Specifications

SECTION II
AIRPLANE AND SYSTEMS
MODEL 560
DIRECT CURRENT (DC) POWER
The direct current (DC) power generation system consists of two starter/generators, two generator
control units, one battery, two DC ammeters, one aft power junction box (divided into left and right side
electrical circuits), one DC voltmeter, and control switches. Normally, the left generator powers the left
main DC bus and the right main DC bus receives power from the right generator. Both operate in parallel,
but in the event either generator is offline, the crossover bus acts as a cross tie so that the remaining
generator will power both main DC buses. The DC buses supply power for all DC functions except engine
starting.
Each main DC bus, as well as the emergency DC bus, is controlled by its own power relay. The
circuit breakers in Figure 2-19 are coded to indicate the equipment items powered by each main bus and by
the emergency bus.
The DC power indicators consist of two ammeters, a voltmeter and two amber generator failure lights.
The ammeters function as load meters indicating the load being carried by each generator.
The voltmeter is wired through the battery switch and will indicate the voltage of the hot battery bus
any time the battery switch is in the BATT or EMER position. The voltmeter selector switch can be rotated
to the L or R GEN positions to check generator voltage output. Since the voltmeter reads the highest
voltage on the bus, an accurate check of one generator is obtained only with the opposite one off line.
Should either generator fail, the associated power relay will open, removing the generator from the
system and illuminating the appropriate L or R GEN OFF annunciator panel light and the master caution.
Should both generators fail, the master warning light will also illuminate. This is the only condition under
which amber annunciator light illumination will trigger the master warning.
GENERATORS
A microprocessor controlled generator control unit provides starter regulation, overvoltage, feeder fault
and ground fault protection for each generator. Three-position L and R generator switches are marked
GEN, OFF and RESET. In the GEN position, generator control is automatic for regulation, protection and
load bus connection. This is the normal switch position for battery starting and all flight modes. Placing the
switch to OFF isolates the generator from its load bus. The momentary RESET position resets a generator
that has been tripped as a result of an overvoltage, feeder fault or engine fire switch actuation.
Each starter/generator is capable of a 50% overload (450 amps) for five minutes. A single generator
is capable of supporting the entire electrical system; however, should one generator go off line while in
flight, the vapor cycle air conditioning system will automatically be shed from the remaining generator due to
its high current draw.
JUNCTION BOX
The DC power junction box is located aft of the cabin centered at WL 127.00 and centerline of the
airplane. The junction box is a single box divided into left and right sides by a dividing wall. A single cover
closes the box. The J-box contains relays, current transformers, circuit breakers, fuse limiters, junction
blocks, printed circuit boards, shunts and terminal boards. Three number 6-gauge wires (feeder cables) are
routed independently of the main airplane wire bundles from each side of the power junction box to the
respective circuit breaker panel. The feeder cables are protected at both ends in the junction box by
individual 80-ampere fuse limiters and in the circuit breaker panel by 75-ampere circuit breakers. A wire
protected by a 20-ampere circuit breaker in the aft junction box connects the emergency circuit to the right
circuit breaker panel.
I 2-36 Configuration AA 56OMB-01