© 2012 delmar, cengage learning charging system fundamentals chapter 30

© 2012 Delmar, Cengage Learning

Charging System Fundamentals

Chapter 30


Objectives• Explain electrical generation principles• Describe AC generator parts• Explain the operation of a voltage regulator


Introduction• Charging system

– Important part of electrical system

– Allows battery to maintain charge and operate accessories


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


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


AC Generator/Alternator• Alternator is an AC

generator– Electromagnet

passes across wire to induce voltage

• Stator: stationary conductor

• Rotor: rotating electromagnetic field


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


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


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


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


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


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


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


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


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 charging system fundamentals chapter 30

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