DC-3 Operations Manual – Electrical

DC-3 Electrical PanelDownload the DC-3 Manual-Electrical System PDF

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.

Generators

  1. 1.   A P-1 generator rated for 200 amps is installed on each engine.
  2. The system operates as one individual unit.  Both generators through the controls and batteries are connected in parallel to one bus bar.
  3. One generator with the batteries will provide ample power for operation of all required equipment.

Generator controls

  1.  Switch relay – each generator circuit is equipped with a switch relay which is operated by bus voltage through the respective generator switch.  When the generator switch is OFF, the equalizer and field circuits are interrupted and the generator’s voltage output will drop to residual voltage (.5 – 2 volts)
  2. Voltage regulator – the voltage regulator automatically controls generator output within desired limits regardless of changes in engine RPM or electrical load.
  3. Reverse current relay – the reverse current relay is an automatic switching device.  This unit connects the generator to the bus when generator output is normal and will disconnect the generator from the bus when there is a reverse current flow from the bus to the generator.  The relay is operative only when the generator switch is on.
  4. Circuit breakers – each generator is protected by a 200 amp circuit breaker located on the circuit breaker panel in the companionway.
  5. Flashing generators – the generator flashing switches are located on the circuit breaker panel and provide a means for “flashing” each generator field in the event voltage output is not indicated.  These switches should be depressed momentarily only for best results. CAUTION:  DO NOT FLASH GENERATOR IF VOLTAGE IS INDICATED – SEE FLASHING PROCEDURE IN THE CHAPTER.
  6.  Voltmeter – the voltmeter is located on the circuit breaker panel in the companion way and has a 3-position momentary selector switch for checking voltage output of each generator or voltage at the bus.
  7. Ammeter – there is one ammeter for each generator on the right overhead switch panel that indicates electrical load of each respective generator.

Electrical Control Panels

Electrical panels for the distribution and control of power to the various electrical circuits are as follows:

  1.  Cockpit electrical panel – located above the windshield overhead each pilot’s position consisting of 2 units separated by the ignition switch panel.
  2. Hostess electrical panel – located on the bulkhead adjacent to the buffet.
  3. Circuit breaker panel – located in the companionway forward of the radio rack.

Landing lights – two landing lights are provided as an integral part of each wing and are controlled by two switches located on the left electrical control panel.  Each light may be operated independently.

Position lights – Six position lights consist of the following:

  1. Wing tip lights-left wing tip RED right wing tip GREEN
  2. Tail lights – Top (clear) WHITE  Bottom light RED
  3. Fuselage lights – Top of fuselage (clear) WHITE  Bottom of fuselage (clear) WHITE
  4. NOTE:  Position lights may be selected OFF, STEADY, OR FLASHING

Anti collision light

  1. The anti collision light is installed on top of the vertical stabilizer and is controlled by a switch located on the Pilot’s overhead panel.

Miscellaneous equipment

  1. Spare landing light bulb – located in a box taped to the air duct
  2. Other spare bulbs – located in a box above the First Officer’s seat
  3. Aldis lamp – located aft of the Captain’s seat
  4. Passing light (red) located in the left landing light nacelle.

LIMITATIONS

  1. Generator Voltage 27.7 +_ .1
  2. Generator paralleling – 20 amp max differential
  3. Generator amperage – 200 amp max continuous

 

6-3  TROUBLE SHOOTING

 

Trouble –  No amps – voltage normal (one generator)

Correction

  1. Check 200 amp circuit breaker
  2. Turn OFF faulty generator switch and observe ammeter of good generator.
    • If amperage increases (approximately doubles) turn ON the generator switch and resume operations.
  3.  If the amperage on the operative generator does not increase (see above) turn ON faulty generator switch and turn OFF good generator switch.
    • If the faulty generator (ammeter) indicates a load wait several minutes and turn ON good generator switch.  If both generators now indicate a load but are out of balance (more than 20 amps) turn OFF high load generator and continue operation on one generator.
    • If the faulty generator does not indicate a load continue operation of the good generator only.

Trouble – No amps No volts

Correction

  1. Turn faulty generator OFF
  2. Engage flashing switch momentarily for faulty generator and observe voltage indication.
  •  If voltage is now normal, turn generator ON and resume normal operation.
  • If no voltage indication is obtained, turn faulty generator switch OFF and continue operation on good generator.

Trouble – No bus voltage on ground power

Correction

  1. Check battery switch on BATT CART
  2. Check ground power amber light, if light is no ON check ground power output.

Trouble – Amperage too high on both generators

Correction

  1.  Turn off all unnecessary electrical equipment.  See emergency procedures.

Trouble – Excessive spread between ammeters ( more than 20 amps)

Correction

  1.  Turn high load generator OFF for several minutes then return to ON

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