DC-3 Electrical System.

DC-3 Operations Manual – Electrical

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6-1  Power Supply
The electrical system is a 24 volt DC, single wire type.  The structure of the aircraft serves as a ground except for circuits in the vicinity of the magnetic compass, in which the ground is away from the compass.
Power Supply

1.  Battery circuits
2.  Aircraft batteries – two 12 volt 88 ampere hour batteries are connected in series to provide 24 volts to the bus.  Each battery is mounted on a carriage located within a box below the fuselage floor.  Access is through two drop down panels on the outside of the nose section of the fuselage.
3. Ground power – an external power plug is installed in the bottom of the fuselage forward of the wing leading edge.  An amber light installed in the center of the overhead switch panel in the cockpit indicates when power is being furnished to the external power plug irrespective of battery switch position.  The battery switch should be placed in the external power position when power is plugged in.
4. Battery switch – A single 3 position switch is installed on the right overhead switch panel in the cockpit to select aircraft batteries or ground power, with a center position for OFF.