PowerFlex 525 F004 UnderVoltage when large loads start, what to check?
Our PowerFlex 525 drive keeps tripping F004 UnderVoltage. It seems to happen whenever a large motor starts up on the same power feeder. What should I investigate first?
Fault F004 on a PowerFlex 525 indicates that the DC bus voltage has dropped below the drive's minimum threshold. This is a Type 1 fault, meaning it can be cleared by an auto-restart. Common causes include supply dips, lost phases, weak power supply, or upstream switching.
Likely causes and checks
1Weak supply or undersized transformer
- Points to it
- The drive trips when large loads start elsewhere on the same supply, indicating the power source may not be robust enough to handle the combined demand.
- Check
- Measure the drive input voltage while the large loads start and compare it with the drive’s rated input voltage range.
2Supply dip or short interruption
- Points to it
- The DC bus voltage fell below the minimum due to a temporary drop or interruption in the incoming AC line voltage.
- Check
- Compare F651 [Fault 1 BusVolts] and the fault time with power-quality or utility records, or log the line voltage during the next event.
3Blown input fuse or lost phase
- Points to it
- A blown fuse or lost phase can lead to an insufficient supply voltage, especially under load, causing the DC bus to drop.
- Check
- With the drive isolated, check the input fuses and line-side connections, then measure all three line-to-line voltages under load.
4Upstream switching while the drive runs
- Points to it
- If line power is removed while the drive is still commanded to run, the DC bus voltage will drop, triggering an UnderVoltage fault.
- Check
- Check the control sequence to ensure that line power is not removed before the drive is properly stopped.
Next check: Given that the fault occurs when large loads start, the most likely cause is a weak supply or undersized transformer. You should measure the drive's input voltage while these large loads are starting to see if it drops below the drive's rated input range.
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