4-1 ARMY TM 5-6115-612-34 MARINE CORPS TM 6115-34/8 AIR FORCE TO 35C2-3-471-2 NAVY AG-320BO-MME-OOO CHAPTER 4 MAINTENANCE OF DC ELECTRICAL AND CONTROL SYSTEM 4-1. PURPOSE  AND  FUNCTION  OF  DC ELECTRICAL AND CONTROL SYSTEM. This section gives a functional description and maintenance procedures for the DC electrical and control system. The system consists of the battery cable, battery, wiring harness (W1), slave receptacle, generator electronic control  module  (GECM),  circuit  breaker, starter, and 20 amp current shunt. a. Purpose. The DC electrical and control system provides turbine rotation during startup, generator output control and sensing, generator protection, and battery charging. b. Functional  Description. The following  is  a  simplified  functional description of the DC electrical and control  system. The description is keyed to the schematic in FO-5, TM 5-6115-612-12. (1)  Startup. When startup  is begun, 24 volts from the battery are applied through the DC CIRCUIT BREAKER (CB1) to the MASTER SWITCH. When the MASTER SWITCH is placed in the RUN position, the transfer pump will come on and fill fuel filters. When the switch  is  placed  in  the  START  position, the 24V signal is connected to the engine  electronic  control  module  (EECM) on  the  start  circuit. If the EECM has not detected any faults in the generator  set, it outputs the start enable signal to the starter solenoid. The  solenoid  energizes,  supplies  24 volts to  the starter motor, and repositions the   actuator.   As the starter motor begins to turn, the actuator  causes  the  starter  gear  to mesh with the turbine flywheel. Turbine speed is sensed by the digital speed sensor and relayed to the EECM. When turbine speed reaches 60 percent of maximum, the EECM interrupts the start enable power. The solenoid removes power from the starter and retracts the starter gear from the turbine  flywheel. (2) Generator Output Control and Sensing. generator field-winding power and provide overtemperature protection. These functions are controlled and monitored by the GECM and the EECM. If the EECM does not sense a fault in the generator  set, it enables the GECM via the enable circuit on J4 pin F to the GECM J2 pin L. The GECM senses the temperature of the generator field winding at J1 pin F. If the temp- erature is normal or below, field winding  power is switched onto the field positive (+) and negative (-) lines (J1 pins C and B) to the gen- erator. The amount of field winding power is adjusted by the GECM to main- tain the output voltage level set by the VOLTAGE ADJUST knob. The GECM compares the output voltage setting at J2 pin R with the remote voltage sense at J2 pins E and F. If the two inputs are different, circuitry in the GECM adjusts the field power until the output voltage is correct. (3) Generator Protection. The generator is protected from over- temperature, overvoltage, under- voltage, and overloading. If  any condition exceeds programmed limits, the GECM interrupts the field current and sends a fault signal to the EECM. When the EECM detects a fault, it turns on the appropriate MALFUNCTION indicator  light and starts engine shutdown. The EECM will not permit startup until the malfunction has been corrected. Each of these  conditions is  described  below.