learning objectives

LEARNINGOBJECTIVESUpon completion and review of this chapter, youshould be able to:

• Identify charging system development andprinciples.

• Explain the operation of a DC generator.• Identify AC charging system components

and explain charging voltage.• Explain diode rectification.• Identify AC generator components and

explain their function.• Explain current production in an AC gener-

ator (alternator) operation.• Identify different OEM AC generators and

explain those differences.• Explain how voltage is regulated in an AC

generator.• Identify the different types of voltage regu-

lators and explain how they operate.

KEY TERMSAC GeneratorsDelta-Type StatorDiodeField CircuitFull-Wave RectificationHalf-Wave RectificationOutput CircuitRotorSine Wave VoltageSingle-Phase CurrentSingle-Phase VoltageSliprings and BrushesStatorThree-phase CurrentVoltage RegulatorY-Type Stator

INTRODUCTIONThe charging system converts the engine’smechanical energy into electrical energy. Thiselectrical energy is used to maintain the battery’sstate of charge and to operate the loads of the auto-motive electrical system. In this chapter we willuse the conventional theory of current: Electronsmove from positive to negative (� to �).

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8ChargingSystemOperation

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148 Chapter Eight

FIELD

LAMINATEDCORE

OUTPUTWAVE

COMMUTATOR

CARBON BRUSH

LINES OFFORCE

WIRE LOOP

Figure 8-1. DC generator.

During cranking, all electrical energy for thevehicle is supplied by the battery. After the engineis running, the charging system must produceenough electrical energy to recharge the batteryand to supply the demands of other loads in theelectrical system. If the starting system is in poorcondition and draws too much current, or if thecharging system cannot recharge the battery andsupply the additional loads, more energy must bedrawn from the battery for short periods of time.

CHARGING SYSTEMDEVELOPMENTFor many years, automotive charging systems usedonly direct current (DC) generators to provideelectrical energy. Internally, generators produce analternating current voltage, which is mechanicallyrectified by the commutator into direct currentvoltage. Systems using DC generators are calledDC charging systems. Vehicles with DC generatorsare very rare today.

AC generators or alternators also produce alter-nating current (AC), but there was no simple wayto rectify the current until semiconductor technol-ogy finally provided the answer in the form ofdiodes, or one-way electrical valves. Since themid-1960s, virtually all new automobiles havediode-rectified AC generators (alternators) in theircharging systems.

AC generators (alternators) replaced DC gener-ators back in the late fifties, except for Volkswagen,which used DC generators until 1975. In the auto-motive charging system, they have the followingadvantages:

• Weigh less per ampere of output• Can be operated at much higher speed• Pass less current through the brushes with

only a few amperes of field current, reduc-ing brush wear

• Govern their own maximum current output,requiring no external current regulation

• Can produce current when rotated in eitherdirection, although their cooling fans usu-ally are designed for one-way operation.

DC GENERATORThe principles of electromagnetic induction areemployed in generators for producing DC cur-rent. The basic components of a DC generator are

shown in Figure 8-1. A framework composed oflaminated iron sheets or other ferromagneticmetal has a coil wound on it to form an electro-magnet. When current flows through this coil,magnetic fields are created between the polepieces, as shown. Permanent magnets could alsobe employed instead of the electromagnet.

To simplify the initial explanation, a single wireloop is shown between the north and south polepieces. When this wire loop is turned within themagnetic fields it cuts the lines of force and a volt-age is induced. If there is a complete circuit from thewire loop, current will flow. The wire loop is con-nected to a split ring known as a commutator, andcarbon brushes pick off the electric energy as thecommutator rotates. Connecting wires from the car-bon brushes transfer the energy to the load circuit.

When the wire loop makes a half-turn, the energygenerated rises to a maximum level and drops tozero, as shown in Figure 8-1. If the wire loop com-pleted a full rotation, the induced voltage wouldreverse itself and the current would flow in theopposite direction (AC current) after the initial half-turn. To provide for an output having a single polar-ity (DC current), a split-ring commutator is used.Thus, for the second half-turn, the carbon brushesengage commutator segments opposite to thoseover which they slid for the first half-turn, keepingthe current in the same direction. The output wave-form is not a steady-level DC, but rises and falls toform a pattern referred to as pulsating DC. Thus, fora complete 360-degree turn of the wire loop, twowaveforms are produced, as shown in Figure 8-1.

