DC under voltage

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If the DC-link voltage drops below the undervoltage limit, the drive checks for a 24 V DC back-up supply. If no back-up is connected, the drive trips after a fixed time delay, which varies by unit size. This usually indicates an issue with the mains supply.

• Severe drop in incoming mains voltage (e.g., brownout, complete power failure, or severe phase imbalance).
• Loose connection or high impedance in the incoming mains power circuit (e.g., input choke connections, damaged cables).
• Faulty input rectifier bridge within the drive (e.g., one or more open diodes preventing full DC voltage).
• Incorrectly configured or absent 24V DC back-up supply (if applicable) for the control section.
• Sudden, heavy load on the motor causing a transient voltage dip too severe for the drive to compensate.

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1. 1

   Measure the incoming AC line-to-line voltage at the drive's input terminals (e.g., L1-L2, L2-L3, L3-L1) and confirm its stability.

2. 2

   Inspect all connections of the incoming mains power cables at the drive's input terminals (e.g., X1) for tightness and corrosion.

3. 3

   Verify the continuity and proper operation of any upstream fuses or circuit breakers (e.g., F1, F2, F3).

4. 4

   If a 24V DC back-up supply is expected, measure its voltage at the designated input terminals (e.g., +24V, GND) on the control board.

5. 5

   Check the drive's internal DC-link capacitance for signs of bulging or leakage, indicating degradation.