TM 55-1520-240-23-7
9-1
DIRECT CURRENT (DC) POWER DISTRIBUTION SYSTEM
(Continued)
9-1
TRANSFORMER-RECTIFIERS
Two transformer-rectifiers (TR) are the primary source
of dc power on the helicopter. Each transforms 115/200
volt 400 Hz ac power to 48.5 vac and rectifies it to
28 vdc. The No. 1 TR is located in the left electrical
equipment pod with the battery and the battery charger.
The No. 2 TR is in the right electrical equipment pod.
NO BREAK - WORK HARDER
Each TR assembly consists of an input filter, a step-down
transformer, rectifiers, an output filter, a step-down
autotransformer and a control relay. An integral cooling
fan draws air from inlets in the cabin at sta. 176. Air
from the pod is vented to the cabin near floor level.
NO BREAK - WORK HARDER
The dc output of the TR is not regulated. Regulation is
accomplished indirectly through regulation of the input
voltage. Each TR is protected by its own reverse current
cutout (RCCO) relay, located in the No. 1 or No. 2 power
distribution panel.
NO BREAK - WORK HARDER
If power from either of these primary dc power sources
is interrupted, a light on the master caution panel (NO. 1
RECT OFF or NO. 2 RECT OFF) will come on.
BATTERY
The battery subsystem includes a 24 volt
nickel-cadmium battery rated at 11 ampere hours, a
battery charger, a relay, status lights, and a caution light
on the master caution panel. The battery, charger, and
relay are located in the left electrical pod.
NO BREAK - WORK HARDER
When there is no other source of dc power, the battery,
when plugged in, supplies the battery bus and the
switched battery bus. When the cockpit battery switch is
on, it also supplies the essential bus.
BATTERY CHARGER
The charger monitors and controls the state of charge
of the battery. It is powered by 115/200 volt, 3 phase,
400 Hz ac from the No. 1 ac bus. A relay connects the
battery to the charger and the essential dc bus when the
battery switch on the cockpit overhead panel is on.
NO BREAK - WORK HARDER
BATTERY charge status lights are in the left electrical
pod. The CHARGING light indicates battery is on normal
charge (battery is less than 80 percent charged). The
CHARGE COMPLETE light indicates battery is on low
charge (battery is more than 80 percent charged).
NO BREAK - WORK HARDER
A BATT SYS MAL light on the master caution panel in
the cockpit comes on and charging stops when one or
more of the following conditions occur:
Battery or charger overtemperature.
Battery temperature sensor failure.
Battery cell imbalance.
Fault in charger circuits.
EXTERNAL POWER
A dc external power receptacle accepts the cable from
an external dc power supply cart to supply 28 vdc power
to the helicopter. The receptacle is located inside a
hinged access door at the forward end of the left pod.
NO BREAK - WORK HARDER
When an external source of dc power is used, the No.
1 and No. 2 transformer-rectifiers are automatically
disconnected. Power from the external source is applied
to the No. 1 and No. 2 dc buses and to the essential
and switched battery buses. An EXT PWR light on
the master caution panel comes on to indicate when
external power is being used, and is powered through
the dc external power relay.
NO BREAK - WORK HARDER
The application of external dc power will not charge
the battery.
9-11