CHARGING VOLTAGEAlthough the automotive electrical system is calleda 12-volt system, the AC generator (alternator)must produce more than 12 volts. A fully charged

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Charging System Operation 149

Figure 8-3. An AC generator (alternator) is based onthe rotation of a magnet inside a fixed-loop conductor.(DaimlerChrysler Corporation)

battery produces about 2.1 volts per cell; this meansthe open-circuit voltage of a fully charged 12-voltbattery, which has six cells, is approximately12.6 volts. If the AC generator cannot produce morethan 12.6 volts, it cannot charge the battery until thesystem voltage drops under 12.6 volts. This wouldleave nothing extra to serve the other electricaldemands put on the system by lights, air condition-ing, and power accessories.

Alternating-current charging systems are gener-ally regulated to produce a maximum output of14.5 volts. Output of more than 16 volts will over-heat the battery electrolyte and shorten its life. Highvoltage also damages components that rely heavilyon solid-state electronics, such as fuel injection andengine control systems. On the other hand, lowvoltage output causes the battery to become sul-fated. The charging system must be maintainedwithin the voltage limits specified by the manufac-turer if the vehicle is to perform properly.

AC Charging SystemComponentsThe automotive charging system. (Figure 8-2)contains the following:

• A battery, which provides current to initiatethe magnetic field required to operate the ACgenerator (alternator) and, in turn, is chargedand maintained by the AC generator.

• An AC generator (alternator), which is belt-driven by the engine and converts mechanicalmotion into charging voltage and current.

The simple AC generator (alternator) shown inFigure 8-3 consists of a magnet rotating inside afixed-loop stator, or conductor. The alternating

current produced in the conductor is rectified bydiodes for use by the electrical system.

• A voltage regulator, which limits the fieldcurrent and thus the AC generator (alterna-tor) output voltage according to the electricalsystem demand. A regulator can be either anelectromechanical or a solid-state device.Some late-model, solid-state regulators arepart of the vehicle’s onboard computer.

• An ammeter, a voltmeter, or indicator warn-ing lamp mounted on the instrument panelto give a visual indication of charging sys-tem operation.

Charging System CircuitsThe charging system consists of the followingmajor circuits (Figure 8-4):

• The field circuit, which delivers current tothe AC generator (alternator) field

• The output circuit, which sends voltage andcurrent to the battery and other electricalcomponents

Single-Phase CurrentAC Generators (alternators) induce voltage byrotating a magnetic field inside a fixed conductor.The greatest current output is produced when therotor is parallel to the stator with its magnetic fieldat right angles to the stator, as in Figure 8-3. Whenthe rotor makes one-quarter of a revolution and isat right angles to the stator with its magnetic fieldparallel to the stator, as in Figure 8-5, there is no

Figure 8-2. Major components of an automotive charg-ing system. (DaimlerChrysler Corporation)

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Figure 8-4. The output circuit and the field circuit makeup the automotive charging system. (DaimlerChryslerCorporation)

Figure 8-6. These are the voltage levels inducedacross the upper half of the conductor during one rotorrevolution. (DaimlerChrysler Corporation)

current output. Figure 8-6 shows the voltage lev-els induced across the upper half of the loopedconductor during one revolution of the rotor.

The constant change of voltage, first to a posi-tive peak and then to a negative peak, produces asine wave voltage. This name comes from thetrigonometric sine function. The wave shape iscontrolled by the angle between the magnet andthe conductor. The sine wave voltage inducedacross one conductor by one rotor revolution iscalled a single-phase voltage. Positions 1 through5 of Figure 8-6 show complete sine wave single-phase voltage.

This single-phase voltage causes alternating cur-rent to flow in a complete circuit because the volt-age switches from positive to negative as the rotor

turns. The alternating current caused by a single-phase voltage is called single-phase current.

DIODERECTIFICATIONIf the single-phase voltage shown in Figure 8-6made current travel through a simple circuit, thecurrent would flow first in one direction and then inthe opposite direction. As long as the rotor turned,the current would reverse its flow with every halfrevolution. The battery cannot be recharged withalternating current. Alternating current must be rec-tified to direct current to recharge the battery. Thisis done with diodes.

A diode acts as a one-way electrical valve. If adiode is inserted into a simple circuit, as shown inFigure 8-7, one-half of the AC voltage is blocked.That is, the diode allows current to flow from X toY, as shown in position A. In position B, the cur-rent cannot flow from Y to X because it is blockedby the diode. The graph in Figure 8-7 shows thetotal current.

