Cause : DC undervoltage comes when the DC link voltage drops below the undervoltage limit, the adjustable frequency drive checks if a 24 V DC backup supply is connected. If no 24 V DC backup supply is connected, the adjustable frequency drive trips after a fixed time delay. The time delay varies with unit size.

• Make sure that the supply voltage matches the adjustable frequency drive voltage.
• Perform input voltage test.
• Perform soft charge circuit test.