UnderstandingtheAlternator

Kevin Sullivan, all rights reserved. www.autoshop101.com

THIS AUTOMOTIVE SERIES

ON ALTERNATORS HAS
BEEN DEVELOPED BY

KEVIN R. SULLIVAN
PROFESSOR OF
AUTOMOTIVE TECHNOLOGY
AT SKYLINE COLLEGE
SAN BRUNO, CALIFORNIA
ALL RIGHTS RESERVED

http://www.autoshop101.com

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
The
Charging System

The charging system has three

major components. The Battery,
Alternator, and the Regulator.

This alternator works together

with the battery to supply power
when the vehicle is running.

The output of an alternator is

direct current, however AC
voltage is actually created and
then converted to DC as voltage
leaves the alternator on its way
to the battery and the electrical
loads.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Charging System Circuit

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.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Alternator Terminal Identification

S Terminal
Senses Battery
Voltage

L Terminal
Grounds
Warning Lamp

F Terminal
Regulator Bypass
Full Field Testing

B Terminal
Alternator Output
Terminal to Battery

IG Terminal
Ignition Switch Signal
Turns Regulator ON

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Kevin Sullivan, all rights reserved. www.autoshop101.com

Alternator Assembly
Drive Frame Cover

Identification
Label

End Frame Cover

Drive Pulley

Regulator, Diode,
& Brush Cover

Circulation Vent

Alternator B+
Output Terminal

Mounting Ear

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UnderstandingtheAlternator
Alternator
Overview

The alternator contains:

A rotating field winding called

the rotor.

A stationary induction winding

called the stator.

A diode assembly called the

rectifier bridge.

A control device called the

voltage regulator.

Two internal fans to promote air

circulation.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Alternator Design

Most regulators are on the inside

the alternator. Older models have
externally mounted regulators.

Unlike other manufacturers, this

model can be easily serviced from
the rear on the unit.

The rear cover can be removed to

expose internal parts.

However, todays practice is to

correctly diagnose the problem and
replace the alternator as a unit,
should one of its internal
components fail.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Drive Pulley

Alternator drive pulleys either

bolt on or are pressed on the
rotor shaft.

Both V and Multi-grove types

are used.

Note this alternator does not

have an external fan as part of
the pulley assembly.

While many manufacturers do

use a external fan for cooling.
This alternator has two internal
fans to draw air in for cooling.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Inside the Alternator

Regulator

Brushes

Removal of the rear cover

reveals:
The Regulator controls the
alternator output.
The Brushes conduct current
to the rotor field winding.
The Rectifier Bridge converts
AC voltage to DC voltage.

Diode Rectifier Bridge

Slip Rings (part of the Rotor Assembly)

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Brushes

Two slip rings are located on one end

of the rotor assembly. Each end of
the rotor field winding is attached to a
slip ring. Thereby, allowing current to
flow through the field winding.

Two stationary carbon brushes

ride on two rotating slip rings.
Bushes are either soldered or
bolted

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
Electronic
IC Regulator

The regulator is the brain of the

charging system.

It monitors both battery and stator

voltages. Depending on the
measured voltages, the regulator
will adjust the amount of rotor field
current to control alternator output.

Regulators can be mounted both

internal or external. Current
technology uses an internal
regulator.

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
Diode Rectifier

The Diode Rectifier Bridge is

responsible for for the
conversion or rectification of AC
voltage to DC voltage.

Six or eight diodes are used to

rectify the AC stator voltage to
DC 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 explained later.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Inside the Alternator

Separating the case reveals:
The rotor winding assembly
rotates inside the stator
winding. The rotor generates
a magnetic field.
The stator winding develops
voltage and current begins to
flow from the induced
magnetic field of the rotor.
Rotor Winding
Assembly

Stator Winding

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Rotor Assembly
Internal Cooling Fan

Finger Poles

Rotor Field Winding

Bearing

Internal
Cooling Fan

Slip Rings

Rotor Shaft

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Rotor Assembly

A basic rotor consists of a iron

core, coil winding, two slip rings,
and two claw-shaped finger pole
pieces.

Some models include support

bearings and one or two internal
cooling fans.

The rotor is driven or rotated

inside the alternator by an
engine (alternator) drive belt.

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
Rotor Assembly

The rotor contains the field

winding 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 slip ring.
Stationary brushes connect the
alternator to the rotor.

The rotor assembly is supported

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

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
Alternating
Magnetic Field

The rotor field winding creates

the magnetic field that induces
voltage into the stator.

The magnetic field is saturates

the iron finger poles. One finger
pole become a north pole and
the other a south pole.

