(c)
In the charge mode, the battery charger supplies a constant current of 38 amps to the battery until the battery is fully charged. If charging current falls below 21 |5 amps, the current trips the battery current monitor's charging output, causing the main battery charger detection relay K10245 to close. Contacts on K10425 connect the charger INOP pin on the charger to EICAS. The EICAS system will display a MAIN BAT CHGR message to indicate a failed charger. When the battery is fully charged, the charger switches to the constant voltage (28v dc) mode and charging current goes to zero.
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(d)
If an undervoltage condition is sensed on the left DC bus or if an autoland signal is present, the main battery transfer relay will de-energize. When this occurs the main battery relay is energized. The energized main battery relay connects the battery bus to the hot battery bus and switches the main battery charger to operate in the T-R mode.
(e)
If the STBY POWER switch is set to BAT position, the charger is disconnected from the ground service bus by the MBCDR. The ground circuit for the main battery transfer relay opens, energizing the main battery relay. The hot battery bus and battery bus are connected. The battery is not charging. The contacts of K10425 are open, disconnecting the charger shutdown annunciation circuit from EICAS. The message is inhibited as it is grounded through the STBY POWER switch which is in series with the normally closed contacts of K10425.
(f)
A thermal switch in the battery closes when battery temperature exceeds 150°F (65°C). The switch closes a circuit to ground to energize the MBCDR. The MBCDR removes input power to the battery charger. The switch will re-open when battery temperature drops below 135°F (57°C).
(g)
If the battery is discharging at a rate greater than the battery current monitor threshold current the monitor closes a circuit to ground. The amber DISCH light on the standby power control panel (P5) will come on. EICAS computers will show a battery discharging message.
(h)
EICAS computers monitor battery voltage and current measurements. Other inputs include charger inoperative status and BAT switch position.
(2) APU Battery System (Fig. 3)
(a)
The APU battery and charger are connected to the APU battery bus, and supply bus loads.
(b)
AIRPLANES WITH 30-MINUTE STANDBY POWER; In normal operation, the ABCIR is de-energized. The APU battery charger is connected to the ground service bus. The charger operates in the charge mode only.
(c)
AIRPLANES WITH EXTENDED STANDBY POWER; In normal operation, the ABCIR is de-energized. The APU battery charger is connected to the ground service bus. The charger operates in the charge mode only. The APU battery current monitor latches APU battery charger detection relay K10418. Contacts on K10418 connect the charger INOP pin of the charger to EICAS. If charger shutdown occurs, the charger INOP pin goes high, turning on the message APU BAT CHGR INOP.
(d)
AIRPLANES WITH EXTENDED STANDBY POWER; The APU battery charger interlock relay is energized when starting the APU or when the STBY PWR switch is set to the BAT position. When energized, the relay disconnects the APU battery charger from the ground service bus. The APU BAT DISCH warning light (P5) and EICAS message are disabled during an APU start.
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