Download - Alternator DC

7/31/2019 Alternator DC

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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
http://www.autoshop101.com/http://www.autoshop101.com/


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The charging system has threemajor components. The

Battery, Alternator, and theRegulator.

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

The output of an alternator is

direct current, however ACvoltage is actually created and

then converted to DC as voltageleaves the alternator on its way

to the battery and the electricalloads.

TheCharging System


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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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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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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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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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Most regulators are on the insidethe alternator. Older models have

externally mounted regulators.

Unlike other manufacturers, this

model can be easily serviced fromthe rear on the unit.

The rear cover can be removed toexpose internal parts.

However, todays practice is tocorrectly diagnose the problemand replace the alternator as a

unit, should one of its internalcomponents fail.

Alternator Design


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Alternator drive pulleys eitherbolt on or are pressed on the

rotor shaft.

Both V and Multi-grove typesare used.

Note this alternator does not

have an external fan as part ofthe pulley assembly.

While many manufacturers do

use a external fan for cooling.This alternator has two internal

fans to draw air in for cooling.

Drive Pulley


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Removal of the rear coverreveals:Brushes

Diode Rectifier Bridge

Regulator

Inside the Alternator

The Rectifier Bridge converts

AC 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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Two slip rings are located on oneend of the rotor assembly. Each

end 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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The regulator is the brain of thecharging system.

It monitors both battery and

stator voltages and dependingon the measured voltages, the

regulator will adjust the amountof rotor field current to control

alternator output.

Regulators can be mountedboth internal or external.

Current technology uses aninternal regulator.

ElectronicIC Regulator


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The Diode Rectifier Bridge isresponsible for for the

conversion 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 on

the positive side and the other

half are on the negative side.

Further details about the

rectifier bridge will be explainedlater.

Diode Rectifier


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Inside the Alternator

Stator WindingRotor WindingAssembly

Separating the case reveals:

The stator winding developsvoltage and current begins

to flow from the inducedmagnetic field of the rotor.

The rotor winding assembly

rotates inside the statorwinding. The rotor generatesa magnetic field.


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Slip Rings

Bearing

Internal Cooling Fan

Rotor Assembly

Finger Poles Rotor Field Winding

Rotor Shaft

InternalCooling Fan


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A basic rotor consists of a ironcore, coil winding, two slip rings,

and two claw-shaped finger pole

pieces.

Some models include support

bearings and one or two internalcooling fans.

The rotor is driven or rotated

inside the alternator by anengine (alternator) drive belt.

Rotor Assembly


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The rotor contains the fieldwinding wound over an iron

core which is part of the shaft.

Surrounding the field coil are

two claw-type finger poles.

Each end of the rotor field

winding is attached to a slipring. Stationary brushes

connect the alternator to the

rotor.

The rotor assembly is supported

by bearings. One on the shaftthe other in the drive frame.

Rotor Assembly


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The rotor field winding createsthe magnetic field that induces

voltage into the stator.

The magnetic field is saturatesthe iron finger poles. One finger

pole become a north pole andthe other a south pole.

The rotor spins creating an

alternating magnetic field,North, South, North, South, etc.

North Field

South Field

North Field

AlternatingMagnetic Field


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Stator Winding

Laminated IronFrame

StatorLead Ends

Three PhaseWindings

NeutralJunction


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As the rotor assembly rotateswithin the stator winding.

The alternating magnetic field

from the spinning rotor inducesan alternating voltage into the

stator winding.

The strength of the magneticfield and the speed of the rotor

affect the amount of voltageinduced into the stator.

Rotor / StatorRelationship


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The stator is made with three setsof windings.

Each winding is placed is a

different position compared with

the others.

A laminated iron frame

concentrates the magnetic field.

Stator lead ends that output tothe diode rectifier bridge.

Laminated IronFrame

Stator Lead Ends

Stator Windings

Three Windings

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


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The stator winding has threesets of windings. Each is formed

into 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 together

make up the total AC output of

the stator. This is called threephase current.

Three phase current provides amore even current output.

3 Phase Windings


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Stator Design

Two designs of stator windingare used. Delta and Wye.

Wye style has four stator leads. Oneof the leads is called the Neutral

Junction. The Neutral Junction iscommon to all the other leads.

Delta wound stators can be identifiedby having only three stator leads, and

each lead will have the same numberof wires attached.


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Wye Design Wye wound stators have threewindings with a common neutral

junction. 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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Delta Design Delta wound stators can beidentified because they have only

three stator lead ends.

Delta stators allow for highercurrent flow being delivered at low

RPM.

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


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Diode Rectifier Bridge Assembly

Ground Points

B Terminal

P TerminalStator Taps

Attaches toStator Windings

Negative Diodes

Positive Diodes


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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 to

rectify the AC stator voltage toDC voltage.

Diodes used in this configurationwill redirect both the positive andnegative polarity signals of the

AC voltage to produce DCvoltage. This process is called

Full - Wave Rectification.

RectifierOperation

The Diode Rectifier Bridge isresponsible for for the conversion or

rectification the AC voltage into DCvoltage.


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Diodes are used as one-wayelectrical check valves. Passing

current in only one direction,

never in reverse.

Diodes are mounted in a heat

sink to dissipate the heatgenerated by the diodes.

Diodes redirect the AC voltage

into DC voltage so the batteryreceives the correct polarity.

Diodes

Diodes


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Rectifier OperationIn red you can see B+ current

pass through to the rectifier as

it goes to the battery. In green

you can see the return path.

Now, in red B+ current passes

through to the rectifier

however, this time current has

the opposite polarity. In green

you can see the new return

path.

Even though it enters therectifier at a different location,

current goes to the battery inthe same direction.


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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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The regulator will attempt tomaintain a pre-determined

charging system voltage level.

When charging system voltage

falls 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 field

current , thus weakening themagnetic field, and results in a

decrease of alternator output.

Voltage Regulation


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Any one of two regulatordesigns can be used.

The Grounded Field type.The regulator controls theamount of B+ going to the

field winding in the rotor.

Regulator Types

The Grounded Regulator

type. The regulatorcontrols the amountbattery ground (negative)

going to the field windingin the rotor.

B+

ALTERNATORREGULATOR

B+

Field

Coil

ALTERNATORREGULATOR

Field

Coil

B+


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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 use

by the vehicle.