777 AIRCRAFT MAINTENANCE MANUAL
BATTERIES -MAIN AND APU BATTERY CHARGERS
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BATTERIES -FUNCTIONAL DESCRIPTION
General
The battery charger supplies power to dc buses and keeps the battery charged. It operates in these four modes:
*
Main
*
Topping
*
Float
*
TR.
Main Mode
The battery charger starts main mode operation when one of these conditions occurs:
*
Power turns on the battery charger
*
Battery has low voltage during float mode
*
Battery charger stops TR mode operation.
The main mode is the fastest charge mode. It has an initial 65 amps maximum output. The battery charger uses the increase in battery temperature to find that the battery is almost fully charged. This can take from a few minutes to an hour depending on battery charge and temperature. The temperature sensor in the battery gives the temperature data to the battery charger. The charger stops the main mode when the battery temperature increases 7F (4C). The maximum voltage in this mode is limited to 31v dc.
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Topping Mode
The battery charger automatically starts the topping mode at the end of main mode. The topping mode supplies less current than the main mode. The battery charger uses the topping mode to make sure that the battery is fully charged. The battery charger operates in the topping mode for 11 minutes.
Float Mode
The battery charger automatically starts the float mode at the end of the topping mode. The battery charger stays in the float mode when the battery is fully charged. It can supply 65 amperes to the dc bus while it is in float mode.
TR Mode
In the dddTR mode, the battery charger operates as a TRU and can supply up to 65 amperes to the dc bus. The output voltage of the TR mode is more closely regulated than the output voltage of the float mode.
The battery charger goes into the TR mode when there is a hot battery condition or when it receives a TR mode signal from the ELMS. The TR mode overrides all other modes. The hot battery condition occurs when the battery is 145F (63C) or hotter. The ELMS supplies the TR mode signal when any of these conditions occur:
*
Main battery relay energizes
*
Ground power battery relay energizes
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BATTERIES -FUNCTIONAL DESCRIPTION
* Autoland system sends an isolation request.
There is no ELMS TR mode signal for the APU battery charger.
Fault Protection
The battery charger monitors the battery for these conditions:
*
Overheat switch closed (160F (70C))
*
Colder than -40F (-40C)
*
Cell imbalance
*
Temperature sensor failure.
The cell imbalance condition occurs when the voltage of the first 10 battery cells is different from one half of the battery voltage. The battery charger monitors the voltage comparator in the battery to find this condition.
If the battery charger finds a fault, it turns off and sends a fault signal to the ELMS.
The battery overheat switch also sends a signal to the ELMS to show an EICAS message.
Current Indication
The current sensor sends current data to the EEU in the P310 panel.
Battery Cooling Fan
The battery cooling fan moves air through the battery case. The cooling fan motor comes on when all these conditions occur:
*
Battery temperature at least five degrees higher than the ambient temperature
*
Ambient temperature between -40C and 70C
*
Battery voltage normal, or battery voltage greater than 12 volts and the overheat switch is closed.
The cooling fan case has a press to test swich on it. The fan comes on if you push the switch and the 20C switch is closed.
NOTE: Fan operation times of several hours (even with airplane power removed) are possible under certain normal conditions. Extended fan operation does not show a problem with the battery.
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777 AIRCRAFT MAINTENANCE MANUAL
BATTERIES -FUNCTIONAL DESCRIPTION
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