The first half of the current, from X to Y, wasallowed to pass through the diode. It is shown onthe graph as curve XY. The second half of the cur-rent, from Y to X, was not allowed to pass throughthe diode. It does not appear on the graph becauseit never traveled through the circuit. When the

Figure 8-5. No current flows when the rotor’s magneticfield is parallel to the stator. (DaimlerChrysler Corporation)

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Figure 8-7. A single diode in the circuit results in half-wave rectification. (Delphi Automotive Systems)

voltage reverses at the start of the next rotor rev-olution, the current is again allowed through thediode from X to Y.

An AC generator with only one conductor andone diode would show this current output pattern.However, this output would not be very usefulbecause half of the time there is no current avail-able. This is called half-wave rectification, sinceonly half of the AC voltage produced by the ACgenerator is allowed to flow as DC voltage.

Adding more diodes to the circuit, as shown inFigure 8-8, allows more of the AC voltage to berectified to DC. In position A, current moves fromX to Y. It travels from X, through diode 2, throughthe load, through diode 3, and back to Y. In posi-tion B, current moves from Y to X. It travels fromY, through diode 4, through the load, throughdiode I, and back to X.

Notice that in both cases current traveledthrough the load in the same direction. This isbecause the AC has been rectified to DC. Thegraph in Figure 8-8 shows the current output of anAC generator with one conductor and four diodes.

Figure 8-8. More diodes are needed in the circuit for full-waverectification. (Delphi Automotive Systems)

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There is more current available because all of thevoltage has been rectified. This is called full-waverectification. However, there are still momentswhen current is at zero. Most automotive ACgenerators use three conductors and six diodes toproduce overlapping current waves so that currentoutput is never at zero.

� Heat Sinks

The term heat sink is commonly used to describethe block of aluminum or other material in whichthe AC generator diodes are mounted. The job ofthe heat sink is to absorb and carry away the heatin the diodes caused by electrical current throughthem. This action keeps the diodes cool and pre-vents damage. An internal combustion engine isalso a heat sink.The engine is designed so that thecombustion and friction heat are carried away anddissipated to the atmosphere. Although they arenot thought of as heat sinks, many individual partsof an automobile—such as the brake drums—arealso designed to do this important job.

AC GENERATOR(ALTERNATOR)COMPONENTSThe previous illustrations have shown the princi-ples of AC generator operation. To provide enoughdirect current for an automobile, AC generatorsmust have a more complex design. But no matterhow the design varies, the principles of operationremain the same.

The design of the AC generator limits its max-imum output. To change this maximum value fordifferent applications, manufacturers change thedesign of the stator, rotor, and other components.The following paragraphs describe the majorparts of an automotive AC generator.

RotorThe rotor carries the magnetic field. Unlike a DCgenerator, which usually has only two magneticpoles, the AC generator rotor has several north (N)and south (S) poles. This increases the number offlux lines within the AC generator and increases thevoltage output. A typical automotive rotor(Figure 8-9) has 12 poles: 6 N and 6 S. The rotorconsists of two steel rotor halves, or pole pieces,

with fingers that interlace. These fingers are thepoles. Each pole piece has either all N or all S poles.The magnetic flux lines travel between adjacent Nand S poles (Figure 8-10). Keep in mind that analternator is an AC generator; in some Europeanmanufacturers’ service manuals, the AC generator(alternator) is referred to as a generator.

Along the outside of the rotor, note that the fluxlines point first in one direction and then in the other.This means as the rotor spins inside the AC generator,the fixed conductors are being cut by flux lines, whichpoint in alternating directions. The induced voltagealternates, just as in the example of a simple AC gen-erator with only two poles. Automotive AC genera-tors may have any number of poles, as long as theyare placed N-S-N-S. Common designs use eight tofourteen poles.

