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Understanding the Alternator

THIS AUTOMOTIVE SERIESON ALTERNATORS HASBEEN DEVELOPED BY

KEVIN R. SULLIVAN

PROFESSOR OFAUTOMOTIVE TECHNOLOGY

AT SKYLINE COLLEGESAN BRUNO, CALIFORNIA

ALL RIGHTS RESERVED

http://www.autoshop101.com

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Understanding the Alternator

• The charging system has threemajor components. TheBattery, Alternator, and theRegulator.

• This alternator works togetherwith the battery to supply powerwhen the vehicle is running.

• The output of an alternator isdirect current, however ACvoltage is actually created andthen converted to DC as voltageleaves the alternator on its wayto the battery and the electricalloads.

TheCharging System

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Understanding the Alternator

• Four wires connect the alternator to the rest of the charging system.

• B is the alternator output wire that supplies current to the battery.

• IG is the ignition input that turns on the alternator/regulator assembly.

• S is used by the regulator to monitor charging voltage at the battery.

• L is the wire the regulator uses to ground the charge warning lamp.

Charging System Circuit

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Understanding the Alternator

Alternator Terminal Identification

“B” TerminalAlternator Output

Terminal to Battery

“L” TerminalGrounds

Warning Lamp

“S” TerminalSenses Battery

Voltage

“F” TerminalRegulator BypassFull Field Testing

“IG” TerminalIgnition Switch SignalTurns Regulator ON

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Understanding the Alternator

Alternator B+Output Terminal

Regulator, Diode,& Brush Cover

End Frame CoverDrive Frame Cover

Drive Pulley

Mounting Ear

Circulation Vent

IdentificationLabel

Alternator Assembly

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Understanding the Alternator

• The alternator contains:

• A rotating field winding calledthe rotor.

• A stationary induction windingcalled the stator.

• A diode assembly called therectifier bridge.

• A control device called thevoltage regulator.

• Two internal fans to promote aircirculation.

AlternatorOverview

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Understanding the Alternator

• Most regulators are on the insidethe alternator. Older models haveexternally mounted regulators.

• Unlike other manufacturers, thismodel can be easily serviced fromthe rear on the unit.

• The rear cover can be removed toexpose internal parts.

• However, today’s practice is tocorrectly diagnose the problemand replace the alternator as aunit, should one of it’s internalcomponents fail.

Alternator Design

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Understanding the Alternator

• Alternator drive pulleys eitherbolt on or are pressed on therotor shaft.

• Both ‘V’ and Multi-grove typesare used.

• Note this alternator does nothave an external fan as part ofthe pulley assembly.

• While many manufacturers douse a external fan for cooling.This alternator has two internalfans to draw air in for cooling.

Drive Pulley

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Understanding the Alternator

• Removal of the rear coverreveals:Brushes

Diode Rectifier Bridge

Regulator

Inside the Alternator

The Rectifier Bridge convertsAC voltage to DC voltage.

The Brushes conduct currentto the rotor field winding.

The Regulator controls thealternator output.

Slip Rings (part of the Rotor Assembly)

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Understanding the Alternator

• Two slip rings are located on oneend of the rotor assembly. Eachend of the rotor field winding isattached to a slip ring. Thereby,allowing current to flow throughthe field winding.

• Two stationary carbon brushesride on two rotating slip rings.Bushes are either soldered orbolted

Brushes

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Understanding the Alternator

• The regulator is the brain of thecharging system.

• It monitors both battery andstator voltages and dependingon the measured voltages, theregulator will adjust the amountof rotor field current to controlalternator output.

• Regulators can be mountedboth internal or external.Current technology uses aninternal regulator.

ElectronicIC Regulator

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Understanding the Alternator

• The Diode Rectifier Bridge isresponsible for for theconversion or rectification of ACvoltage to DC voltage.

• Six or eight diodes are used torectify the AC stator voltage toDC voltage.

• Half of these diodes are use onthe positive side and the otherhalf are on the negative side.

• Further details about therectifier bridge will be explainedlater.

Diode Rectifier

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Understanding the Alternator

Inside the Alternator

Stator WindingRotor WindingAssembly

• Separating the case reveals:

The stator winding developsvoltage and current beginsto flow from the inducedmagnetic field of the rotor.

The rotor winding assemblyrotates inside the statorwinding. The rotor generatesa magnetic field.

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Understanding the Alternator

Slip Rings

Bearing

Internal Cooling Fan

Rotor Assembly

Finger Poles Rotor Field Winding

Rotor Shaft

InternalCooling Fan

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Understanding the Alternator

• A basic rotor consists of a ironcore, coil winding, two slip rings,and two claw-shaped finger polepieces.

• Some models include supportbearings and one or two internalcooling fans.

• The rotor is driven or rotatedinside the alternator by anengine (alternator) drive belt.

Rotor Assembly

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Understanding the Alternator

• The rotor contains the fieldwinding wound over an ironcore which is part of the shaft.

• Surrounding the field coil aretwo claw-type finger poles.

• Each end of the rotor fieldwinding is attached to a slipring. Stationary brushesconnect the alternator to therotor.

• The rotor assembly is supportedby bearings. One on the shaftthe other in the drive frame.

Rotor Assembly

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Understanding the Alternator

• The rotor field winding createsthe magnetic field that inducesvoltage into the stator.

