Download Charging System Fundamentals

Charging System
Fundamentals
Chapter 30
© 2012 Delmar, Cengage Learning
Objectives
• Explain electrical generation principles
• Describe AC generator parts
• Explain the operation of a voltage regulator
© 2012 Delmar, Cengage Learning
Introduction
• Charging system
– Important part of electrical system
– Allows battery to maintain charge and operate
accessories
© 2012 Delmar, Cengage Learning
Charging System
• Charging system components
– Alternator and voltage regulator
– Dash light or gauge
– Related wiring
• Charging replenishes the battery
– Output increased when load causes battery
voltage to drop
• Starter motor is a large load on the battery
– AC generator recharges battery and supplies
electrical needs
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Direct Current (DC) Generators
• Older cars used DC generators
– Produces AC
• Output is DC because its commutator has brushes
on north and south poles
• Drawbacks
–
–
–
–
More current must flow through brushes
Brushes wear out
Speed limited to 10,000 rpm
Do not produce enough output at slow speeds to
supply electrical accessories
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
AC Generator/Alternator
• Alternator is an AC
generator
– Electromagnet
passes across wire
to induce voltage
• Stator: stationary
conductor
• Rotor: rotating
electromagnetic field
© 2012 Delmar, Cengage Learning
Rotor Construction
• Rotor: magnetic field that rotates within the
stator’s wire windings
– Very little clearance to maintain strong field
– Field coil has electrical wire wound around a
shaft
– Poles fit into each other
• Make several pairs of north and south poles
• Increases magnetic flux
– Average rotor can spin at about 13,500 rpm
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Stator Windings
• Three sets of
windings wrapped
around slots in
laminated round
iron frame (i.e.,
core)
– Each winding has
two leads: one for
current to enter
and one to exit
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Rectifier Construction
• Diode rectifier converts AC to DC
–
–
–
–
When AC current reverses, the diode blocks
A pair of diodes is used for each stator winding
Three positive diodes are mounted in a heat sink
Three negative diodes mounted in the alternator
frame
• Three phases of AC are rectified
– Result is almost uniform DC voltage
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
AC Generator Bearings
• Rotor is supported in alternator housing using
ball or roller bearings
– Bearings are usually sealed and packed with
grease
– Front bearing fits into indent in the case
– Rear bearing is pressed-fit into the case
– Rotor shaft slides into rear bearing
• AC generator fan
– Cooling fan draws air into AC generator
© 2012 Delmar, Cengage Learning
Voltage Regulator
• Controls current passing through windings of
electromagnetic field in the rotor
– Determines amount of current produced in stator
– Increases current output when charging system
voltage is low
• Electronic voltage regulators
– No moving parts or contacts: very reliable
– Zener diode conducts electricity when a certain
voltage is reached
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Voltage Regulator (cont'd.)
• Computer voltage regulation/pulse
– Voltage regulation on late-model vehicles is done
by the on-board computer, or powertrain control
module
– Electronic voltage regulation: can cycle 10-7,000
times per second
– Pulse width modulation: turning alternator on and
off rapidly
© 2012 Delmar, Cengage Learning
Charging System Indicators
• Charge indicators
– Warning light
– Voltmeter
– Ammeter
• AC generator warning light
– Wired into charging circuit
• Voltmeter indicator
– Shows system voltage when engine is running
• Ammeter indicator
– Gives current amount flowing to or from battery
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
High-Voltage Charging Systems
• Important dates and concepts
– 1970: automobile required about 500 watts
– 2008: vehicle requires about 4,000 watts
– 2020: BAS systems will be included on all
internal combustion engine vehicles
• BAS systems use 42-volt electrical systems with a
36-volt battery pack
• BAS motor/generator: larger than conventional AC
generator
© 2012 Delmar, Cengage Learning
High-Voltage Charging Systems
(cont'd.)
• Hybrid vehicles
– More electrically
powered components
– Use a generator with
inverter/converter
• Converts battery
pack voltage to low
voltage to power the
computer and
accessories
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning