DC Generation

The DC generation provides the electrical power needed for starting and for normal operation of the helicopter. The stored electrical power is used to produce the high amount of current needed to start the engine. During normal operation, the electrical power used for starting the engine is replenished, ensuring that sufficient electrical power is always available. It also has a means of shutting off the electrical power to prevent it from being drained.

The DC generation is monitored by the Integrated Avionics System (IAS). It consists of the components that follow:

• Starter generator

• GEN switch

• Power feeder

• Battery

• BATT switch

Starter generator

The starter generator combines the starter and generator functions in one unit to save weight. It is located in front of the engine on the Reduction Gear Box (RGB). It is attached with a V-band clamp via the Quick Attach-Detach (QAD). It is a shunt start type that reduces the number of connections needed as the same heavy gauge cable used to supply the high current for starting is also used for output of the generated electrical power. Its body consists of the drive end bell at the forward end which has a flange to mount it to the QAD, a screen for cooling air output, and a bearing. The stator is contained inside the main body and the rotor rotates inside it. The terminal block is mounted on the body and provides connections to the helicopter systems. The aft end consists of the cooling duct assembly which contains the commutator end bell, the brushes, a bearing, and the fan assembly. The rotor of the starter generator is mechanically linked to the engine through the RGB.

The starter generator initially cranks the engine and after starting generates electricity. The Electrical Power System Unit (EPSU) controls the switching between cranking and generating modes of operation, and the regulation of electricity generation. Refer to DC Electrical Load Distribution.

GEN switch

The GEN switch is a Double-Pole, Double-Throw (DPDT) switch. It is located on the miscellaneous control panel. Refer to Instrument and Control Panels. It controls, through the EPSU, the generation of electricity by connecting and disconnecting the starter generator from the main bus and the battery.

Power feeder

The power feeder is an isolated pass-through heavy-duty connector. It is located on the right side of the forward firewall. It lets the high starting current and the generated electricity go through the forward firewall with minimal losses while keeping the integrity of this one.

Battery

The battery is an advanced, light weight, lithium-ion type. It stores enough electrical power to crank the starter and supply surges when needed during normal operation of the helicopter. It is located on the avionics shelf in the aft-center fuselage. It has a nominal voltage of 25.5 VDC and is rated at 17 amp-hour. It can provide a peak current of up to 840 amps for starting. It weighs 15.6 pounds (7.1 kg). Internal circuits monitor its state through a connection to the engine and airframe interface unit (GEA), and control its internal heaters and protection functions. Refer to General Computers. The battery has a vent to evacuate gaseous emissions if they are ever produced.

BATT switch

The BATT switch is a Single-Pole, Double-Throw (SPDT) switch. It is located on the miscellaneous control panel. It controls, through the EPSU, the application of the battery power to the helicopter systems.

Operation

The BATT switch provides a ground to the BATTERY ON connection of the EPSU for the control of the battery power.

The BATTERY STATUS connection of the EPSU to the BATTERY RELAY STATUS connection of the integrated avionics unit (GIA) informs the IAS when the battery is connected.

The positive terminal of the battery is connected to the BATTERY connection of the EPSU through a heavy gauge cable.

The EPSU applies the battery power to the main bus to feed the helicopter systems.

The negative terminal of the battery is connected to the helicopter structure through a heavy gauge cable and uses it for the return of the high current.

The status of the battery is monitored by the Integrated Avionics System (IAS) through the FAULT, HEATER, and CHARGE connections of battery to the BATT FAULT, BATT HEATER, and BATT CHARGE connections of the engine and airframe interface unit (GEA), respectively.

The temperature of the battery is monitored by the IAS through the RTD 1 PIN 1 and RTD 1 PIN 2 connections of the battery to the ANALOG IN 1 HI, ANALOG IN 1 LO-SIGNAL GROUND connections of the engine and airframe interface unit (GEA), respectively. The Resistance Temperature Device (RTD) inside the battery (2435BT1) has a positive temperature coefficient: resistance increases when temperature increases and it decreases when temperature decreases, it has a value of 100Ω at 0ºC (32ºF). The engine and airframe interface unit provides a small constant current to the RTD to measure its resistance.

Electrical power can also be provided by the external power connector. Refer to External Power.

The cranking system, through the engine switch and the start relay, controls the application of electrical power to the STARTER GENERATOR connection of the EPSU . The electrical power goes through the heavy gauge cable and the power feeder, and supplies the high current required for cranking to the B+ connection of the starter generator. Refer to Engine Control.

The START INDICATOR connection of the EPSU to the STARTER ON connection of the integrated avionics unit (GIA) informs the IAS that the starter generator is cranking.

The E- connection of the starter generator is used as return for the high current through a heavy gauge cable and the helicopter structure.

The starter generator cranks the engine through the mechanical link of its rotor to the RGB with the stator being rigidly held by the QAD.

The cranking system controls the EPSU to remove the electrical power from the STARTER GENERATOR connection. Refer to Engine Control.

The starter generator continues rotating through the mechanical link to the engine once the start cycle is complete.

The fan draws air in through the screen of the cooling duct assembly. This air is forced on the rotor and stator to cool them. The air exits through the screen at the QAD end of the starter generator.

The GLC STATUS connection of the EPSU to the GENERATOR DISCONNECTED connection of the integrated avionics unit (GIA) informs the IAS that the starter generator does not supply electrical power to the helicopter systems.

The GEN switch provides a ground to the GENERATOR CONTROL connection of the EPSU when it is in the GEN position. This controls the application of the STARTER GENERATOR connection of the EPSU to the main bus and to the battery. Refer to DC Electrical Load Distribution.

The EPSU provides a Pulse Width Modulation (PWM) signal to the A+ connection of the starter generator to regulate the generated electricity.

The regulated electricity from the starter generator is output on its B+ connection and follows the path of the cranking current in reverse to the helicopter systems.