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Battery
Relay
RL1
Starter
Relay
Ref DA4-9274-00-01
24404A22
24403A6
24405A6N
EPU
Connector
GSFW
24020A4
B1
28 VDC Battery
GSFW
ENGINE COMPARTMENT
FIRE WALL
Figure 1: External Power System Schematic Diagram
AIRCRAFT
DA 40 Series
AMM
Electrical Power
Doc # 6.02.01
Rev. 5 24-40-00 Page 3
20 Sep 2007
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.
AIRCRAFT
Electrical Power DA 40 Series
AMM
Page 4
20 Sep 2007 24-40-00 Doc # 6.02.01
Rev. 5
Intentionally left blank
AIRCRAFT
DA 40 Series
AMM
Electrical Power
Doc # 6.02.01
Rev. 5 24-40-00 Page 101
20 Sep 2007
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.
AIRCRAFT
Electrical Power DA 40 Series
AMM
Page 102
20 Sep 2007 24-40-00 Doc # 6.02.01
Rev. 5
Intentionally left blank
AIRCRAFT
DA 40 Series
AMM
Electrical Power
Doc # 6.02.01
Rev. 5 24-40-00 Page 201
20 Sep 2007
Maintenance Practices
1. General
This Section tells you how to remove/install the external power relay. Refer to the component
manufacturers manuals for more data and shop data.
2. Electrical Safety
The DA 40 has a low voltage DC electrical system. When correctly maintained it is safe to work on.
The battery can supply heavy current through low resistance circuits (for example, if you ground the
positive output with a wrench by accident).
Always follow the usual safety practices for working on electrical equipment. Allow only qualified
persons to maintain the electrical system.
CAUTION: DISCONNECT THE BATTERY BEFORE DOING MAINTENANCE ON
THE ELECTRICAL SYSTEM. MAKE SURE THAT YOU DISCONNECT
THE NEGATIVE LEAD FIRST.
CAUTION: AFTER DOING ELECTRICAL MAINTENANCE ALWAYS DO A
CONFIDENCE TEST OF THE SYSTEM WITH A 24 VOLT POWER
SUPPLY THAT HAS OVER-CURRENT PROTECTION. DO THIS
BEFORE CONNECTING THE BATTERY
CAUTION: USE ONLY DA 40 SPARE PARTS APPROVED BY THE
MANUFACTURER.
3. Remove/Install the External Power Relay
A. Remove the External Power Relay
Detail Steps/Work Items Key Items/References
(1) Remove the engine cowlings. Refer to Section 71-10.
(2) Disconnect the battery:
S Disconnect the negative cable from the
battery.
S Disconnect the positive cable from the
battery.
(3) Remove the cover from the relay box.
AIRCRAFT
Electrical Power DA 40 Series
AMM
Detail Steps/Work Items Key Items/References
Page 202
20 Sep 2007 24-40-00 Doc # 6.02.01
Rev. 5
(4) Disconnect the electrical cables from the external
power relay.
(5) Remove the 2 bolts which attach the external
power relay to the relay box.
(6) Move the relay clear of the airplane.
B. Install the External Power Relay
Detail Steps/Work Items Key Items/References
(1) Put the relay in position in the relay box.
(2) Install the 2 attaching bolts.
(3) Connect the power and control cables to the
external power relay.
Refer to Chapter 92 for the wiring
diagrams.
(4) Install the cover to the relay box.
(5) Connect the positive cable to the battery. Apply Dow Corning compound (DC4)
to the battery terminal and the cable
lug.
(6) Connect the negative cable to the battery. Apply Dow Corning compound (DC4)
to the battery terminal and the cable
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