WEG CFW500 trips F0021 at power-up, what to check?
My WEG CFW500 inverter keeps tripping with F0021 (DC Link Undervoltage) right when I power it up. The supply voltage seems fine, and I've checked the input fuses. What should I look at next?
The F0021 fault on a WEG CFW500 inverter indicates that the DC link voltage has dropped below its minimum threshold for the configured supply. This can happen due to issues with the incoming power supply, incorrect voltage settings, or internal inverter faults. If the supply is stable and fuses are good, the pre-charge circuit is a likely suspect.
Likely causes and checks
1Supply voltage too low
- Points to it
- The incoming supply voltage to the inverter is below the required level, causing the DC link voltage to fall below the trip threshold. This often coincides with plant-wide power dips.
- Check
- Measure the actual supply voltage and compare it to the inverter's nameplate rating. Also, check parameter P0052 for the DC link voltage at the time of the last fault.
2Wrong supply voltage or P0296 setting
- Points to it
- The inverter is either connected to a supply voltage that doesn't match its rating, or parameter P0296 (supply voltage setting) is incorrectly configured for the actual supply.
- Check
- Verify that the inverter's label matches the actual supply voltage and that P0296 is set correctly (0 for 200-240 Vac, 1 for 380-480 Vac, 2 for 500-600 Vac).
3Phase fault in the input
- Points to it
- One or more input phases are missing or have an issue, leading to an insufficient DC link voltage, especially when the inverter is under load.
- Check
- Inspect all input fuses, the supply cabling, and confirm that all three supply phases are present and healthy.
4Fault in the pre-charge circuit
- Points to it
- The internal pre-charge circuit, which slowly charges the DC link capacitors at power-up, is faulty. This prevents the DC link from reaching the required voltage.
- Check
- If the supply and fuses are healthy and F0021 repeats, particularly at power-up, the pre-charge circuit is likely at fault. This requires referring to WEG service as it's an internal component.
Next check: Since you've already checked the supply and fuses, and the fault occurs at power-up, the next step is to suspect a fault in the inverter's internal pre-charge circuit. This typically requires professional service.
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