Compaq Pro UPS 500 Operation And Reference Manual page 37

"ON" Mode
Function: ENABLES battery backup.
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UPS Conditions: The UPS battery is charging. Power is ON at the UPS
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receptacles. The green LINE STATUS indicator (
Setting Advantages: Provides battery backup in the event of a blackout
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or brownout.
"STANDBY" Mode
Function: DISABLES battery backup.
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UPS Conditions: The UPS battery is charging. Power is ON at the UPS
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receptacles. The green LINE STATUS indicator (
UPS audio alarm is sounding once per minute.
Setting Advantages: Continues to charge the battery when power is
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present, while turning OFF the inverter to prevent battery backup
operation when equipment is not in use.
CAUTION: When the UPS is in the STANDBY mode, the UPS will not provide
battery backup during a blackout or brownout.
Other Modes of Operation
The ON and STANDBY UPS operating modes can be manually selected by
the user. There are, however, three additional UPS operating modes which
occur automatically.
Battery Operate Mode: While the UPS is in the ON mode and a
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blackout or severe brownout occurs, the UPS will automatically switch
to battery power. The yellow ON BATTERY indicator (
illuminated. AC power from the UPS battery is available at the
Battery-and-Surge-Protected receptacles. AC power is not available at
the Surge-Protected receptacles. An audio alarm sounds (the alarm can
be muted).
Automatic Shutdown Mode: When the UPS detects that less than
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2 minutes of battery power is available during a prolonged blackout or
brownout at approximately full load, the UPS will automatically enter
Automatic Shutdown mode. The red BATTERY LOW/REPLACE
indicator ( ) is illuminated. Less than 2 minutes of AC Power is

available at the Battery-and-Surge-Protected receptacles. A
non-silenceable alarm sounds as the UPS prepares for shutdown.
Operation 3-5
) is illuminated.

) is flashing. The

) will be