(2)
The main/APU battery charger detection enable relay K10424 switches electrical power to relay K10418 and the APU battery current monitor from the battery bus to the ground handling bus whenever the ground handling bus is energized. This assures that the APU battery charging detection circuit is powered whenever the ground service bus, which powers the APU battery charger, is powered.
3. Operation (Fig. 2 and 3)
_________
A. Functional Description
______________________
(1)
Normal operation occurs when the STBY POWER switch on M10062 panel is in AUTO position. Standby bus power comes from the main AC and DC buses. The main battery transfer relay is energized. The AC standby power relay is energized, sending main AC power to the standby power relay. The standby power relay is de-energized, switching power to the standby buses. The bus off relays energize, breaking the ground connection to the standby bus off light and EICAS computers. The static inverter receives input power, but supplies no load.
(2)
If the left main AC bus loses power or an autoland signal is received, the main battery transfer relay de-energizes. The main battery relay energizes, connecting the hot battery bus to the standby bus, through the standby power relay. The AC standby power relay is de-energized, connecting the static inverter to the AC standby bus.
(3)
If only the left main DC bus loses power, the main battery transfer relay de-energizes. The main battery relay closes, supplying the DC standby bus from the hot battery bus. The AC standby bus is powered as normal.
(4)
Turning the STBY POWER switch to BAT position causes the system to operate as would occur if the left main AC bus lost power.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL
(5)
AIRPLANES WITH EXTENDED STANDBY POWER; the RCCB closes when the main battery relay closes. This parallels the main and APU batteries, except closure is inhibited during autoland or when starting the APU. Operation of the two batteries in parallel extends the standby power system endurance to 90 minutes. An EICAS status message APU BAT NO STBY is displayed if the RCCB does not close during the standby power mode or if it remains closed during normal operation when the batteries should be isolated.
(6)
Turning the STBY POWER switch to OFF position removes power from the standby bus. The amber OFF light on M10062 panel comes on. The EICAS computers display a standby bus off message.
(7)
The standby buses will be off if the BAT switch on M10062 panel is OFF and the main buses loses power. The standby buses will also be off if the BAT switch is OFF and an autoland signal is received.
(8)
EICAS computers monitor inverter output voltage and frequency, and standby bus status.
(9)
AIRPLANES WITH EXTENDED STANDBY POWER; EICAS also displays messages when the APU battery charger has failed, or when the APU battery is discharging.
(10)
Static inverter output voltage and frequency are displayed by the EICAS computer in the ELEC/HYD format. The static inverter output voltage and frequency are in the STBY/BAT column in the rows labled AC-V and FREQ.
(11)
Static inverter output voltage below 106v ac or above 124v dc will cause the EICAS status/maintenance message STBY INVERTER to be displayed and stored in EICAS non-volatile memory.
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