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SECTION 7 CESSNA
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AIRPLANE AND SYSTEMS DESCRIPTION MODEL 2088 (675 SHP)
ELECTRICAL SYSTEM
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The airplane is equipped with a 28-volt, direct-current electrical system
(see Figure 7-12). The system uses a 24-volt lead-acid battery; or a
24-
volt sealed lead acid battery; or a 24-volt Ni-Cad battery, located on the
,~
front right side of the firewall, as a source of electrical energy. A 200-
amp engine-driven starter-generator is used to maintain the battery's
state of charge. Power is supplied to most general electrical and all
avionic circuits through two general buses, two avionic buses and a
battery bus. The battery bus is energized continuously for memory
keep-alive, clock and cabinlcourtesy light functions. The two general
buses are on anytime the battery switch is turned on. All DC buses are
on anytime the battery switch and the two avionic switches are turned
on.
An optional standby electrical system, which consists of an
engine-
driven alternator and separate busing system, may be installed in the
airplane. For details of this system, refer to Section
9,
Supplements.
GENERATOR CONTROL UNIT
Tne generator control unit (GCU) s mounted nside the cabin on the left
forward fuselaae sdewall. Tne
un,t orovldes the electrical control
functions necessary for the operation of'the starter-generator. The GCU
orovides for automatic starter cutoff when enaine RPM is above 46.
Below 46, the starter-generaror functions as astaner, and above 46,
rhe starter-aeneraror functions as
a
aenerator wnen the starter switch is
OFF. The
~CU
provides voltage re&lation plus high voltage protection
and reverse current
~rotection. In the event of a hiah-voltaae or reverse
current condition, the generator is automatically
dkconneEted from the
buses. The generator contactor (controlled by the GCU) connects the
generator output to the airplane bus. If any GCU function causes the
generator contactor to de-energize, the red GENERATOR OFF light on
the annunciator panel will come on.
GROUND POWER MONITOR
The ground power monitor 1s located ns~de the
electrical
power control
assemblv mounred on rhe left hand s~de of the flrewall In the enalne
compartmenr. This unit senses the voltage level applied to the exteynal
power receptacle and w ll close the external power contacror when the
applied volrage is
withln tne proper lim ts. In addition, the ground power
monitor senses a'r~lane bus voltaae and w,ll lluminate tne VOLTAGE
LOW light on the annunciator
pang1 when bus voltage drops to battery
voltage.
1
7-82 U.S. Revision
23
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