TM 55-1520-240-23-7
9-1
DIRECT CURRENT (DC) POWER DISTRIBUTION SYSTEM
9-1
DESCRIPTION
There are four sources of dc power for the helicopter:
Two 200 ampere transformer-rectifiers (for the No. 1
and No. 2 dc systems), an 11-ampere-hour battery,
and external dc power. The transformer-rectifiers and
external dc power provides 24 vdc to one or more
of five separate buses, located within the No. 1 and
No. 2 power distribution panels (PDP). The buses
distribute the power to all dc electrical components on
the helicopter.
The No. 1 PDP contains buses for the No. 1 dc system,
battery and switched battery, and half of the essential
bus. The No. 2 PDP contains the No. 2 dc system bus
and the other half of the essential bus.
During normal operation, power is available at all five
buses. When only battery power is available, 24 vdc is
available at the battery, switched battery, and essential
buses. When external dc power is applied, power is
available at the No. 1, No. 2, essential, and switched
battery buses. The battery bus is powered only by the
battery.
The only control switch for the system is the battery
on-off (BATT) switch on the overhead electrical panel
in the cockpit. The master caution panel has lights to
indicate the status of the system.
Most of the electrical connectors used on the aircraft
have a fully-coupled indicator which is utilized to
prevent over or under engagement of the connector
by the installer, and is also utilized during inspection
as a quick visual indication of proper installation. This
indicator consists of three axial stripes, usually blue
in color, placed on the plug shell which will align with
three corresponding stripes on the coupling ring when
completely coupled. Do not over-tighten the coupling
ring beyond the blue stripes.
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