Technical data

13773-001
24-40
Page 1
EXTERNAL POWER
1. DESCRIPTION
The external power connector is mounted on the Master Control Unit (MCU). The MCU is mounted on
the left side of the fuselage, just forward of the firewall. The receptacle is comprised of a three-contact
connector. The long contacts are used for transferring power. The shorter, third connector, engages
the external power relay located in the MCU, which connects the external power to the Main Distribu-
tion Bus. By making this contact shorter, power will not be transferred until a reliable connection is
made between the jack and plug, thereby reducing the chance of arcing or sparking. In addition, the
signal power to the relay contains an isolation diode to prevent reverse polarity. If reverse polarity is
applied to the external power connector, the relay will not engage, preventing connection of the exter-
nal source to the primary bus.
The external power receptacle is installed to permit the use of an external power source for cold
weather starting and maintenance procedures requiring reliable power for an extended period. The
external power source must be regulated to 28 VDC. The external power control contactor is wired
through the BAT 1 switch so that the BAT 1 switch must be on to apply external power.
2. MAINTENANCE PRACTICES
A. External Power Receptacle
Because the external power receptacle is part of the MCU, the MCU must be replaced if the receptacle
were to fail.
(1) Removal - Refer to MCU removal. (Refer to 24-30)
(2) Installation - Refer to MCU removal. (Refer to 24-30)
30 Nov 2000