The inverter filter electrolytic capacitor shows visible signs of failure. The aluminum casing is swollen, the plastic outer sleeve is cracked, and there's leakage of the internal electrolyte. The safety valve has either popped open or been pushed out, and the top of the capacitor is cracked. The terminals and cover are severely corroded, with some parts deformed or missing, indicating that the capacitor is damaged. When tested with a multimeter, it shows an open circuit or short circuit, with a significantly reduced capacitance and serious leakage (the resistance stabilizes at a low value after testing).
Analyzing the cause of the capacitor failure:
1. **Poor quality of the capacitor itself**: This includes high leakage current, high losses, insufficient voltage rating, impurities like chloride ions, poor internal structure, and a shorter lifespan.
2. **Faulty rectifier bridge before filtering**: A damaged rectifier bridge can allow AC voltage to directly enter the capacitor, causing it to fail prematurely.
3. **Damaged voltage divider resistor**: If the resistor is faulty, it may lead to uneven voltage distribution across capacitors, causing one to break down first, which can then affect others.
4. **Improper installation**: Issues such as damage to the insulation, incorrect grounding, poor soldering, or loose connections can result in overheating and eventual failure.
5. **Inadequate heat dissipation**: Poor cooling conditions can cause excessive temperature rise, leading to long-term damage to the capacitor.
**Capacitor replacement recommendations:**
1. **Use the same model if possible**: If the original model isn't available, ensure that the replacement has the same voltage rating, leakage current, capacitance, physical dimensions, polarity, and installation method. Choose a capacitor that can handle large ripple currents and has a longer lifespan.
2. **Proper electrical connections**: During disassembly and reassembly, make sure all connections—whether screw-based or soldered—are secure and reliable. Ensure correct polarity, and avoid damaging the outer insulation. Reconnect the voltage divider resistor properly and check its resistance to ensure even voltage distribution.
3. **Check older capacitors**: If the capacitor has been stored for over a year, measure its leakage current. It should not be too high. Before installation, apply a low DC current to age the capacitor. Gradually increase the voltage once the leakage current decreases, ensuring it stays within acceptable limits.
4. **Consider busbar length and layout**: If the replacement capacitor is smaller and needs to be installed in a different position, keep the busbar from the inverter module to the capacitor as short as possible. Minimize the area enclosed by the + and - busbars, ideally using twisted pairs. This helps reduce inductance, preventing pulse overvoltage that could damage the power module or overvoltage protection components. In extreme cases, add a high-frequency surge capacitor near the inverter module using a short wire to help absorb any overvoltage caused by extended busbars.
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