Delta MCS-1800 - Manual (Page 27)

DELTA MCS-1800 3U Power Shelf
Installation, Operations and
Maintenance Manual
8-2
8.3.2 Troubleshooting
The HV alarm is usually caused when the equalize voltage exceeds the HV threshold setting. Another
probable cause that the temperature compensation voltage exceeds the HV threshold during cold temperature
operation. During this alarm condition, the system continues to operate.
8.4 Low Voltage Alarm
8.4.1 Description
The Low Voltage alarm (LV) is a minor alarm activated when the DC output voltage decreases below the
LV threshold setting. When the system voltage decreases below the LV LED located on the ALU panel, and
activates the LV alarm contact. The rectifiers remain on line during this minor alarm condition. When the
system voltage increases above the threshold setting, the ALU extinguishes the LV LED and deactivates the LV
alarm contact.
8.4.2 Troubleshooting
The LV alarm condition occurs during a brownout condition or prior to a complete AC Fail condition
caused by commercial AC problem conditions.
Another probable cause is that the temperature compensation voltage decreases the float voltage below the
LV threshold during hot temperature operation. During this alarm condition, the system continues to operate.
8.5 Low Voltage Disconnect Alarm (System equipped with PDU)
8.5.1 Description
During an AC Fail condition, the rectifiers are shut down and the reserve batteries begin to discharge.
When the battery cells discharge below the LVD setting, the ALU lights the LVD LED on the ALU panel,
activates the LVDS OPEN alarm contact, and opens the LVDS contactor. When the AC recovers, the LVBD
recovers automatically. The ALU extinguishes the LVD LED and resets the normally closed set of alarm
contacts.
8.5.2 Troubleshooting
If the battery disconnect switch remains open after voltage is restored to the rectifiers, one of the following
is occurring:
1. The ALU may be faulty. Swap out the ALU with a spare and verify voltage settings.
2. The LVBD coil windings may be open. With a digital multimeter, check the LVBD coil windings.
8.6 Fuse/Circuit Breaker Fail Alarm (System equipped with PDU)
8.6.1 Description
If the DC load output fuse opens or battery switch trip off, the ALU sends the alarm condition, lights the
LED on the ALU panel, and activates the Fuse Fail alarm.
8.6.2 Troubleshooting
To troubleshoot the fuse/circuit breaker fail alarm condition, perform the following steps:
1. Verify that the fuse/circuit breaker is the proper size (use 80% derating guide).
2. Verify that the external fault that might cause fuse/circuit breaker tripping is removed.
3. Replace the blown fuse with a fuse with the same rating or of the corrected value. In case of a circuit