Detail Steps/Work Items  Key Items/References 
(1)  Set the ELECTRIC MASTER key switch to ON. 
(2)  Set the ENGINE MASTER switch to ON.  The voltmeter must indicate the battery voltage. 
WARNING: MAKE SURE THAT THE AREA OF THE PROPELLER IS CLEAR BEFORE YOU OPERATE THE STARTER MOTOR. PROPELLERS CAN CAUSE INJURY OR DEATH. 
(3)  Operate the starter motor.  You do not have to start the engine. 
(4)  Set the ENGINE MASTER switch to OFF. 
(5)  Set the ELECTRIC MASTER key switch to OFF. 

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Section 24-40 % External Power - Lycoming Engine
1. General
The DA 40 has an external power socket located on the right side of the fuselage, near the battery. It is a standard 28 Volt DC power socket. When you connect external power to the external power socket, the external power control relay is energized and the external power comes on-line.
2. Description and Operation
Figure 1 shows a simple schematic diagram of the external power system. The external power system has these components:
A. 28 Volt Socket
The 28 VDC power socket is located on the right side of the fuselage, near the airplane battery. The socket has 3 pins:
) A large negative pin.
) A large positive pin.
) A small positive pin.
A diode connected between the small positive pin and the external power relay solenoid protects the system from reverse polarity.
B. External Power Relay
The external power relay is located in the relay box mounted on the firewall. Heavy duty cable connects the large positive pin to the input terminal of the relay. Another heavy duty cable connects the large negative pin to a ground point.
The small positive pin connects to the solenoid of the external power relay via the diode.
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FIRE WALL
RL3

EPU Connector

B1

GSFW

Figure 1: External Power System Schematic Diagram
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3. Operation
When you connect a 28 V DC power supply to the external power socket these things happen:
) Current can flow from the small positive pin to the solenoid, the solenoid operates and closes the relay.
) Current can flow from the large positive pin through the external power relay to the main bus or, if installed, to the essential bus.
) The large negative pin is connected to ground.
If the polarity of the power supply is incorrect, then the diode will prevent current from flowing through the solenoid. The solenoid will not operate and current cannot flow through the external power relay to the main bus or the essential bus.
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Trouble-Shooting
1. General
The table below lists the defects you could have with the external power system. If you have the trouble detailed in the Trouble column read across to the Possible Cause column. Then do the repair given in the Repair column.
Trouble  Possible Cause  Repair 
External power will not come on line.  No external power. External power relay is defective.  Make sure that the external power plug is securely in the socket. Make sure that the external power is operating correctly. Do a test of the external power relay, if necessary, replace the external power relay. 

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Maintenance Practices
　
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