ELECTRICAL POWER SUPPLY AND DISTRIBUTION
2.47 ELECTRICAL POWER SYSTEM.
All the helicopter electrical power requirements are sup-
plied by two ac generators, two transformer/rectifiers
(T/Rs) and in the case of complete failure, a 24-volt bat-
tery will supply flight critical systems. For ground opera-
tions, 115 vac external power can be supplied to the heli-
copter through the external power receptacle. The
electrical power distribution system is shown in figure
2-38. The system caution lights are listed in tables 2-4 and
In the event any circuit breaker opens for
unknown reasons, do not attempt to re-
set the breaker more than one time. Re-
peated tripping of a circuit breaker is an
indication of a possible problem with
equipment or electrical wiring. Multiple
attempts to reset the circuit breaker may
result in equipment damage and/or an
2.47.1 DC Power Supply System.
Two essential ac
busses supply power to the two 350-ampere T/Rs through
the XFMR RECT 1 and XFMR RECT 2 circuit breakers on
the pilot overhead circuit breaker panel (fig 2-39). The
No.1 and No. 2 T/Rs convert the ac input to 28 vdc. The 28
vdc power is applied to a dc contactor, which routes 28
vdc from T/R No. 1 to the No. 1 essential dc bus and from
T/R No.2 to the No. 2 essential dc bus. The No. 1 and No.
2 essential dc buses each apply 28 vdc, in parallel,
through isolation diodes to power the emergency dc bus
during normal operation. For emergency operation, the
battery powers the emergency dc bus, and the emergen-
cy dc bus diodes isolate the battery from the noncritical
loads. The two essential dc buses also supply 28 vdc
power to the No. 3 essential dc bus. The T/Rs are self-
monitoring for overtemperature and will illuminate the
HOT RECT 1 and HOT RECT 2 caution lights on the pilot
caution/warning panel when an overheat condition exists.
The dc contactor monitors the T/Rs for output loss or drop
in voltage. If the dc contactor senses a fault in T/R No. 1,
it disconnects T/R No. 1 from the No. 1 essential dc bus
and illuminates the RECT 1 caution light on the pilot cau-
tion/warning panel. At the same time, it connects No. 1 es-
sential dc bus to No. 2 essential dc bus through relay ac-
tion inside the contactor. The same action takes place if
T/R No. 2 fails. If both T/Rs fail, the ELEC SYS FAIL cau-
tion light on the CPG caution/warning panel will illuminate.
The caution/warning lights receive 28 vdc from the emer-
gency dc bus through the CAUT circuit breaker on the pi-
lot overhead circuit breaker panel and the EMERG BATT
CAUT circuit breaker on the CPG main circuit breaker
panel (fig 2-40).
A 24-volt, 13 ampere-hour, 19 cell, nick-
el-cadmium battery provides emergency power. The bat-
tery is located in the aft avionics bay. The battery is
charged by the battery charger which receives 28 vdc
power from the No. 1 essential dc bus through the BATT
CHGR DC circuit breaker and 115 vac from the No. 2 es-
sential ac bus through the BATT CHGR AC circuit break-
er. Both circuit breakers are on the pilot overhead circuit
breaker panel. The battery charger will completely charge
the battery and then maintain a trickle charge. The battery
charger also contains fault sensing that monitors battery
temperature, cell balance, and charger operation. If a fault
occurs, either the HOT BAT or CHARGER caution light
will illuminate on the pilot caution/warning panel. The heli-
copter is equipped with a battery heater which operates
automatically when the battery is on.
b. CPG Battery Override Switch.
guarded toggle BAT OVRD switch is located on the CPG
PWR lever quadrant (fig 2-12). With the guard down, the
switch is in the NRML position and enables the pilot EXT
PWR/BATT switch on the pilot ELEC PWR control panel
(fig 2-37) located on the left console (fig 2-11). When the
guard is positioned up and the switch is set to OVRD, the
pilot EXT PWR/BATT switch is inoperative, and the bat-
tery is disconnected from the emergency dc bus.
2.47.2 AC Power Supply System.
The ac power sup-
ply system is the primary source of electrical power. It sup-
plies 115 vac from two 35 kilovolt-ampere generators.
Each generator and its associated components comprise
an independent ac generating system that supplies about
one-half of the total electrical requirements to the ac
buses. The generators are mounted on, and driven by, the
main transmission accessory gear box. The 115 vac pow-
er is monitored and regulated by the generator control unit
(GCU). If the generator output is normal, the GCU applies
voltage to the ac contactor which energizes and connects
the generator output