Inrush Current Limit Circuit Fault

What does Inrush current limit circuit fault mean?

The resistor of the inverter's inrush current limit circuit has overheated. This typically occurs due to frequent power cycling (ON/OFF) of the inverter, which causes the inrush current limiting components to work excessively, leading to thermal stress and potential failure. Overheating can degrade or destroy these components, preventing proper inverter startup.

• Frequent power cycling (ON/OFF) of the inverter without sufficient cool-down time for the inrush resistors.
• Failure of the bypass contactor that shorts out the inrush current limiting resistors after startup.
• Overload or short circuit downstream in the DC bus or output stage, causing continuous high current through the inrush circuit.
• Degradation or improper sizing of the inrush current limiting resistors themselves.
• External component fault (e.g., brake unit) drawing excessive current during initial power-up.

Click steps to track your progress.

1. 1

   Reduce the frequency of inverter power cycling to allow adequate cooling time for inrush components.

2. 2

   Power OFF the inverter, measure resistance of the inrush current limiting resistors (typically located near input terminals) using a multimeter.

3. 3

   Inspect the bypass contactor (often a small internal contactor) for proper operation; verify its coil energizes and contacts close shortly after power ON.

4. 4

   Check for short circuits or excessive load currents immediately downstream of the inverter's DC bus.

5. 5

   Verify the DC bus voltage builds up correctly after power application (e.g., 540-620VDC for 400V class).