The rotor spins creating an

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

North Field

South Field

North Field

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Stator Winding
Stator
Lead Ends

Neutral
Junction

Laminated Iron
Frame
Three Phase
Windings

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UnderstandingtheAlternator
Rotor / Stator
Relationship

As the rotor assembly rotates

within the stator winding.

The alternating magnetic field

from the spinning rotor induces
an alternating voltage into the
stator winding.

Both the strength of the

magnetic field and the speed of
the rotor affect the amount of
voltage induced into the stator.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Stator Windings
Stator Lead Ends

Laminated Iron
Frame

The stator is made with three sets

of 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 to the

diode rectifier bridge.

Three Windings

Neutral Junction in the Wye design can

be identified by the 6 strands of wire

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

3 Phase Windings

The stator winding has three sets

of windings. Each is formed into
a number of evenly spaced coils
around the stator core.

The result is three overlapping

single phase AC sine wave
current signatures, A, B, C.

Adding these waves together

make up the total AC output of
the stator. This is called three
phase output current.

Three phase current provides a

more constant current output.

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UnderstandingtheAlternator
Stator Design

Two designs of stator winding

are used. Delta and Wye.

Delta wound stators can be identified

by having only three stator leads, and
each lead will have the same number
of wires attached.

Wye style has four stator leads. One

of the leads is called the Neutral
Junction. The Neutral Junction is
common to all the other leads.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Wye Design

Wye wound stators have three

windings with a common neutral
junction. They can be identified
because they have 4 stator lead
ends.
Wye wound stators are used in
alternators that require high voltage
output a low alternator speed.
Two windings are in series at any
one time during charge output.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Delta Design

Delta wound stators can be

identified because they have only
three stator lead ends.
Delta stators allow for higher
current flow being delivered at low
RPM.
The windings are in parallel rather
than series as like the Wye design.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Diode Rectifier Bridge Assembly

Negative Diodes

Ground Points
B Terminal

P Terminal
Stator Taps
Attaches to
Stator Windings

Positive Diodes

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
Rectifier
Operation

The Diode Rectifier Bridge is

responsible for for the conversion or
rectification the AC voltage into DC
voltage.

Two diodes are connected to each

stator lead. One positive the other
negative.

Because a single diode will only

block half the the AC voltage.

Six or eight diodes are used to

rectify the AC stator voltage to DC
voltage.

Diodes used in this configuration will

redirect both the positive and
negative polarity signals of the AC
voltage to produce DC voltage. This
process is called Full - Wave
Rectification.

Kevin Sullivan, all rights reserved. www.autoshop101.com

UnderstandingtheAlternator
Diodes

Diodes are used as one-way

electrical check valves. Passing
current in only one direction,
never in reverse.

Diodes are mounted in a heat

sink to dissipate the heat
generated by the diodes.

Diodes redirect the AC voltage

into DC voltage so the battery
receives the correct polarity.

Diodes

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Rectifier Operation

In 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 the

rectifier at a different location,
current goes to the battery in
the same direction.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Electronic Regulator
Heat Sink

S Terminal

L Terminal

Senses Battery Voltage

Warning Lamp

IG Terminal
Ignition Switch Signal
Turns Regulator ON

Regulator
Ground

B Terminal
Connects to Alternator
Output Terminal

P Terminal

F Terminal Test Pad

F Terminal

Senses Neutral Junction

voltage of Stator

Full Field Test Point

Connects Regulator
to Rotor Winding

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Voltage Regulation

The regulator will attempt to

maintain a pre-determined charging
system voltage level.

When charging system voltage falls

below this point, the regulator will
increase the field current, thus
strengthening the magnetic field,
which results in an increase of
alternator output.

When charging system voltage

raises above this point, the
regulator will decrease field current ,
thus weakening the magnetic field,
and results in a decrease of
alternator output.

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Regulator Types
REGULATOR
ALTERNATOR
B+
Field

Any one of two regulator

designs can be used.

The Grounded Field type.

The regulator controls the
amount of B+ going to the
field winding in the rotor.

The Grounded Regulator

type. The regulator
controls the amount
battery ground (negative)
going to the field winding
in the rotor.

Coil

REGULATOR
ALTERNATOR
B+
Field

Coil

UnderstandingtheAlternator
Kevin Sullivan, all rights reserved. www.autoshop101.com

Working Alternator
Regulator

The regulator monitors battery

voltage.
The regulator controls current
flow to the rotor assembly.
The rotor produces a magnetic
field.
Voltage is induced into the stator.
The rectifier bridge converts AC
stator voltage to DC output for use
by the vehicle.
Diode Rectifier Bridge
Contains the Rotor & Stator

Slip Rings (part of the Rotor Assembly)