DC Bus Undervoltage

What does UV1 mean?

The DC bus voltage inside the drive has fallen below the trip point (e.g., 190Vdc for 240V AC input or 380Vdc for 480V AC input), which is adjustable via L2-05. Common causes include insufficient incoming AC power, excessively short acceleration times leading to voltage sag, or significant fluctuations in the input voltage quality.

• Insufficient incoming AC line voltage to the drive's L1/R, L2/S, L3/T terminals, possibly due to grid instability or undersized supply transformer.
• Momentary power loss or sag in the main AC supply, causing the DC bus capacitors to discharge below the undervoltage trip level (L2-05).
• Faulty or worn pre-charge resistors/circuitry failing to adequately charge the DC bus capacitors.
• Damaged DC bus capacitors or internal power supply components within the drive, leading to reduced voltage holding capacity.

Click steps to track your progress.

1. 1

   Measure the incoming AC line voltage at the drive's L1/R, L2/S, L3/T terminals using a multimeter to confirm it is within 10% of the drive's nominal input voltage.

2. 2

   Verify the parameter L2-05 (DC Bus Undervoltage Detection Level) is set correctly according to the drive's nominal input voltage (e.g., 190V for 240V drive or 380V for 480V drive).

3. 3

   Inspect the wiring connections from the main power supply breaker to the drive's input terminals (L1/R, L2/S, L3/T) for loose connections or corrosion.

4. 4

   Monitor the DC bus voltage (dC bus monitor value) on the drive's operator panel during operation to observe its behavior relative to the L2-05 trip point.

5. 5

   If a dynamic braking unit is present, verify its functionality by checking for continuity across the braking resistor terminals and proper connection to the drive (B1, B2).