MD Helicopters 369-500, Maintenance Instructions Manual

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CSP-HMI-3
MD Helicopters, Inc
.
MAINTENANCE MANUAL
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96-30-00
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The information disclosed herein is proprietary to MD Helicopters, Inc.
Neither this document nor any part hereof may be reproduced or transferred to
other documents or used or disclosed to others for manufacturing or any other
purpose except as specifically authorized in writing by MD Helicopters, Inc.
Copyright
©
1999 − 2016 by MD Helicopters, Inc.
DC ELECTRICAL LOAD DISTRIBUTION
MAINTENANCE PRACTICES
1. Description and Operation
2. Power Distribution Equipment
Power supply, distribution, and control
equipment consists of voltage generation,
regulation, power control components, and
wiring harnesses. This equipment switches,
controls, and routes dc electrical power to
functional electrical equipment and compo­
nents of the helicopter.
The wire harnesses have shielding to minimize
EMI. Separation of cables and relocation of
relays and contacts to the power distribution
center also help minimize EMI. Forward and
aft line relay contacts protect main power bus
and feeder wires. Over voltage diodes protect
circuits from excessive ground power voltages.
Switches, controls and circuit breakers are
installed at various locations, depending on
helicopter model (369D, 369E, 369FF, 500N or
600N) and instrument panel configuration
(slim-line, T-panel and T-panel with center
console).
NOTE:
369E helicopter S/N 384 and subs and
369FF helicopter S/N 076 and subs have
major power distribution differences. The
wire harnesses have additional shielding to
minimize EMI. Separation of cables and re­
location of relays and contracts to power dis­
tribution center. Forward and aft line relay
contacts protect main power bus and feeder
wires. Over voltage diodes protect circuits
from excessive ground power voltages and a
GCU (generator control unit) replaces the
over voltage relay (K103), voltage regulator
(VR1), and reverse current relay (K300).
The GCU will provide the necessary voltage
regulation, over voltage and reverse current
protection.
3. Power Distribution
(Effective on the following helicopters:
369D helicopter S/N 001 and subs,
369E helicopter S/N 001 - 383, and
369FF helicopter S/N 001 - 075)
NOTE:
369D model helicopters S/N 003 - 723
did not have an APU or battery relay. The
BATTERY-OFF-EXT PWR (master) switch
S2 connects the dc main power bus to either
an external power source or the nicad bat­
tery; or when OFF, disconnects the bus from
either of the two sources.
Nominal 28 Vdc power is supplied by the
starter-generator in its generator mode.
Voltage output is controlled by voltage
regulator VR1, at engine speeds of idle or
greater, by varying generator field current.
Overvoltage when sensed at VR1, closes
overvoltage relay K103 to open the SWITCH
circuit reverse current relay K300, removing
generator output from the main dc power bus.
Power is stored in a 24 Vdc high ampere hour
nickel-cadmium battery BT101. Reverse
current relay K300 prevents discharge of the
battery through generator circuits whenever
generator output voltage is less than battery
voltage. If the generator output is excessively
low, the ALARM circuit of the reverse current
relay lights the GEN OUT indicator on the
instrument panel. GEN circuit breaker
protects the generator field circuit from
currents over 15 amperes. For engine starting,
the START circuit causes voltage regulator
VR1 to open the generator field circuit, setting
the starter-generator in a start mode. Auxilia­
ry power receptacle J100, protected by APU
relay K309, provides an alternate source of 28
Vdc power for the helicopter when on the
ground. Master switch S2 directs power from
either APU relay K309 or battery relay K310
to main dc power busses W1, W2, and W3.
(Effective on the following helicopters only:
369E helicopters S/N 384 and subs,
369FF helicopters S/N 076 and subs,
500N helicopters S/N 001 and subs,
and 600N helicopters S/N 0003 and subs)
Nominal 28 Vdc power is supplied by the
starter-generator in its generator mode.
Voltage output is controlled by the generator
control unit (GCU) at engine speeds of idle or
greater, by varying generator field current.
The GCU regulates the voltage of the genera­
tor output and opens the aft line contactor