DA 40 Series

%  (5) ECU Bus 
%  The ECU bus is located at the left end of the circuit breakers. The ECU bus has power when 
%  the any one of the following are connected to the relay junction box bus: 
%  ) The main battery. 
%  ) External power. 
%  ) The alternator. 
%  The ECU bus provides power for Engine Control Unit A (ECU A) and ECU B. A 25 A circuit-
%  breaker protects each circuit. 
%  It also provides power for the ECU alternate power relay (ECU Alt Pwr relay), for the essential 
%  tie relay, and for the power relay. 
%  During the usual operation, 12 V from the ECU bus energizes the ECU Alt Pwr relay. One set 
%  of contacts close to connect the ECU B supply through the ENGINE MASTER switch to the 
%  ECU. The second set of contacts close to provide charging current for the ECU backup battery. 
%  A resistor in the circuit limits the charging current. A diode prevents the battery from 
%  discharging through the circuit. 
%  If power to the ECU bus fails, the ECU Alt Pwr relay de-energizes. The contacts open to break 
%  the supply from the ECU bus and connect the ECU backup battery. The second set of contacts 
%  open to break the charging circuit. 
% 
%  (6) Main Bus 
%  The main bus provides power for the consumers. Each consumer has a circuit breaker to 
%  protect the circuit. The main bus also connects to the switch contacts of 3 relays: 
%  ) The starter relay. 
%  ) The avionics master relay. 
%  ) The essential tie relay. 
%  A circuit-breaker protects the supply to each relay. 
% 

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AMM

% (7) Power Relay.
% The power relay connects the relay junction box bus and ECU bus to the main bus. The % essential bus switch controls the power relay.
% (8) Essential Tie Relay.
% In the usual (de-energized) condition, the essential tie relay connects the main bus to the % essential bus.
% In the emergency (energized) condition, the essential tie relay connects the hot battery bus to % the essential bus.
% The essential bus switch controls the essential tie relay.
% (9) Essential Bus Switch (marked ESS BUS).
% The ESS BUS switch is located in the switch panel at the bottom left of the instrument panel.
% In the OFF position, the ESS BUS switch gives a ground to the power relay coil. The relay % closes and connects the relay junction box bus to the main bus. This is the usual position when % all systems are operating correctly.
% In the ON position, the ESS BUS switch disconnects the ground from the Power relay coil. The % Power relay opens and disconnects the main bus from the power supply (the relay junction box % bus). It also gives a ground to the coil of the essential tie relay. The relay energizes to break % the connection between the main bus and the essential bus. At the same time, it connects the % hot battery bus to the essential bus.
% There is a light emitting diode in the essential bus switch. If there is power on the hot battery % bus, and the ELECTRIC MASTER key switch is set to ON or START, the light emitting diode % comes ON.
% (10)Starter Relay.
% The Starter relay contacts and coil connect to the main bus. A 10 A circuit-breaker protects the % circuit.
% When the ENGINE MASTER switch set to ON and the ELECTRIC MASTER key switch is set % to START, they give a ground to the relay coil. The relay connects the main bus to the starter % solenoid (part of the starter). The solenoid engages the starter and operates a heavy-current % contactor to connect the relay junction box bus to the starter.
　
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