FOR TRAINING PURPOSES ONLY
2-16
KING AIR C90GTi/C90GTx
PILOT TRAINING MANUAL
When external power is connected, a relay in
the external power sensor will close only if
the polarity of the voltage being supplied to
t h e e x t e r n a l p owe r r e c e p t a c l e i s c o r r e c t
(Figure 2-23).
Whenever an exter nal power plug is con-
nected to the receptacle and the BAT switch
is ON, the yellow EXT PWR annunciator
will illuminate, whether or not the exter nal
power unit is ON. If the EXT PWR annun-
ciator is flashing–and the exter nal power
unit is connected–then one of three condi-
tions exists: EXT PWR Switch is OFF, EXT
PWR voltage is low, or EXT PWR voltage
is too high.
Exter nal power voltage can be monitored
any time, even before the EXT PWR switch
on the pilot’s left subpanel is switched ON,
by tur ning the VOLTMETER BUS SELECT
switch in the overhead panel (Figure 2-3) to
the EXT PWR position and reading the volt-
age on the voltmeter.
A high-voltage sensor will lock out the ex-
ternal power relay if external power is above
31 ±0.5 volts DC.
W h e n t h e E X T P W R – O N – O F F – R E S E T
switch is switched ON, the exter nal power
relay closes. As exter nal power enters the
aircraft. the left and right generator bus tie
relays close, per mitting power to reach all
buses. Consequently, the entire electrical
system can be operated.
O b s e r ve t h e f o l l ow i n g p r e c a u t i o n s wh e n
using an exter nal power source:
NEVER CONNECT AN EXTER-
NAL POWER SOURCE TO THE
AIRPLANE UNLESS A BATTERY
INDICATING A CHARGE OF AT
L E A S T 2 0 VO LT S I S I N T H E
AIRPLANE. If the battery voltage
i s l e s s t h a n 2 0 vo l t s , t h e b a t t e r y
must be recharged, or replaced with
a battery indicating at least 20 volts,
before connecting external power.
O n ly u s e a n ex t e r n a l p owe r s o u r c e f i t t e d
with an AN-type plug. The auxiliar y power
unit must be regulated between 28.0 and 28.4
volts DC and be capable of producing 1000
amperes for 5 seconds, 500 amperes for two
minutes, and 300 amperes continuously. A
maximum continuous load of 350 amperes
will damage the exter nal power relay and
power cables of the air plane.
Voltage is required to energize the avionics
m a s t e r p owe r re l ay s t o re m ove th e p owe r
f r o m t h e av i o n i c s e q u i p m e n t . T h e r e f o r e ,
never apply exter nal power to the air plane
without f irst applying batter y voltage.
The batter y may be damaged if exposed to
voltages higher than 30 volts for extended
periods of time.
To preclude damage to the exter nal power
unit, disconnect external power from the air-
plane before applying generator power to
the electrical buses.
Refer to the “Nor mal Procedures” section
of the
POH
for procedural details of using
exter nal power.
AVIONICS MASTER POWER
The avionics systems installed on each air-
plane usually consist of individual nav/com
units, each having its own ON–OFF switch.
Avionics packages will vary on different air-
plane installations. Due to the large num-
ber of individual receivers and transmitters,
a Beech avionics master switch placarded
AVIONICS MASTER POWER is installed
o n t h e p i l o t ’s l e f t s u b p a n e l . A n Av i o n i c s
Master Power Schematic diag ram is shown
in Figure 2-8. Refer to the Avionics chapter
o f t h i s t r a i n i n g m a n u a l f o r d e t a i l s o f t h e
avionics system.
CAUTION
2
ELECTRIC
AL
POWER
SY
STEMS
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