ELECTRICAL I LESSON 3 CHARGING SYSTEM BASICS

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ELECTRICAL I LESSON 3
CHARGING SYSTEM BASICS

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  this lesson.

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The charging system has two functions

• Maintain the battery at a fully charged state.
• Provide current for all electrical loads while
  the engine is running.

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To keep the battery fully charged the charging
system must produce current at a voltage 1 to 2
volts above battery voltage.

• The charging system must produce more current
  than the accessory loads draw so it will have
  current to charge the battery.
• A battery in a discharged state will charge at a
  high current rate and a low voltage.
• As the batterys charge is restored, its voltage
  increases. Its voltage acts as CEMF.
• The charging voltage must increase to maintain
  current flow through the battery.
• The charging voltage is limited at about 2 volts
  above battery voltage to prevent battery
  overcharging.
• Charging current decreases as the battery
  recharges.

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Charging System Components

• Alternator or A.C. Generator
• Voltage Regulator
• Charge Indicator

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Alternator Construction and Operation

• An alternator or A.C. generator creates voltage
  by rotating a magnetic field inside a looped
  conductor.

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Alternator Components

• Rotor
• A multi-pole electromagnet that is rotated by a
  belt pulley. Usually 4 to 7 pole pairs.
• Rotor Components
• Winding Slip Rings
• Magnetic Pole Pieces
• Shaft With Iron Core
• Stator
• A circular laminated iron frame that holds the
  looped conductor.
• An automotive alternator stator usually has three
  separate looped conductors.
• Each conductor has as many loops as the rotor has
  pole pairs.
• The current output is 3-phase (3 over-lapping
  A.C. currents).
• Delco image InnerAuto image

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Stator Winding Types

• Wye (Y) - 3 looped conductors connected in
  series. Higher voltage output at low speeds.
  
• Delta - 3 looped conductors connected in
  parallel. Higher current output at low speeds.

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Rectifier Bridge

• A set of 6 or more diodes used to rectify the
  A.C. current in the stator into D.C. current
  before it leaves the alternator.
• The diodes are mounted in a heat sink.

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The Charging System consists of two circuits
Output and Field
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Output Circuit

• The output circuit consists of the stator
  windings, rectifier bridge, battery and all
  electrical loads.
• The stator produces current in two conductors
  during the same time period.
• As the rotor rotates, the stator windings that
  produces current change every 120 degrees. This
  produces 3-phase output.
• As the magnetic poles alternate past the loops
  they produce A.C. voltage.
• The rectifier bridge consists of positive diodes
  connected to (B) and negative diodes connected
  to (B-) in pairs.
• The stator output goes into the bridge as A.C.
  and leaves as D.C..

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Field Circuit

• The field circuit may consist of the rotor
  winding, slip rings brushes, voltage
  regulator, indicator bulb and wiring.
• The field circuit controls the current flow
  through the rotor winding.
• This current is called the excitation current.
  
• Excitation current is provided by the battery
  before the stator begins producing current.
• The stator provides excitation current after the
  alternator starts producing current.

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Voltage Regulator

• The voltage regulator is part of the field
  circuit.
• It limits alternator output voltage by
  controlling the strength of the rotor field.
• The regulator senses battery voltage and controls
  system voltage to a safe level by pulsing the
  rotor current.
• Long pulses result in a stronger field and higher
  voltage output and vice versa.
• Maximum alternator current output is limited by
  stator CEMF.
• Output voltage will exceed 16V if not regulated.

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Field Circuit Types

• A
• The regulator supplies the ground for the field
  circuit. The other side of the field is
  connected directly to battery B().
• Both brushes are insulated.
• A for after rotor!
• B
• The regulator supplies B() for the field
  circuit.
• One brush is insulated, the other is grounded.
• B for before rotor!
• Isolated
• The ignition switch supplies B() to the field.
• The regulator supplies the ground. Both
  brushes are insulated.

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Type A Field circuit current flows

• Click on one of the following to view an
  animation of the current flow path.
• Initial KOEO
• Excitation KOEO
• Excitation KOER

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Type B Field circuit current flows

• Click on one of the following to view an
  animation of the current flow path.
• Initial KOEO
• Excitation KOEO
• Excitation KOER

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Type Isolated Field circuit current flows

• Click on one of the following to view an
  animation of the current flow path.
• Initial KOEO
• Excitation KOEO
• Excitation KOER

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Charge Indicators

• Ammeter -
• Connected between the battery and all other
  electrical components.
• Shows amount of current flowing into and out of
  the battery.
• Charge indicates the alternator is charging the
  battery.
• Discharge indicates the battery is supplying
  current for the loads.
• Diagrams Generic Ford w/shunt
• Voltmeter -
• Indicates charging system voltage output.
• Indicator Light -
• The voltage regulator turns the light on if the
  stator output drops to zero volts or over 16
  volts in some cases.

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Charging System Testing
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Alternator Output

• Measure current output at the alternator B()
  wire while loaded to 12V at 2000rpm.
• Should be within 10 of rated output.
• Example Alternator rating 120 amps
  Tested output should be
  0.9 x 120 amps 108
  amps minimum

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Battery Charging Current

• Measure current at the battery while loaded to
  12v at 2000 rpm.
• Should be within 20 amps of alternator tested
  output.
• Example Alternator tested output 115 amps
  Tested current should be
  115 amps - 20
  amps 95 amps minimum

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Full-field Charge Current

• Bypass the regulator and measure battery charging
  current.
• Do this test only if both of the above fail.
• If the alternator now charges the regulator is
  probably at fault.

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Output Circuit Voltage Drop

• Tests for high resistance in the output circuit.
  
• Measure voltage drop with the battery charging
  current at or above 25 amps.
• See Charging System Test procedure sheet

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Field Circuit Test

• Check for proper available voltage to all field
  circuit terminals at the alternator and
  regulator.
• Check all grounds!
• Always check the circuit wiring before condemning
  the alternator or regulator!!!

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Regulator Voltage

• Measure battery voltage when the battery charging
  current is 10 amps or less.
• Should be 13.5v to 15v

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Diode A.C. Ripple

• Checks the condition of the rectifier bridge
  diodes.
• Should be less than 0.5vac with DMM.
• Should be less than 400mv below 0v with scope.
• Examples Good a.c. Bad a.c. Good d.c. Bad
  d.c.