system and mission avionics is supplied by two DC
powered three phase mission inverters (fig. 2-30).
The mission ACIDC power cabinet (fig. 2-31) is
located in the mission rack, aft of the copilot's seat AC
power may be applied through an external power
receptacle located on the underside of the left wing, just
outboard of the engine nacelle.
DC POWER SUPPLY.
One nickel-cadmium battery furnishes DC power
when the engines are not operating. This 24-volt 34-
ampere/hour battery, located in the right wing center
section, is accessible through a panel on the top of the
wing. DC power is produced by two engine-driven 28
volt, 400-ampere starter-generators. Controls and
indicators associated with the DC supply system are
located on the overhead control panel (fig. 2-13) and
consist of a single battery switch, two generator switches,
two DC digital voltmeters, and two DC digital loadmeters.
Battery Switch A switch, placarded BATTERY -
OFF/RESET - ON (fig. 2-13), is located on the overhead
control panel under the MASTER SWITCH (gang bar).
The BATTERY switch controls DC power to the aircraft
bus system through the battery relay, and must be ON to
allow external power to enter aircraft circuits. When the
MASTER SWITCH (gang bar) is placed aft, the
BATTERY switch is forced OFF.
With battery or external power removed from
the aircraft electrical system due to fault,
power cannot be restored to the system until
OFF/RESET, then ON.
Generator Switches. Two switches (fig. 2-13),
placarded GENERATOR # 1 and # 2 are located on the
overhead control panel. These switches control electrical
power from the designated generator to paralleling circuits
and the bus distribution system. Switch positions are
placarded RESET, ON, and OFF. RESET is forward
(spring loaded back to ON), ON is center, and OFF is aft.
When a generator is removed from the aircraft electrical
system, due either to fault or from placing the
GENERATOR switch in the OFF position, the affected
unit cannot have its output restored to aircraft use until
the GENERATOR switch is moved to RESET, then ON.
Master Switch. All electrical current may be shut
off using the MASTER SWITCH gang bar (fig. 2-13)
which extends above the battery and generator switches.
The MASTER SWITCH (gang bar) is moved forward
when a battery or generator switch is turned on. When
moved aft, the bar positions each switch to the OFF
DC Load and Voltmeters. Four digital meters,
located on the overhead control panel (fig. 2-13), display
voltage readings and show the rate of current usage from
the left and right generating systems. The two loadmeters
indicate output amperage as a percent of rated capacity
from the respective generator. Current consumption is
indicated as a percentage of total output amperage
capacity for the generating system being monitored The
two voltmeters indicate bus voltage for the respective
Battery Volt/Ammeter. The mission control panel
(fig. 4-1), located in the fuselage sidewall adjacent to the
copilot's seat, incorporates a digital volt/ ammeter that
Minimum battery voltage for engine starting is 22 VDC.
Battery Charge Monitor. Nickel-cadmium battery
overheating will cause the battery charge current to
increase if thermal runaway is imminent The aircraft has a
charge-current sensor which will detect a charge current
The charge current system senses battery current through
a shunt in the negative lead of the battery. Any time the
amperes for 6 seconds or longer, the amber BATTERY
CHARGE annunciator and the MASTER CAUTION
annunciator will illuminate. Following a battery engine
start, the caution annunciator will illuminate approximately
six seconds after the generator switch is placed in the ON
position. The annunciator will normally extinguish within
two to five minutes, indicating that the battery is
approaching a full charge. The time interval will increase
if the battery has a low state of charge, the battery
temperature is very low, or if the battery has previously
been discharged at a very low rate (i.e., battery operation
of radios or lights for prolonged periods). The caution
annunciator may also illuminate for short intervals after
landing gear and/or flap operation. If the caution
annunciator should illuminate during normal steady-state
cruise, this indicates that conditions exist that may cause
a battery thermal runaway. if this occurs, the battery
current should be monitored using the battery ammeter.
If battery current continues to increase, the battery is in
thermal runaway and should be selected OFF and may be
turned back ON only for gear and flap extension and
approach to landing.
Generator Out Warning Annunciators. Two
caution/advisory annunciator panel fault annunciators
inform the pilot when either generator is not delivering
current to the aircraft DC bus system. These
annunciators are placarded #1 DC GEN and #2 DC GEN.