Soft Charge Circuit Fault

What does UV3 mean?

The pre-charge contactor opened while the Drive was running, indicating a problem with the soft charge circuit. This is often caused by dirty contacts on the soft charge contactor, preventing it from functioning mechanically, and can lead to immediate shutdown and failure to start.

• Contactor/relay contacts (often internal to the drive) for the soft charge circuit are dirty, pitted, or worn, preventing reliable closure.
• Control signal loss to the soft charge contactor coil, causing it to open prematurely during the run state.
• Failure of internal soft charge circuit components (e.g., pre-charge resistors, control PCB) allowing the contactor to disengage.
• Excessive inrush current during power-up or transient voltage spikes damaging the soft charge resistors or contactor.
• Mechanical binding or failure of the soft charge contactor itself, preventing it from remaining closed when energized.

Click steps to track your progress.

1. 1

   Safely disconnect all power to the drive and wait for the DC bus indicator to extinguish (below 50VDC).

2. 2

   With power off, manually inspect the soft charge contactor (if accessible) for visible damage, pitting, or carbon buildup on the contacts.

3. 3

   Measure the resistance across the soft charge resistors (often located near the DC bus capacitors) to ensure they are within specification and not open circuit.

4. 4

   Verify the control voltage signal to the soft charge contactor coil during power-up and running states. Ensure it remains energized when the drive is running.

5. 5

   Check the mechanical integrity of the soft charge contactor, ensuring it pulls in and holds reliably when energized, and releases cleanly when de-energized.

6. 6

   Monitor the DC bus voltage during power-up to ensure it charges smoothly and rapidly to nominal voltage before the soft charge contactor attempts to open.