TM10-3930-660-34 CHAPTER 6 ELECTRICAL SYSTEM MAINTENANCE Section I.  DESCRIPTION AND DATA 6-1. GENERAL. This chapter covers maintenance procedures for the electrical system components, as well as principles of operation. 6-2. PRINCIPLES OF OPERATION. a. Charging System.  The charging system includes the alternator, rectifier and voltage regulator.  The rectifier and voltage regulator are integral with the alternator.  The basic function of the charging system is to maintain the vehicle battery voltage (charge) at the specified level.  The alternator is an ac generator that is belt-driven by the engine crankshaft pulley.  The ac produced in the alternator stator windings is converted to dc by action of a diode rectifier bridge.  The initial output from the alternator is made possible by residual magnetism in the rotor poles.  As the rotor turns, the magnetic lines of force produced by the residual magnetism cut through the stator windings and current flow is produced by the stator windings.  As engine speed increases, alternator rotor speed also increases. Current flow produced by the stator increases accordingly. A portion of the current produced in the stator windings is shunted through a diode trio to the field winding.  The diode trio converts the ac output of the stator windings to dc for application to the field winding.  Current flow through the field winding increases the strength of the magnetic field surrounding the rotor, and a resultant increase in stator current occurs.  Current flow in the field winding circuit is controlled electronically by the regulator.  The regulator, in effect, monitors battery voltage and switches on and off several times a second in normal operation to maintain the required battery voltage level. b. Starting Motor.  The function of the starting motor is to turn the engine flywheel at a fast enough rate to initiate engine combustion. An electric solenoid, activated by the START switch, pulls the starting motor drive pinion into engagement with the ring gear on the engine flywheel.  At the same time, movement of the solenoid closes a set of switch contacts which connect the starting motor armature to the battery through a set of four carbon brushes.  Current flow in the armature causes the armature to rotate.  The drive pinion then rotates and turns the engine flywheel.  When the engine starts, centrifugal force resulting from increased flywheel speed, moves the starting motor pinion out of engagement with the flywheel ring gear.  Releasing the START switch causes the solenoid to de-energize and disconnect the battery from the starting motor. 6-1