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
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Understanding the Alternator
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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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 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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Understanding the Alternator
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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Understanding the Alternator
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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Understanding the Alternator
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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Understanding the Alternator
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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Understanding the Alternator
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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Understanding the Alternator
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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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 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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Understanding the Alternator
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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Understanding the Alternator
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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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 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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Understanding the Alternator
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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Understanding the Alternator
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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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 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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Understanding the Alternator
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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Understanding the Alternator
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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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 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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Understanding the Alternator
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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Understanding the Alternator
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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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-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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Understanding the Alternator
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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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 use
by the vehicle.
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