Electrical System; Power Generation - Cirrus SR22 Pilot Operating Handbook

Cirrus Design Section 7
SR22 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 instrumentation, lighting, and other electrically operated
and controlled systems during normal operation.

Power Generation

Primary power for the SR22 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 gear-driven, internally rectified, 60-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 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
222) below the parachute canister. BAT 2 is charged from the circuit
breaker panel Essential Bus.
The Master Control Unit (MCU) is located on the left firewall. The MCU
controls ALT 1, ALT 2, starter, landing light, external power, and power
generation functions. In addition to ALT 1 and ALT 2 voltage
regulation, the MCU also provides external power reverse polarity
protection, alternator overvoltage protection, as well as alternator fail
P/N 13772-001 7-65
Revision A5