Load Relay Fault

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A fault detected in the load relay, often related to capacitor charging. This can prevent the drive from energizing its DC bus properly or switching the output, leading to a failure to start or maintain operation and potential damage to internal components.

• Damaged pre-charge resistors (e.g., R1, R2) in the DC bus charging circuit, leading to high inrush current.
• Faulty or welded contacts of the main contactor or bypass relay responsible for connecting the DC bus to the main power stage.
• Open circuit in the control coil wiring for the load relay (e.g., K2 contactor), preventing its activation.
• Excessive DC bus voltage ripple or an overvoltage condition preventing the charging circuit from stabilizing.
• Internal control board fault preventing proper sequencing of the DC bus charging process at power-up.

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1. 1

   1. Disconnect input power. Measure resistance of pre-charge resistors (if accessible) and compare to manufacturer specifications (e.g., 20-100 Ohms).

2. 2

   2. Inspect the contacts of the main contactor or bypass relay for pitting, welding, or signs of overheating.

3. 3

   3. Check the control voltage (e.g., 24VDC) to the coil of the load relay/contactor and ensure it is stable during the power-up sequence.

4. 4

   4. With power OFF, verify continuity of the main contactor's power contacts when manually actuated (if possible).

5. 5

   5. Monitor the DC bus voltage during power-up using a multimeter to observe the charging sequence and identify any stalls below nominal voltage.