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Direction of current (charge or discharge).

The battery current data shows on page 1 of the MFD electrical maintenance page.
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777 AIRCRAFT MAINTENANCE MANUAL

BATTERIES -GENERAL DESCRIPTION

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BATTERIES -MAIN AND APU BATTERIES

Purpose
When ac power is not available, the main battery does these functions:
*
Supplies power to dc loads that are necessary for ground operation

*
Supplies power to all the components that deploy the RAT

*
Supplies standby system power until the RAT generator starts to supply power.

The main battery can supply standby system power for at least five minutes.
The APU battery supplies electrical power to start the APU.
Physical Description
The main battery and the APU batteries are rechargeable. They are fiber nickel-cadmium (FNC) batteries. Each battery weighs 106 lb (48 kg).
Each battery has two sets of ten FNC cells. The battery case is green. The case has two mounting flanges and two lifting handles. Bolts attach the mounting flanges to the airplane. The lifting handles help you connect ground support equipment (GSE) to the battery when you move it.
The battery has a terminal block and an electrical connector. The terminal block connects the high power output. The electrical connector connects control and status signals.
The battery has both ambient and battery temperature sensors, and an overheat switch (not shown). The battery cooling fan comes on when the battery gets hot.
Training Information Point
WARNING: BE CAREFUL WHEN YOU MOVE THE BATTERY. BECAUSE THE BATTERY WEIGHS 106 POUNDS (48 KG), INJURY TO PERSONS CAN OCCUR.
Use ground support equipment to lift the main battery. You install a rack and pulley between the floor beams above the battery to help you lift it.
The APU battery attaches to a tray that you can pull out to easily remove and install the battery. When you push the tray in, there are two captive screws you must tighten to prevent tray movement.
CAUTION:  DO NOT CHARGE THIS BATTERY WITH BATTERY CHARGERS WHICH ARE NOT APPROVED FOR THIS TYPE OF FNC BATTERY. OVER-CHARGING CAN OCCUR AND SERIOUSLY DAMAGE OR DESTROY BATTERY CELLS.
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BATTERIES -MAIN AND APU BATTERIES

The capacity of each battery is 47 amp-hours. The main battery can supply the hot battery bus loads for 10 days.
The main battery and the APU battery are interchangeable.
No maintenance is necessary for FNC batteries.
When no other power is on the airplane, the hot battery bus supplies power to the static random access memory (SRAM) of the AIMS. If you disconnect the main battery with no power to the AIMS cabinets, you lose some data. See the AIMS section for more information (SECTION 31-41).
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777 AIRCRAFT MAINTENANCE MANUAL

BATTERIES -MAIN AND APU BATTERIES

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BATTERIES -MAIN AND APU BATTERY CHARGERS

Purpose
The battery chargers change ac power to dc power for the related dc buses. The battery chargers keep the related batteries charged.
Physical Description
The battery chargers are ARINC 600-style LRUs. Each battery charger has these components on the front cover:
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Terminal block

*
Electrical connector

*
Handles.

The terminal block connects the high power output. The electrical connector connects ac power, control signals, and status signals to the battery charger.
Functional Description
The input power to each battery charger is 3-phase, 115v ac, 400 Hz. power.
The battery charger has four modes of operation. Three of these are charge modes; the other is transformer-rectifier (TR) mode.
In the TR mode, the battery charger supplies dc power up to 65 amps. The voltage of this power is very tightly regulated.
Training Information Point
The main battery charger and the APU battery charger are interchangeable.
CAUTION:  DO NOT TOUCH THE BATTERY CHARGER BEFORE YOU DO THE PROCEDURE FOR DEVICES THAT ARE SENSITIVE TO ELECTROSTATIC DISCHARGE. ELECTROSTATIC DISCHARGE CAN CAUSE DAMAGE TO THE BATTERY CHARGER.
　
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