• The magnetic field is saturatesthe iron finger poles. One fingerpole become a north pole andthe other a south pole.

• The rotor spins creating analternating magnetic field,North, South, North, South, etc.

North Field

South Field

North Field

AlternatingMagnetic Field

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Understanding the Alternator

Stator Winding

Laminated IronFrame

StatorLead Ends

Three PhaseWindings

NeutralJunction

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Understanding the Alternator

• As the rotor assembly rotateswithin the stator winding.

• The alternating magnetic fieldfrom the spinning rotor inducesan alternating voltage into thestator winding.

• The strength of the magneticfield and the speed of the rotoraffect the amount of voltageinduced into the stator.

Rotor / StatorRelationship

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Understanding the Alternator

• The stator is made with three setsof windings.

• Each winding is placed is adifferent position compared withthe others.

• A laminated iron frameconcentrates the magnetic field.

• Stator lead ends that output tothe diode rectifier bridge.

Laminated IronFrame

Stator Lead Ends

Stator WindingsThree Windings

Neutral Junction in the Wye design canbe identified by the 6 strands of wire

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Understanding the Alternator

• The stator winding has threesets of windings. Each is formedinto a number of evenly spacedcoils around the stator core.

• The result is three overlappingsingle phase AC sine wavecurrent signatures, A, B, C.

• Adding these waves togethermake up the total AC output ofthe stator. This is called threephase current.

• Three phase current provides amore even current output.

3 Phase Windings

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Understanding the Alternator

Stator Design

Two designs of stator windingare used. Delta and Wye.

Wye style has four stator leads. Oneof the leads is called the NeutralJunction. The Neutral Junction iscommon to all the other leads.

Delta wound stators can be identifiedby having only three stator leads, andeach lead will have the same numberof wires attached.

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Understanding the Alternator

Wye Design Wye wound stators have threewindings with a common neutraljunction. They can be identifiedbecause they have 4 stator leadends.

Wye wound stators are used inalternators that require high voltageoutput a low alternator speed.

Two windings are in series at anyone time during charge output.

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Understanding the Alternator

Delta Design Delta wound stators can beidentified because they have onlythree stator lead ends.

Delta stators allow for highercurrent flow being delivered at lowRPM.

The windings are in parallel ratherthan series as like the Wye design.

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Understanding the Alternator

Diode Rectifier Bridge Assembly

Ground Points

“B” Terminal

“P” TerminalStator Taps

Attaches toStator Windings

Negative Diodes

Positive Diodes

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Understanding the Alternator

• Two diodes are connected toeach stator lead. One positive theother negative.

• Because a single diode will onlyblock half the the AC voltage.

• Six or eight diodes are used torectify the AC stator voltage toDC voltage.

• Diodes used in this configurationwill redirect both the positive andnegative polarity signals of theAC voltage to produce DCvoltage. This process is called‘Full - Wave Rectification’.

RectifierOperation

The Diode Rectifier Bridge isresponsible for for the conversion orrectification the AC voltage into DCvoltage.

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Understanding the Alternator

• Diodes are used as one-wayelectrical check valves. Passingcurrent in only one direction,never in reverse.

• Diodes are mounted in a heatsink to dissipate the heatgenerated by the diodes.

• Diodes redirect the AC voltageinto DC voltage so the batteryreceives the correct polarity.

Diodes

Diodes

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Understanding the Alternator

Rectifier OperationIn red you can see B+ currentpass through to the rectifier asit goes to the battery. In greenyou can see the return path.

Now, in red B+ current passesthrough to the rectifierhowever, this time current hasthe opposite polarity. In greenyou can see the new returnpath.

Even though it enters therectifier at a different location,current goes to the battery inthe same direction.

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Understanding the Alternator

“B” TerminalConnects to Alternator

Output Terminal

“L” TerminalWarning Lamp

“S” TerminalSenses Battery Voltage

“F” TerminalConnects Regulator

to Rotor Winding

“IG” TerminalIgnition Switch SignalTurns Regulator ON

Heat Sink

“P” TerminalSenses Neutral Junction

voltage of Stator

RegulatorGround

Electronic Regulator

“F” Terminal Test PadFull Field Test Point

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Understanding the Alternator

• The regulator will attempt tomaintain a pre-determinedcharging system voltage level.

• When charging system voltagefalls below this point, the regulatorwill increase the field current, thusstrengthening the magnetic field,which results in an increase ofalternator output.

• When charging system voltageraises above this point, theregulator will decrease fieldcurrent , thus weakening themagnetic field, and results in adecrease of alternator output.

Voltage Regulation

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Understanding the Alternator

• Any one of two regulatordesigns can be used.

• The Grounded Field type.The regulator controls theamount of B+ going to thefield winding in the rotor.

Regulator Types

• The Grounded Regulatortype. The regulatorcontrols the amountbattery ground (negative)going to the field windingin the rotor.

B+

ALTERNATORREGULATOR

B+

FieldCoil

ALTERNATORREGULATOR

FieldCoil

B+

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Understanding the Alternator

Slip Rings (part of the Rotor Assembly)

Diode Rectifier Bridge

Regulator

Working Alternator

Contains the Rotor & Stator

The regulator monitors batteryvoltage.

The regulator controls currentflow to the rotor assembly.

The rotor produces a magneticfield.

Voltage is induced into the stator.

The rectifier bridge converts ACstator voltage to DC output for useby the vehicle.