Power Distribution - Cirrus SR22 Pilot's Operating Handbook And Flight Manual

Section 7
Systems Description

Power Distribution

Power is supplied to the airplane circuits through three distribution
buses contained in the MCU: Main Distribution Bus 1, Main
Distribution Bus 2, and the Essential Distribution Bus. The three
distribution buses power the associated buses on the circuit breaker
panel.
Master Control Unit
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 electrical
system health annunciations to the Integrated Avionics System. Power
is distributed to the airplane circuit panel buses through Main and
Essential buses in the MCU. The Main distribution buses are
interconnected by an 80-amp fuse and a diode. The diode prevents
ALT 2 from feeding the Main Distribution Bus 1. Additionally, since ALT
2 Bus voltage is slightly higher than ALT 1 voltage, bus separation is
further assured.
Essential Distribution Bus
The Essential Distribution Bus is fed by both Main Distribution Bus 1
and Main Distribution Bus 2 in the MCU through two 50-amp fuses.
The Essential Bus powers two circuit breaker buses through 30-amp
fuses located in the MCU:
• ESS BUS 1,
• ESS BUS 2.
Main Distribution Bus 1
The output from ALT 1 is connected to the Main Distribution Bus 1 in
the MCU through a 100-amp fuse. Main Distribution Bus 1 directly
powers the Landing Light through a 7.5-amp fuse and three circuit
breaker buses through 30-amp fuses located in the MCU:
• A/C BUS 1,
• A/C BUS 2,
• MAIN BUS 3.
7-48
Cirrus Design
SR22
P/N 13772-004
Original Issue