Dell R640 PSUs blinking rapidly while on the UPS

Hello WINSF,

When a PowerEdge R640 PSU LEDs are blinking rapidly only when connected to the UPS, the most common causes are:

1.       UPS output power quality issue

o The R640's hot-plug PSUs are sensitive to abnormal input frequency, voltage fluctuations, or stepped/simulated sine-wave output.

o Some UPSs operate normally on utility power but switch to a stepped waveform on battery, causing PSU warning LEDs.

2.       PSU input mismatch

o If redundant PSUs are fed from different sources (for example, PSU1 from utility and PSU2 from UPS), the server can detect an input mismatch and flash PSU indicators.

3.       UPS overload or undersized UPS

o A fully configured R640 can draw significant power, especially during boot or high CPU utilization.

o If the UPS is near capacity, voltage sag can trigger PSU warnings.

4.       Grounding or wiring issue

o Improper grounding, bad PDUs, or faulty UPS outlets can cause both PSUs to indicate an AC input problem.

What the PSU LED pattern usually means

On Dell PowerEdge servers:

·         Green solid = normal operation.

·         Green blinking = PSU firmware update or PSU insertion event.

·         Rapid amber blinking = PSU fault or AC input issue.

·         Alternating patterns = PSU mismatch or redundancy problem.

Quick checks

From iDRAC or Lifecycle Controller, look for:

·         "Input lost"

·         "AC power error"

·         "PSU mismatch"

·         "Redundancy lost"

·         "Predictive failure"

Also verify:

·         UPS manufacturer/model

·         Whether both PSUs are plugged into the same UPS

·         Whether the blinking is green or amber

·         Whether the server logs any PSU events in iDRAC

Specific to Dell servers on UPSs

I've frequently seen this when enterprise servers are connected to:

·         Consumer APC Back-UPS units

·         Simulated sine-wave UPSs

·         UPSs operating on battery

The server runs, but the PSUs flash because they don't like the UPS output waveform. Moving the R640 to a pure sine-wave UPS often resolves the issue.

If you provide:

·         UPS make/model

·         PSU wattage (495W, 750W, 1100W, etc.)

·         LED color (green or amber)

·         Whether the problem occurs on utility power, battery power, or both

I can narrow it down to the most likely root cause.

@DELL-Sam L​ 

Please find the below responses in bold,

From iDRAC or Lifecycle Controller, look for: No any related logs

    UPS manufacturer/model: Prolink PRO701SFC (600VA UPS)

• Whether both PSUs are plugged into the same UPS : same UPS
• Whether the blinking is green or amber: green rapid flickering, not blinking 
• Whether the server logs any PSU events in iDRAC: No related logs
• Server PSU wattage 750W (Dell Product number: 057TFT)
  Whether the problem occurs on utility power, battery power, or both : Only on battery power
• Current server power consumption: 120W