24-30
Page 2
Serials w/ Perspective Avionics
EFFECTIVITY:
CIRRUS AIRPLANE MAINTENANCE MANUAL MODELS SR22 AND SR22T
15 Dec 2014
B. DC Generation - Serials w/ Perspective Avionics
During normal operation, the alternators feed their respective distribution bus independently (ALT 1
feeds Main Distribution Bus 1 and ALT 2 feeds Main Distribution Bus 2). The main distribution buses
are interconnected by an 80-amp (Serials 22-3026 thru 22-4045, 22T-0001 thru 22T-0689) or 60-amp
(Serials 22-4046 & subs, 22T-0690 & subs) fuse and diode. The diode prevents ALT 2 from feeding
Main Distribution Bus 1. Additionally, since ALT 2 voltage is slightly higher than ALT 1 voltage, bus volt-
age is further assured.
The alternators are three-phase AC generator type; each alternator has an internal rectifier. Each
alternator uses two diodes for each phase to rectify the output. In addition, these diodes will block
reverse current. If a single output diode were to fail, the winding junction will be held to the output
potential, reducing the quantity of current the alternator can produce.
The alternators are regulated by the MCU and power the MCU via 6 AWG tin plated copper wires.
Alternator 1 is protected by an 100-amp fuse within the MCU while alternator 2 is protected by a 80-
amp fuse within the MCU. ALT 1 is connected to the Main Distribution Bus 1 and ALT 2 is connected to
the Main Distribution Bus 2. Each alternator system has its own 5-amp alternator circuit breaker
located in the circuit breaker panel. Each alternator is individually protected against overvoltage gener-
ation by the field control module, located within the MCU. ALT 1 is regulated to 28 volts and ALT 2 is
regulated to 28.75 volts.
Voltage output of each alternator is a function of engine RPM, alternator design, and load on the alter-
nator. During low RPM operation, the alternator will require higher engine RPM to provide the same
voltage to increased electrical loads.
The drop off RPM for each alternator will change whenever the electrical system loads are altered from
nominal. Any time an alternator drops off line, a Crew Alerting System (CAS) message will appear on
the MFD. If an alternator drops off line due to low engine RPM, the alternator can be restarted by sim-
ply increasing engine RPM. When alternator 2 drops off line, alternator 1 will power the Essential Bus
through the Main Distribution Bus 1 in the MCU. When alternator 1 drops off line, alternator 2 will
power the Essential Bus through the Main Distribution Bus 2 in the MCU. For additional information
concerning power distribution, see Electrical Load Distribution. (Refer to 24-50)
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