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Section 6 - Weight & Balance
Weight and balance data for the dual alternator system is provided
with the Equipment List for each delivered airplane.
Original: 09-28-99
6 of 10 P/N 11934-S10
Section 9 Cirrus Design
Supplements SR20
Section 7 - Systems Description
Electrical System
The airplane is equipped with 28-volt direct current (VDC) electrical
system. The system provides uninterrupted power for avionics, flight
instruments, lighting and other electrically operated and controlled
systems during normal operation.
Power Generation
Primary power for the SR20 is supplied by a 28-VDC negative-ground
electrical system. The electrical power generation system consists of a
24-volt, 10-amp-hour battery, two alternators, and a master Control
Unit (MCU). The MCU contains an Alternator Control Unit (ACU) for
each alternator, contactors for starter, battery, and ground power, a
landing light relay, circuit protection for the circuit breaker panel buses,
and modules for other protection and annunciation functions. The
battery is an aviation grade, 12-cell lead-acid type with non-spill vent
caps. The battery is used for engine starting and as an emergency
power source in the event of alternator failure.
Two rectified alternators provide constant charging current for the
battery and primary power to the aircraft electrical system during
normal system operation. The forward, belt-driven alternator is
designated ALT 1. The aft, engine-driven alternator is designated ALT
2. Although each alternator produces the same amount of power at a
given rotational speed, ALT 1 rotates faster and is rated at 75 amperes
while ALT 2 is rated at 40 amperes. Paralleling circuits in the function
modules balance alternator output so that, under normal operating
conditions, ALT 1 provides 60% of the electrical power and ALT 2
provides the remaining 40%.
Each alternator’s ACU provides transient suppression and constant
voltage regulation of the alternator output. To protect sensitive
instruments, over-voltage circuits monitor each alternator’s output and
automatically limit peak voltage to 28.5 volts. In the event an
over-voltage or an overload condition occurs, the associated ACU
automatically opens the affected alternator’s circuit breaker. With the
alternator off line, the associated ALT FAIL light illuminates, and the
other alternator will provide 100% of the electrical power requirements.
Original: 09-28-99
P/N 11934-S10 7 of 10
Cirrus Design Section 9
SR20 Supplements
Should both alternators fail, the battery will supply system current and
a discharge rate will be indicated on the ammeter. Under these
conditions, depending on electrical system load, the LOW VOLTS
warning light will illuminate when system voltage drops below
approximately 24.5 volts.
Power Distribution
The power distribution system for the SR20 consists of the primary
electrical power bus in the MCU, which distributes electrical power
from the alternators, battery, and external power receptacle to the
airplane systems through the circuit breaker panel and internal circuit
breakers or fuses. The circuit breaker panel main busses (Main Bus 1
and Main Bus 2) and a non-essential bus receives power through 25-
amp circuit breakers on the primary power bus in the MCU. The
Essential Bus in the circuit breaker panel is dual sourced receiving
power from the ESSENTIAL 1 and ESSENTIAL 2 circuit breakers on
the respective Main Bus. Nonessential avionics are powered from
Main Bus 1 through the associated AVIONICS circuit breaker.
Essential avionics is powered from the Essential Bus through the
associated AVIONICS circuit breaker. During normal operation the
essential and non-essential busses operate in parallel, but during
power system failures, the non-essential bus can be disconnected to
provide load shedding of non-essential equipment loads. This load
shedding system is designed to increase emergency operating power
capacity and to decrease pilot workload during emergency situations
by providing the capability to remove all non-essential loads in a single
action.
BAT & ALT Master Switches
Rocker type electrical system MASTER switches for the battery (BAT)
and both alternators (ALT2 and ALT) are installed on the bolster switch
panel. The right switch, labeled BAT, controls the battery contactor.
When the BAT switch is set ‘on,’ battery power is available to the
airplane electrical circuits. The ALT2 master switch controls the aft,
gear-driven alternator. The ALT master switch controls the forward,
belt-driven alternator.
　
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本文鏈接地址：西銳20飛機信息手冊 SR22 AIRPLANE INFORMATION MANUAL 1148-126(96)