1. Topics covered in this presentation:
Charging Systems
Topics covered in this presentation:
Charging System Components and Operation
Alternator Construction and Operation

2. The Function of the Charging System
Functions only when engine is running.
The charging system:
Charges the battery.
Generator
Supplies power to all electrical systems.
Alternator
Early vehicles used DC generators. Electricity was generated by a rotor spinning within a magnetic field (opposite of a DC motor).
Modern vehicles use alternators. Electricity is generated in the stationary stator windings by a spinning magnet (rotor with an energized field winding and iron finger poles).
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3. Basic Charging System Components
Typical components are:
Drive belt
Alternator
Battery
Charge
warning
lamp
The Alternator: Uses mechanical power to produce electricity.
Alternator Drive Belt: Drives alternator from crankshaft.
Charge Warning Lamp: Displays charging system information.
The Battery: Supplies voltage to alternator.
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4. Alternator and engine running
Charging System Operation
Drive belt
Crankshaft pulley
Alternator pulley
Alternator and engine running
Load
Current flow
volts
Battery
Engine off, battery supplies electricity to systems.
Engine running, charging system supplies electricity to systems.
The alternator is driven from the crankshaft pulley.
Its output voltage varies between 13 and 15 volts.
This is sufficient to charge the battery.
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5. The Alternator (External Side View)
Drive pulley
Output terminal B+
Regulator, rectifier and brush cover
End frame cover
Mounting ear
Drive frame cover
Circulation vents
Cooling fan
Typical alternator construction:
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6. The Alternator (External Rear View)
Typical rear terminals:
B+ terminal: Alternator output
Connector containing:
IG terminal: Voltage in from ignition switch to power alternator
S terminal: Senses charging voltage
L terminal: used by regulator to ground warning lamp
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7. The Alternator (Internal View)
Drive pulley
End cover
Slip ring end housing
Retainer nut
Casing retainer bolts
Typical components are:
Rectifier assembly
The rotor: Rotating field winding.
Voltage regulator
The stator: Stationary induction winding.
Rectifier assembly: Diode rectifier bridge.
Stator
Voltage regulator: Regulates output voltage.
Rotor
Cooling fans: Provide air circulation.
Cooling fans
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8. Alternator Components - The Rotor
Iron, claw-shaped, finger pole pieces
Typical rotor components:
Brushes
The field winding is wound over an iron core.
The finger poles surround the field winding.
The field winding is attached to the slip rings.
Field winding
Slip rings
Main shaft
The brushes transfer voltage to the slip rings.
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9. Rotor Magnetic Field
When voltage is applied to the field winding, a magnetic field is created.
It saturates the finger poles, creating north and south poles.
Stator windings
Curved flux lines
Voltage in
North and south poles
As the rotor turns, alternating north and south magnetic fields are created.
Magnetic field strength = current flow + closeness of finger poles.
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10. Alternator Components - The Stator
The stator has 3 sets of evenly spaced windings.
Stator
Enamel copper
wire windings
They are held within a frame of soft iron laminations.
3 outputs
The windings are interlaced to produce AC voltages that are 120° apart.
Output voltage depends upon rotor speed and its magnetic field strength.
Soft iron lamination
The windings connect to a diode rectifier bridge.
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11. Single Phase Voltage Induction+ -
Single winding (stator).
Magnet (rotor).
When magnet rotates, it induces voltage in the winding.
Winding
Magnetic field
Rotor
Maximum voltage = when winding is cut by maximum flux.
Occurs when magnet is at 90° to winding.
When magnetic field direction changes, induced voltage polarity is reversed.
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12. Three Phase Voltage Induction
The stator has 3 windings, that are 120° apart.
As the magnet rotates, it induces voltages in all 3 windings.
The voltages produce a stable 3 phase output, ready for DC conversion (rectification). + -
120°
180
360
The windings are connected in either Star or Delta configurations.
Star
Delta
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13. Rectification Diodes allow current to flow in only one direction.
Anode
Cathode + -
Diodes allow current to flow in only one direction.
Output
Diode AC
voltage
Battery
emf + -
They conduct when a forward voltage is applied to the anode.
In this case, the positive part of an AC voltage.
Output AC
voltage D1 D4 D2 D3
Battery
emf + -
If 4 diodes are connected to make a bridge, current can flow during positive and negative parts of the AC voltage, producing a totally positive (DC) output.
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14. Alternator Components - The Rectifier Bridge
‘B’ terminal
Negative diodes
Stator terminals
Positive diodes
Converts 3 phase AC voltage into DC voltage.
The bridge is constructed using 6 diodes.
3 are used on the positive side of the bridge and 3 are used on the negative side.
The diodes are mounted on a heat sink.
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15. Three Phase Rectification
Two diodes are connected to each stator winding.
The rectification process creates 3 positive voltages.
Stator output
Rectifier output
They are added together to form a DC voltage that has a small ripple.
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16. Basic Three Phase Rectifier Operation
Rotor at winding 1, induced voltage is applied to battery +, via D1. + -
Return path from battery - is via D5 and D6 to windings 2 and 3.
Rotor at winding 2, induced voltage is applied to battery +, via D3.
Return path from battery - is via D4 and D5 to windings 1 and 3.
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17. Rotor Field Excitation
The rotor requires voltage to produce a magnetic field.
Engine stopped, ignition on, battery voltage is applied to rotor, via charge warning lamp.
Lamp is on and current flows through rotor winding.
Engine running, alternator speed increases, voltage output also increases.
Alternator voltage > battery voltage = lamp out, battery being charged = alternator current flowing through rotor, via field diodes.
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18. Alternator Components - Voltage Regulator
Rotor field winding voltage must be regulated to maintain alternator output at specified voltage level.
The voltage regulator senses alternator output and changes field winding current.
Output voltage < specified, regulator increases field winding current, output voltage increases.
Output voltage > specified, regulator decreases field winding current, output voltage decreases.
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19. Other Alternator Components
The carbon brushes supply voltage to the rotor winding, via two slip rings.
The slip rings connect the rotating field winding to the carbon brushes.
The drive pulley is fitted to the end of the rotor shaft and driven by a belt, from the crankshaft.
The cooling fans provide air to cool alternator components.
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