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Chapter 33

Chapter 33. Charging System Fundamentals. Contents. Basic charging system parts Charging system functions Types of charging systems Alternator operation Alternator construction Charge indicators. Basic Charging System Parts. Charging System Parts. Alternator

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Chapter 33

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  1. Chapter 33 Charging System Fundamentals

  2. Contents • Basic charging system parts • Charging system functions • Types of charging systems • Alternator operation • Alternator construction • Charge indicators

  3. Basic Charging System Parts

  4. Charging System Parts • Alternator • generator that uses mechanical power to produce electricity • Usually have a preset output voltage of 13.5-14.75 volts DC • Voltage regulator • controls the output voltage of the alternator • Alternator drive belt • links the engine crankshaft pulley with the alternator pulley • engine crankshaft pulley drives the alternator belt

  5. Charging System Parts • Charge Indicator • ammeter, voltmeter, or warning light • informs driver of the charging system condition • Harness • wiring connecting the parts together into asystem • Battery • provides current to start the vehicle • provides current to initially energize the alternator field • stabilizes the alternator output

  6. Charging System Recharges the battery and supplies electricity when the engine is running

  7. Charging System Functions • Recharges the battery after cranking • Supplies the car’s electricity when the engine is running • Provides an output voltage slightly higher than the battery voltage • Changes the output to meet varying loads

  8. Types of Charging Systems • Two types: • DC generator • AC generator (alternator)

  9. DC Generator • Similar to an electric motor • Stationary magnetic field • The output conductor unit (armature) spins inside the field • Induces current from within the armature

  10. AC Generator (Alternator) • Advantages: • more efficient • smaller and lighter • more dependable • more output at idle

  11. AC Generator (Alternator) Theory • The magnetic field rotates • The output conductors (windings) are stationary • The field rotates, inducing current in the output windings • Alternators are constructed in reverse of a DC Generator

  12. Generator versus Alternator

  13. Alternator Operation • Two main parts, rotor and stator • The rotor is located in the center • creates a rotating magnetic field when turned by the drive belt • The stator is a stationary set of windings surrounding the rotor • output winding in the alternator

  14. Alternator Operation • When the rotor spins, its strong magnetic field cuts across the stator windings • Current is induced in the stator windings

  15. Alternator Operation

  16. AC Output • Alternating current flows one way, then the other • As the rotor turns into one stator winding, current is induced • When the same rotor pole moves into the other stator winding, the current reverses direction

  17. Rectified AC Current • An automobile’s electrical system requires direct current (DC), which flows one way • Alternator output must be rectified (changed) from AC to DC • A diode allows current flow in only one direction • Several diodes are connected into a rectifier circuit

  18. Diode Acts as a one-way electrical check valve

  19. Diode Operation

  20. Alternator Construction

  21. Rotor • Field windings mounted on a shaft • Two claw-shaped pole pieces surround the windings, increasing magnetic field • The fingers on one pole piece produce south magnetic poles • The fingers on the other pole piece produce north magnetic poles

  22. Rotor Operation As the rotor spins, alternating polarity produces alternating current

  23. Slip Rings • Mounted on the rotor shaft • Provide current to the rotor windings • An external source of electricity is needed to excite the field

  24. Brushes • Ride on the slip rings • Provide a sliding electrical connection • Feed battery current into the slip rings and rotor windings • Small coil springs hold the brushes in contact with the slip rings

  25. Brushes and Slip Rings

  26. Anti-Friction Bearings • Two types of anti-friction bearings are used in typical alternator construction • Pre-lubricated sealed ball bearings • Oil-impregnated bronze bushings

  27. Rectifier • Six diodes (2 diode trios) convert stator output to direct current • Provides full-wave rectification • Changes both positive and negative outputs into direct current • Diode trio may be used to feed power from the stator to the field windings (rotor)

  28. Charging Circuit

  29. Stator • Three groups of windings wrapped around a soft, laminated iron core (ring) • Produces an electrical output • The iron core concentrates the field around the windings

  30. Stator and Rectifier A rectifier consists of six diodes connected to the stator windings

  31. Alternator Fan • Mounted on the front of the rotor shaft • Draws air through and over the alternator • Cools the windings and diodes

  32. Pulley and Belt The crankshaft drives the alternator belt

  33. Types of Belts

  34. Voltage Regulator • Controls the alternator output voltage • Changes the amount of current flowing through the rotor windings • The engine control module (ECM or PCM) may serve as the voltage regulator • The three types of voltage regulators are:internal, external, and computercontrolled

  35. Internally Regulated Alternator

  36. Voltage Regulators

  37. Electronic Voltage Regulator Operation • To increase the alternator output, the regulator allows more current into the rotor windings • The magnetic field around the rotor is increased • More current is induced in the stator windings, increasing output

  38. Battery Thermistor • Measures battery temperature • Allows the charging system to alter output as needed • A cold battery requires more voltage for charging than a hot battery • Often mounted on the positive battery cable

  39. Computer Monitor and Control • The powertrain control module (PCM) can supplement or replace the voltage regulator • The PCM can react to changing operating conditions • shuts the alternator off at wide-open throttle for better acceleration • more accurately controls the charge rate, allowing a smaller, lighter battery • Switches on and off 400 cycles per second

  40. Charging System Internally regulated alternator

  41. Charging System Note computer monitoring and battery thermistor

  42. Charging System The PCM contains the regulator circuit

  43. PCM Control Advantages • Disconnects the alternator output if voltage levels become too high, thereby protecting the on-board electronics • More accurately controls output voltage • Disconnects alternator output under full throttle conditions allowing for better acceleration

  44. Charge Indicators • Informs the driver of the operating condition or output of the charging system • Types: • warning light • voltmeter indicator • ammeter indicator

  45. Charging Circuit The warning light illuminates when the alternator output drops below a specified voltage

  46. Voltmeter Indicator • A battery has 12.6 volts when fully charged • Alternator output must be higher: • 13–14.75 volts • A voltmeter shows the voltage

  47. Ammeter Indicator • Shows the current output in amperes • Reads to the right if the battery is being charged • Reads to the left if the battery is discharging

  48. Charging Circuit Basic connections for an ammeter indicator

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