. 
 DC standby bus

Copyright . The Boeing Company. See title page for details.
Electrical -System Description 737 Flight Crew Operations Manual

.
hot battery bus

.
switched hot battery bus. The switched hot battery bus is powered whenever the battery switch is ON. The hot battery bus is always connected to the battery. There is no switch in this

circuit. The battery must be above minimum voltage to operate units supplied by this bus. An amber BAT DISCHARGE light comes on when excessive battery discharge is detected.
Dual Battery YA613 - YA722, YA809 - YK104
Two 24 volt nickel–cadmium batteries, main and auxiliary, are located in the electronics compartment. The batteries can supply part of the DC system. The auxiliary battery operates in parallel with the main battery when the battery is powering the standby system. At all other times, the auxiliary battery is isolated from the power distribution system. Battery charging is automatically controlled. Two fully charged batteries have sufficient capacity to provide standby power for a minimum of 60 minutes. Battery voltage range is 22–30 volts.
DC busses powered from the battery following a loss of both generators are:
.
battery bus

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 DC standby bus

.
hot battery bus

.
switched hot battery bus. The switched hot battery bus is powered whenever the battery switch is ON. The hot battery bus is always connected to the battery. There is no switch in this

circuit. The battery must be above minimum voltage to operate units supplied by this bus. An amber BAT DISCHARGE light comes on when excessive battery discharge is detected.
Battery Charger Transformer/Rectifier
Single Battery YA801 - YA803
The purpose of the battery charger is to restore and maintain the battery at full electrical power. The battery charger is powered through AC ground service bus 2.
The battery charger provides a voltage output tailored to maximize the battery charge. Following completion of the primary charge cycle, the battery charger reverts to a constant voltage TR mode. In the TR mode, it powers loads connected to the hot battery bus and the switched hot battery bus. The battery charger TR also powers the battery bus if TR3 fails. With loss of AC transfer bus 1 or the source of power to DC bus 1, the AC and DC standby busses are powered by the battery/battery charger.
Copyright . The Boeing Company. See title page for details.
6.20.12  September 26, 2003

Electrical -System Description 737 Flight Crew Operations Manual
Dual Battery YA613 - YA722, YA809 - YK104
The purpose of the battery chargers is to restore and maintain the batteries at full electrical power. The main battery charger is powered through AC ground service bus 2. The auxiliary battery charger is powered through AC ground service bus 1.
The battery chargers provide a voltage output tailored to maximize the battery charge. Following completion of the primary charge cycle, the main battery charger reverts to a constant voltage TR mode. In the TR mode, it powers loads connected to the hot battery bus and the switched hot battery bus. The main battery charger TR also powers the battery bus if TR3 fails. With loss of AC transfer bus 1 or the source of power to DC bus 1, the AC and DC standby busses are powered by the main and auxiliary battery/battery chargers.
The auxiliary battery charger and battery are isolated from the power distribution system under normal operation. When the main battery is powering the standby system, the auxiliary battery is connected to operate in parallel with the main battery.
Copyright . The Boeing Company. See title page for details.
Electrical -System Description

DC Power System Schematic
YA801 - YA803

Copyright . The Boeing Company. See title page for details.
6.20.14  February 15, 2001

Electrical -System Description 737 Flight Crew Operations Manual
YA613 - YA722, YA809 - YK104

Copyright . The Boeing Company. See title page for details.
September 26, 2003  6.20.15
Electrical -System Description 737 Flight Crew Operations Manual

Standby Power System
Normal Operation
The standby system provides 115V AC and 24V DC power to essential systems in the event of loss of all engine or APU–driven AC power. The standby power system consists of:
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static inverter

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AC standby bus

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DC standby bus

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battery bus

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hot battery bus

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switched hot battery bus

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main battery
YA613 - YA722, YA809 - YK104

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auxiliary battery. During normal operation the guarded standby power switch is in AUTO and the battery switch is ON. This configuration provides alternate power sources in case of partial power loss as well as complete transfer to battery power if all normal power is lost. Under normal conditions the AC standby bus is powered from AC transfer bus 1. The DC standby bus is powered by TR1, TR2, and TR3; the battery
　
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