DC Electrical Load Distribution

The DC electrical load distribution selects the electrical power from the battery power, the main DC generation, and the external power, and distributes it to the helicopter systems. It consists of the Electrical Power System Unit (EPSU), circuit breaker panel, and 28 VDC receptacle.

Electrical Power System Unit (EPSU)

The EPSU consists of the power distribution unit and the Generator Control Unit (GCU) combined in one unit. It performs the functions that follow:

• Controls the application of battery power, external power, and starter generator power.

• Controls the cranking of the engine.

• Regulates the output of the starter generator and provides protection from over-voltage.

• Provides discrete signals to the integrated avionics unit and to the engine and airframe interface unit for monitoring the status and the parameters of the DC electrical load distribution system.

The EPSU is located in the right aft fuselage.

Circuit breaker panel

The circuit breaker panel distributes electrical power to every helicopter system and provides a central location for their circuit protection. It consists of the main bus and the system circuit breakers. It is located in the right aft fuselage.

28 VDC receptacle

The 28 VDC receptacle provides a convenient power source for equipment inside the cockpit. It is located in the center console.

Operation

The battery provides 25.5 VDC to the EPSU. The BATT switch commands the EPSU to apply the battery power to the helicopter systems.

The starter generator uses a single cable to carry the high current required for starting and to supply the generator output. This cable is connected to the STARTER GENERATOR connection of the EPSU. The GEN switch commands the EPSU to apply the generator power to the helicopter systems. The EPSU regulates the output voltage of the starter generator.

The external power receptacle provides power from an external source to the EPSU and commands its application to helicopter systems.

The EPSU provides the electrical power to the main bus through its LOAD connection. The circuit breaker panel distributes the electrical power to the helicopter systems through their respective circuit breakers.

The 28 VDC receptacle provides an electrical power outlet in the center console and can be isolated with the 28V AUX POWER.

The EPSU communicates the system status to the integrated avionics unit through the discrete connections that follow:

EPSU	Integrated avionics unit
GP STATUS	EXTERNAL POWER
BATTERY STATUS	BATTERY RELAY
EPSU FAILED	EPSU FAIL
GLC STATUS	GENERATOR DISCONNECTED
START INDICATOR	STARTER ON

The EPSU provides a voltage signal proportional to the starter generator output current on the SHUNT + and SHUNT - connections to the ANALOG/CURRENT MONITOR IN 1A HI and ANALOG/CURRENT MONITOR IN 1A LO connections respectively of the engine and airframe interface unit.

The engine and airframe interface unit measures the main bus voltage with its ANALOG IN 2A HI connection through the GEA circuit breaker and its ANALOG IN 2A LO connection to a ground connection.