SNs 24-190 through 24-229,
25-030 through 25-064 except 25-061
The battery bus may be powered by external
power if the voltage from the GPU is 33 ±2
VDC or less. The batteries are connected to the
battery charging bus when the battery switch
is placed to ON. As long as the battery switch
is in ON, either engine generator charges both
batteries. The engine generators supply all
DC equipment on the airplane when the bat-
tery switch is in OFF except the batteries and
the hot-wired items.
Battery Charging Bus
The battery charging bus is the central distri-
bution point of the DC power from the batter-
i e s , a G P U , o r t h e g e n e r a t o r s t o va r i o u s
airplane systems. The DC voltmeter reads di-
rectly from this bus. The battery switch con-
nects the batteries to the battery charging bus
through the battery relay.
With the battery switch turned on, the entire
electrical system may be powered for a lim-
ited time. Exceptionally high amperage equip-
ment shortens this time considerably. A relay
isolates the Freon air conditioner and auxil-
iary heater until a GPU is connected or a gen-
erator is on and operating.
Generator Buses
The left and right generator buses are in the
current limiter panel in the tailcone. The gen-
erator buses may be powered by the battery
charging bus or by the output of the respective
generator.
The 275-ampere current limiters connect the
generator buses to the battery charging bus.
Feeder Buses
The left and right feeder buses receive power
from the respective generator buses or from the
opposite generator and feeder bus through the
50-amp DC bus-tie circuit breaker. The left
feeder bus provides power through circuit
breakers for primary navigation, communi-
cations, instruments, and one-half the DC
loads. The right feeder bus provides power
through circuit breakers for secondary navi-
gation, communication, instruments, and the
remaining half of the DC loads.
Each bus is protected by two circuit breakers
and two current limiters. On airplanes SNs
24-190 and 25-030 and subsequent, the feeder
buses are protected by a single bus circuit
breaker and overload sensor.
2A-16
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international