© 2012 Delmar, Cengage Learning Charging System Fundamentals Chapter 30.
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Transcript of © 2012 Delmar, Cengage Learning 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
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
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
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
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
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
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
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