Electrical System
Electrical System Comprised of:
- 28 VDC, 300 AMP Starter/Generator
- 24 VDC lead acid battery 42 AMP
- 24 VDC Auxiliary Battery
Electrical Power is distributed through:
- Battery Bus
- Generator Bus
Circuit Breakers Provide Protection and are located in both cockpits
- Battery Bus on Left Console Panels
- Generator Bus on the Right Console Panels
Numbers to Know
- 22.0 Volts minimum needed for external power engine start
- 23.5 Volts minimum needed for engine start just using the battery (battery start)
- GEN needs to supply at least 25.0 Volts to charge the battery
- AUX Battery supplies backup power for approximately 30 minutes
Starter/Generator
- Is primary provider of aircraft power
- Provides 28 VDC power which is sufficient to operate all equipment on Gen and Batt Buses and
charge the battery
NOTE The generator needs to supply a minimum 25 volts to charge the battery
- Generator Switches are located in each cockpit
o Moving Gen Switch On Turns Gen Power On
o Moving the Gen Switch to from OFF to ON trips the switch in the other cockpit with the
switch in the ON position – power remains uninterrupted while control of switch is
transferred
o If the GEN malfunctions in flight
 GEN may be reset in flight with the GEN Reset Button
 Cycle the GEN by turning the GEN OFF and ON
o If the GEN warning illuminates on the EICAS display, the air conditioning is the only
equipment automatically shed is the air conditioning
- Power is provided through the GEN SW circuit breaker located on the front cockpit generator
bus
Battery
- 24 VDC lead acid 42 AMP
-
Provides power for engine starts and is capable of powering all electrical systems except air
conditioning
- BATT switches in each cockpit and
- Moving BATT switch from OFF to ON trips the switch in the other cockpit to OFF and transfers
control to the cockpit with the switch in the ON position.
- While control of the BATT switches is switched between cockpits, power remains uninterrupted
- Power is provided through the BAT SW circuit breaker located on the front cockpit battery bus
Auxiliary Battery
- 24 VDC 5 AMP
- Located in the left avionics compartment
- Controlled by AUX BAT switch
- AUX BATT power is tested by turning the BAT Switch ON and then holding the AUX BAT test
switch for a minimum of 5 seconds
- Power is provided through the AUX BAT circuit breaker located on the front cockpit battery bus
NOTE – In an emergency situation, the auxiliary battery powers the backup flight instrument(BFI), radio
relays, Inertial Reference Unit (IRU), standby VHF control, Fire 1 fire warning system for 30 Minutes
NOTE – With only AUX Battery power available, excessive radio transmissions reduce available battery
time
External Power
- Ext PWR receptacle is installed in the left, aft fuselage, below the left avionics bay door.
- EXT PWR is distributed on the battery bus and is controlled by the battery switch
- Aircraft is internally protected from the external power over/under voltage.
o A voltage sensor is located between the external power connector and the external rely
 If the external voltage level exceeds a nominal level, the external power will be
disconnected from the aircraft electrical system
CAUTION – Do not connect external power if battery voltage is below 22.0 volts. Connecting external
power could cause damage to the aircraft.
Bus Tie Switch
- Located on the front cockpit right console
- Used to tie/isolate the battery and generator buses
- With BUS TIE in NORM the generator feeds both generator and battery bus items
- If the BUS TIE fails or is set to OPEN, the amber BUS TIE Caution on the EICAS illuminates,
separating the battery and generator buses.
- If the battery or battery bus fails (red BAT BUS warning on the EICAS illuminated) while the BUS
TIE caution is illuminated, items on the battery bus will not be powered
- If the generator fails while the BUS TIE caution is illuminated, items on the generator bus will
not be powered. Expect a minimum of 30 minutes of battery power to the battery bus items.
- If the generator has failed and the BUS TIE switch is in the NORM position, then the battery
powers all items except the air conditioner, but for a reduced amount of time.
o
If only the generator bus (red GEN BUS warning on EICAS illuminated) has failed, the
items on the generator bus will not powered, but if the BUS TIE switch is in the NORM
position, the generator continues to power the battery bus and charge the battery.