Inrush Current Limit Circuit Fault

What does E.IOH mean?

This fault occurs when the resistor within the inverter's inrush current limit circuit overheats. This typically happens due to frequent power ON/OFF cycles to the inverter, stressing the charging components, or an internal component failure. Prolonged overheating can damage the inverter's power supply section and lead to critical failures.

• Excessive frequency of main power ON/OFF cycles to the inverter's input (R/L1, S/L2, T/L3), preventing proper discharge of the DC bus.
• External input contactor or circuit breaker being cycled too rapidly, engaging the pre-charge circuit repeatedly.
• Failure of the main DC bus charging contactor (if present) to close properly after the pre-charge sequence, leaving the inrush resistor in circuit.
• Deterioration or failure of the inrush current limiting resistor itself due to thermal stress or aging.
• Overvoltage condition on the input power supply, increasing the charging current and thermal load on the resistor.

Click steps to track your progress.

1. 1

   Reduce the frequency of power cycling the main input power to the inverter; allow at least 10 minutes between power ON cycles.

2. 2

   Verify the proper operation and timing of the external input contactor, ensuring it closes only after the DC bus voltage stabilizes.

3. 3

   Check the DC bus voltage at terminals P/+ and N/- immediately after power-up; it should rise steadily to the nominal level (e.g., 540VDC for 400VAC input).

4. 4

   Visually inspect the inrush current limiting resistor (often a large ceramic component) for signs of overheating, charring, or cracking.

5. 5

   Use a multimeter to measure the input voltage (R/L1, S/L2, T/L3) to ensure it is within the inverter's specified operating range (e.g., 400V ±10%).