7-70
P/N 11934-003
Section 7
Cirrus Design
Airplane Description
SR20
BAT & ALT Master Switches
The rocker type electrical system MASTER switches are ON in the up
position and OFF in the down position. The switches, labeled BAT 2,
BAT 1, ALT 1, ALT 2 are located in the bolster switch panel
immediately below the instrument panel. These switches, along with
the AVIONICS power switch, control all electrical power to the
airplane.
Battery Switches
The BAT 1 and BAT 2 switches control the respective battery. Setting
the BAT 1 switch ‘on’ energizes a relay connecting BAT 1 to the MCU
Distribution Buses (also energizing the circuit breaker panel buses)
and the open contacts of the starter relay. Setting the BAT 2 switch
‘on’ energizes a relay connecting BAT 2 to the circuit breaker panel
Essential Buses. Normally, for flight operations, all master switches
will be ‘on.’ However, the BAT 1 and BAT 2 switches can be turned
‘on’ separately to check equipment while on the ground. Setting only
the BAT 2 switch ‘on’ will energize those systems connected to the
circuit breaker panel Essential Bus. If any system on the other buses
is energized, a failure of the Distribution Bus interconnect isolation
diode is indicated. When the BAT 1 switch is set to ‘on,’ the remaining
systems will be energized. To check or use avionics equipment or
radios while on the ground, the AVIONICS power switch must also be
turned on.
Alternator Switches
The ALT 1 and ALT 2 switches control field power to the respective
alternator. For ALT 1 to start, the BAT 1 switch must be ‘on.’ Setting
the ALT 1 switch ’on’ energizes a relay allowing 28 VDC from the ALT
1 circuit breaker (Main Bus 2) to be applied to voltage regulator for
ALT 1. For ALT 2 to start, either the BAT 1 switch or the BAT 2 switch
must be ‘on.’ Setting the ALT 2 switch ’on’ energizes a relay allowing
28 VDC from the ALT 2 circuit breaker (Essential Bus) to be applied to
voltage regulator for ALT 2. Positioning either ALT switch to the OFF
position removes the affected alternator from the electrical system.
• Note •
Continued operation with the alternators switched off will
reduce battery power low enough to open the battery relay,
Revision A5
Summary of Contents for SR20
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