TM 1-1520-238-T-6
9–87
9–7.
SYSTEM DESCRIPTION (cont)
9–7
(3) Battery.
The battery supplies 24 VDC for APU starting and emergency dc operation with a total
electrical failure.
(a) When the battery quick disconnect connectors (fig. 9–79) are connected, battery voltage is applied
to the battery charger, the open contacts of the battery relay, and the coil of the battery relay through the battery
charger. With no other source of electrical power on the helicopter and the CPG’s power quadrant’s BAT OVRD
switch in the NRML position, placing the pilot’s ELEC PWR panel’s BATT/EXT PWR switch in the BATT position
applies a ground to the coil of the battery relay. The battery relay energizes, using battery voltage from the
charger. The battery relay connects the battery to the emergency dc bus which is isolated from dc essential buses
1 and 2 by CR1 and CR2.
(b) When either generator comes on line, power is supplied to dc essential bus 1 which supplies
28 VDC to the battery charger through the POWER BATT CHGR DC circuit breaker (CB85). The battery charger
deenergizes the battery relay by opening the circuit to the battery relay coil. As long as dc essential bus 1 has at
least 18 VDC applied, the battery charger maintains an open circuit to the coil of the battery relay and keeps the
battery in a charged state. When dc essential bus 1 falls below 18 VDC, the battery charger closes the circuit to
the battery relay coil, connecting the battery to the dc emergency bus. The battery remains connected to the dc
emergency as long as dc essential bus 1 remains below 18 VDC or until battery voltage falls below 9 VDC.
(c) The pilot’s caution/warning panel contains two indicators (HOT BAT and CHARGER) which monitor
the battery. The HOT BAT indicator advises that the battery has overheated, a cell imbalance exists, or heater
current is insufficent. The CHARGER indicator advises that the charger is not charging the battery. Refer to
TM 11-1520-238-23-2/TM 11-6140-203-14-2 for additional information on the battery and battery charger.
FAULT
SENSING
VOLTAGE
AND
TEMP
SENSING
DC ESS BUS 1
EMERG DC BUS
CR1
CPG BATT OVRD
SWITCH
EXT
PWR
BATT / EXT PWR
SWITCH
OFF
BATT
NORM
OVRD
DC ESS BUS 2
CR2
BATTERY
RELAY
NORMALLY
OPEN
BATTERY
CHARGER
+
-
BATTERY
PILOT
CAUTION / WARNING
PANEL
CHARGER
HOT BAT
POWER BATT
CHGR DC
CB85
M69-355
Figure 9–79.
Emergency DC Bus Functional Block Diagram
