacity, size, polarity, and installation method should be the same, and the type that can withstand larger ripple current and have a long life should be selected.

(2) When replacing the electrolytic capacitor, make sure that the electrical connection (screw connection and welding) is firm and reliable. The positive and negative poles must not be connected incorrectly. The fixing clamps must be firmly fixed and the outer insulating sheath of the capacitor must not be damaged. The voltage divider resistor should be connected as it is and the resistance value should be measured to ensure that the voltage divider is uniform.

(3) For electrolytic capacitors that have been stored for more than one year, the leakage current value should be measured and should not be too large. Before installation, add DC power for aging. Add a low DC power first. When the leakage current decreases, increase the voltage. Finally, at the rated voltage, check that the leakage current value must 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 + and - 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 is connected to the busbar or the area surrounded by the + and - busbars is large, causing the pulse overvoltage on the power module to rise, thereby damaging the power module or the overvoltage absorption device. In the case of a last resort, a high-frequency and high-voltage surge absorption capacitor can be installed on the inverter module with a short line to help absorb the overvoltage of the busbar and compensate for the damage caused by the extension of the capacitor connection busbar.