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units.
Battery temperature monitoring and overtemperature warning for
NICAD batteries are provided via the EICAS/MFD displays and the
Crew Warning Panel (CWP). The above is described further under
ELECTRICAL SYSTEM INDICATORS in this section and under
BATTERY OVERHEAT.
In the event of a dual generator failure, the aircraft batteries, in
conjunction with the emergency battery, will provide power for the
necessary essential equipment for a limited duration. For more
information, see DUAL GENERATOR FAILURE in this section.
EMERGENCY BATTERY
The standard emergency battery installed is one 24-vdc, 10-amp-hour,
lead-acid battery which is located in the nose section of the airplane. A
larger 18-amp-hour battery may be installed as an option. The emergency
battery is connected to the emergency battery bus when selected
On, but only provides power to that bus when the electrical system is
not being powered by a GPU, APU or airplane generator. The emergency
battery also provides power to both emergency hot buses even with
the emergency battery selected OFF. The emergency battery provides
power to the emergency battery bus in the event of a dual generator
failure or an inflight electrical fire. The installation also enables the essential
and essential avionics buses to be powered by the emergency
battery in isolation from the main system during the engine start sequence,
thus preventing problems caused by engine start voltage fluctuations.
This is described further under DISTRIBUTION in this
section.
The emergency battery is charged by the airplane electrical system and
provides power to the emergency bus for a limited time if the airplane
dc generators fail. See DUAL GENERATOR FAILURE in this section
for more information.
A shunt, located between the emergency battery and the emergency
battery contactor allows for monitoring of battery recharge and
discharge current. If the emergency battery is selected to On and a
battery discharge current is sensed by the shunt, the white EMER
caption on the EMER BATT switch will illuminate, indicating
emergency battery discharge. A white EMER BATT annunciator on the
Pilot’s Manual
4-4 PM-126A
CWP will also illuminate for this condition. Battery charging from the
airplane generators precludes these indications under normal
operation. The emergency battery has the same battery depletion
protection on the ground as the main batteries.
The shunt also monitors emergency battery charging. If it exceeds 10
amps for 1 minute, an amber EMER BATT LOW will be displayed on
the CAS alerting the crew to an emergency battery recharging
condition.
The emergency battery voltage can be checked by observing the EMERV
or EMER BUS VOLTS on the EICAS/MFD SUMRY or ELEC systems
schematic displays prior to applying GPU, APU or airplane generator
power to the electrical system.
Eleven different components are connected directly to the emergency
battery bus and will be available when that bus is being powered by the
emergency battery, aircraft generator, GPU or APU. Main airplane
batteries alone will not power the emergency battery bus because the
isolation contactors will both be open if both generators are off-line.
The EMER BATT is selected On before engine start and remains on
throughout the flight. When the EMER BATT switch on the electrical
control panel is depressed, current from the emergency battery closes
the emergency battery contactor and the OFF indication on the switch
extinguishes.
When the emergency battery is selected OFF, the contactor will open
and the OFF indication on the switch will illuminate, assuming at least
one essential bus is still powered by another power source.
GENERATORS
Two engine-driven starter/generators, one on each engine accessory
section, provide the normal source of 28-vdc power to the airplane.
Each starter/generator is equipped with a “quick attach/detach”
mounting to facilitate maintenance. Unless a GPU is powering the airplane
electrical system, the generator will automatically come on line
when the DEEC determines the engine is up to speed (approximately
95% of N1 idle). If a GPU is used for engine start, the generators will automatically
come on line after the engines are running when the GPU
is disconnected, or when the EXT PWR switch on the electrical control
panel is depressed, changing the annunciation from ON to AVAIL.
Pilot’s Manual
PM-126A 4-5
In flight, cooling air is routed from a scoop on the associated engine
nacelle to the starter/generator. Cooling while on the ground is
provided by a fan mounted on the generator shaft.
　
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