The inverter filter electrolytic capacitor shows clear signs of failure. The aluminum casing is swollen, the plastic outer sleeve is cracked, and there is visible leakage of the electrolyte. The safety valve has either been activated or pushed out, and the top of the capacitor is cracked. The terminals and cover are heavily corroded, with visible deformation and peeling, indicating that the capacitor is damaged. Using a multimeter, we found an open circuit or short circuit, with a significantly reduced capacitance and severe leakage (the resistance stabilizes at a low value after some time).
Analyzing the cause of the capacitor failure, several factors could be involved:
1. Poor quality of the capacitor itself—such as high leakage current, excessive loss, insufficient voltage rating, presence of impurities like chloride ions, poor internal structure, and a shorter lifespan.
2. A faulty rectifier bridge before filtering allowed AC voltage to directly enter the capacitor, causing it to fail.
3. A damaged voltage divider resistor led to uneven voltage distribution, which caused one capacitor to break down first, followed by others.
4. Improper installation, such as damage to the insulation, incorrect electrical connections, or poor soldering, resulted in poor contact and overheating.
5. Inadequate heat dissipation caused the capacitor to overheat over time, leading to damage.
When replacing the electrolytic capacitor, it's best to use the same model. If the original is unavailable, ensure that the replacement has the same voltage rating, leakage current, capacitance, size, polarity, and installation method. It's also important to choose a capacitor that can handle large ripple currents and has a longer lifespan.
During disassembly and reassembly, pay close attention to the electrical connections—whether through screws or soldering. These should be secure and reliable. Make sure the positive and negative terminals are correctly connected, and the fixing clamp is firmly in place. Avoid damaging the outer insulation of the capacitor. Reconnect the voltage divider resistor properly and check its resistance to ensure even voltage distribution.
For capacitors stored for more than a year, measure the leakage current before installation. It should not be too high. Before mounting, apply a low DC current for aging. Once the leakage current decreases, gradually increase the voltage. Ensure the leakage current does not exceed the standard during this process.
If the replacement capacitor is not the exact size and must be installed in a different location, be cautious about the busbar length between the inverter module and the capacitor. The busbar should not be longer than the original, and the area enclosed by the + and - busbars should be as small as possible, ideally using twisted pairs. This helps reduce inductance, preventing pulse overvoltage from damaging the power module or overvoltage protection components. As a last resort, a high-frequency surge-absorbing capacitor can be added near the inverter module using a short wire to help absorb any busbar overvoltage caused by the extended connection.
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