% (11)Avionics Master Relay % The avionics master relay connects the main bus to the avionics bus. The AVIONIC MASTER
% switch controls the relay. % (12)Essential Avionics Relay % The Essential Avionics relay connects the essential bus to the essential avionics bus. The
% AVIONIC MASTER switch controls the relay.
% (13)AVIONIC MASTER switch
% With the avionic master switch set to OFF:
%) The avionic master relay is energized to disconnect the avionics bus from the main bus.
%) The essential avionics relay is energized to disconnect the essential avionic bus from the
% essential bus.
% With the Avionic Master switch set to ON,
%) The avionic master relay is de-energized to connect the avionics bus to the main bus.
%) The essential avionics relay is de-energized to connect the essential avionic bus to the
% essential bus.
% (14)ENGINE MASTER Switch % The ENGINE MASTER switch is located on the left, center of the instrument panel switch % panel. It has four sets of contacts. When set to ON, each set of contacts connects one input
% to one output as follows:
%) ECU Alt Pwr relay output to ECU B.
%) ECU A power supply to ECU A.
%) Alternator excitation battery to the alternator field connection.
%) ELECTRIC MASTER key switch START connection to the Starter relay.

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Section 24-30 % DC Generation - Lycoming Engine
1. General
% The DC generation system for the DA 40 with the Lycoming engine has these components: ) Alternator. ) ALT/BAT switch. ) Alternator control circuit-breaker. ) Alternator circuit-breaker. ) Voltage regulator. ) Alternator protection circuit-breaker.
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Electrical Power
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AVIONIC

VOLTAGE REGULATOR
MAIN BUS

BUS

Figure 1: DC Generation (simplified), Electrical System without Essential Bus
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2. Description and Operation
Figures 1 and 2 show simplified DC electrical generation schematic diagrams.
A. Alternator
A 70 ampère alternator attaches to the front of the engine. A flexible belt turns the alternator. A pulley on the engine crankshaft operates the flexible belt. The alternator is the usual source of power for the electrical system.
The output voltage from the alternator is controlled by the voltage regulator. The voltage regulator controls the output voltage at 28 V ± 2.5 %. The output from the alternator supplies the main electrical bus.
The alternator can supply 70 ampères continuously at engine speeds above 2100 RPM. The graph at Figure 3 shows the alternator performance.
The alternator has these connections:
AUX Cable Ident. 24015A20.
F1 Cable Ident. 24014A20.
+ Cable Ident. 24007A6
F2 Cable Ident. 24018A20N

The alternator will come on line when:
) The engine is operating.

) The battery, alternator control, alternator protection, alternator and voltage sense circuit-breakers are closed.
) The ALT/BAT switch is set to ON.
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AVIONIC
VOLTAGE REGULATOR MAIN BUS
BUS

Figure 2: DC Generation (simplified), Electrical System with Essential Bus
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B. Voltage Regulator
The voltage regulator is located in the engine bay. An in-line connector connects the voltage regulator to the main cable harness. The voltage regulator has these functions: ) Provides electrical protection for the alternator in the event of equipment failure. ) Operates a low voltage warning if the alternator voltage falls below 24 Volts. ) Operates a warning if the alternator fails or goes off line. ) Controls the output voltage of the alternator to the main electrical bus.
　
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