P/N 11934-003
7-67
Cirrus Design
Section 7
SR20
Airplane Description
Electrical System
The airplane is equipped with a two-alternator, two-battery, 28-volt
direct current (VDC) electrical system designed to reduce the risk of
electrical system faults. The system provides uninterrupted power for
avionics, flight instruments, lighting, and other electrically operated
and controlled systems during normal operation.
• Note •
Serials 1337 and subsequent with SRV standard
configuration:
The airplane is equipped with a single
alternator, dual battery electrical system. This configuration is
identical to the dual alternator system described below except
components used in conjunction with the secondary alternator
are removed.
Power Generation
Primary power for the SR20 is supplied by a 28-VDC, negative-ground
electrical system. The electrical power generation system consists of
two alternators controlled by a Master Control Unit (MCU) mounted on
the left side of the firewall and two batteries for starting and electrical
power storage.
Alternator 1 (ALT 1) is a belt-driven, internally rectified, 75-amp
alternator mounted on the right front of the engine. Alternator 2 (ALT
2) is a gear-driven, internally rectified, 20-amp alternator mounted on
the accessory drive at the rear of the engine. ALT 1 is regulated to 28
volts and ALT 2 is regulated to 28.75 volts. The output from ALT 1 is
connected to the Main Distribution Bus in the MCU through an 80-amp
fuse. The output from ALT 2 is connected to the Essential Distribution
Bus in the MCU through a 40-amp fuse. Both alternators are self-
exciting (not self-starting) and require battery voltage for field
excitation in order to start up - for this reason, the batteries and
alternators should not be turned off in flight.
Battery 1 (BAT 1) is an aviation grade 12-cell, lead-acid, 24-volt, 10-
amp-hour battery mounted on the right firewall. BAT 1 is charged from
the Main Distribution Bus in the MCU. Battery 2 (BAT 2) is composed
of two 12-volt, 7-amp-hour, sealed, lead-acid batteries connected in
series to provide 24 volts. Both BAT 2 units are located in a vented,
acid-resistant container mounted behind the aft cabin bulkhead (FS
Revision A5
Summary of Contents for SR20
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