Charging system and starting system

(a) Alternator and charging system

The alternator supplies the electrical loads and recharges the battery while the engine runs. It is preferred to a DC generator because it gives output even at idle, is light and has no commutator.

 Rotor (field winding, slip rings) in stator (3-phase winding)
 Stator -> 6-diode rectifier -> B+ (battery, loads)
 Voltage regulator -> controls field current

• Rotor: a claw-pole electromagnet whose field winding is fed through slip rings and brushes; it is driven by the engine belt.
• Stator: a fixed three-phase winding in a laminated core, in which AC is induced as the rotor field cuts the conductors.
• Rectifier: six silicon diodes change the AC to DC.
• Voltage regulator: senses the system voltage and varies the field current (by switching) to keep the output at 13.8 to 14.4 V at any speed and load. Without it, the output would rise with speed, since the induced emf depends on speed and field strength.
• A charge-warning lamp lights when the alternator is not charging.

(b) Starting system

 Battery -> Ignition switch -> Solenoid -> Starter motor
                                |-> shift lever -> pinion -> flywheel ring gear

• Starter motor: a series-wound DC motor that gives very high torque at low speed, drawing about 150 to 300 A.
• Solenoid (magnetic switch): when the key is turned, the solenoid pulls its plunger. This closes the heavy contacts that feed the motor and moves the shift lever, which pushes the pinion into mesh with the flywheel ring gear (pre-engaged drive). In the older inertia (Bendix) drive, the pinion is thrown into mesh by its own inertia instead of by a lever.
• Overrunning clutch: lets the pinion transmit torque to the engine, but frees it once the engine starts, so the armature is not over-speeded.
• The gear ratio between the ring gear and the pinion is about 10:1 to 15:1.

A starter relay and a neutral safety switch may also be in the circuit.