The rotor poles may retain some magnetismwhen the AC generator is not in operation, but this

Figure 8-9. Rotor. (DaimlerChrysler Corporation)

Figure 8-10. The flux lines surrounding an 8-polerotor. (DaimlerChrysler Corporation)

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Figure 8-11. The magnetic field of the rotor is cre-ated by current through the rotor winding. (Reprinted bypermission of Robert Bosch GmbH)

Figure 8-12. Exploded view of the parts of the com-plete rotor assembly. (DaimlerChrysler Corporation)

residual magnetism is not strong enough to induceany voltage across the conductors. Current pro-duces the magnetic field of the rotor through therotor winding, which is a coil of wire betweenthe two pole pieces (Figure 8-11). This is also calledthe excitation winding, or the field winding.Varying the amount of field current through therotor winding varies the strength of the magneticfield, which affects the voltage output of the ACgenerator. A soft iron core is mounted inside therotor-winding (Figure 8-12). One pole piece isattached to either end of the core; when field currenttravels through the winding, the iron core is mag-netized, and the pole pieces take on the magneticpolarity of the end of the core to which they areattached. Current is supplied to the winding throughsliprings and brushes.

The combination of a soft iron rotor core andsteel rotor halves provides better localization andpermeability of the magnetic field. The rotor polepieces, winding, core, and sliprings are pressedonto a shaft. The ends of this shaft are supported bybearings in the AC generator housing. Outside thehousing, a drive pulley is attached to the shaft, asshown in Figure 8-13. A belt, driven by the enginecrankshaft-pulley, passes around the drive pulleyto turn the AC generator shaft and rotor assembly.

StatorThe three AC generator conductors are woundonto a cylindrical, laminated core. The lamina-tion prevents unwanted eddy currents from form-ing in the core. The assembled piece is called a

stator (Figure 8-14). The word stator comesfrom the word “stationary” because it does notrotate, as does the commutator conductor of a DCgenerator. Each conductor, called a stator wind-ing, is formed into a number of coils spacedevenly around the core. There are as many coilconductors as there are pairs of N-S rotor poles.Figure 8-15 shows an incomplete stator with onlyone of its conductors installed: There are sevencoils in the conductor, so the matching rotorwould have seven pairs of N-S poles, for a totalof fourteen poles. There are two ways to connectthe three-stator windings.

HousingThe AC generator housing, or frame, is made oftwo pieces of cast aluminum (Figure 8-16).Aluminum is lightweight and non-magnetic andconducts heat well. One housing piece holds abearing for the end of the rotor shaft where the

Figure 8-13. AC generator (alternator) and drive pul-ley. (DaimlerChrysler Corporation)

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Figure 8-14. An AC generator (alternator) stator.

Figure 8-15. A stator with only one conductor installed.(Delphi Automotive Systems)

Figure 8-16. AC generator (alternator) housingencloses the rotor and stator.

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Figure 8-17. AC generator (alternator) with exposedstator core.

Figure 8-18. AC generator (alternator) with the statorcore enclosed.

drive pulley is mounted. This is often called thedrive-end housing, or front housing, of the AC gen-erator. The other end holds the diodes, the brushes,and the electrical terminal connections. It alsoholds a bearing for the slipring end of the rotorshaft. This is often called the slipring-end housing,or rear housing. Together, the two pieces com-pletely enclose the rotor and the stator windings.

The end housings are bolted together. Some sta-tor cores have an extended rim that is held betweenthe two housings (Figure 8-17). Other stator coresprovide holes for the housing bolts, but do notextend to the outside of the housings (Figure 8-18).In both designs, the stator is rigidly bolted in placeinside the AC generator housing. The housing ispart of the electrical ground path because it isbolted directly to the engine. Anything connectedto the housing that is not insulated from the hous-ing is grounded.

Sliprings and BrushesThe sliprings and brushes conduct current to therotor winding. Most automotive AC generatorshave two sliprings mounted on the rotor shaft.The sliprings are insulated from the shaft andfrom each other. One end of the rotor winding isconnected to each slipring (Figure 8-19). Onebrush rides on each ring to carry current to and

from the winding. A brush holder supports eachbrush and a spring applies force to keep the brushin constant contact with the rotating slipring. Thebrushes are connected parallel with the AC gener-ator output circuit. They draw some of the ACgenerator current output and route it through therotor winding. Current through the winding mustbe DC. Field current in an AC generator is usuallyabout 1.5 to 3.0 amperes. Because the brushescarry so little current, they do not require as muchmaintenance as DC generator brushes, whichmust conduct all of the current output.

Figure 8-19. The sliprings and brushes carry currentto the rotor windings.

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Figure 8-20. Each conductor is attached to one pos-itive and one negative diode.

Figure 8-21. Positive and negative diodes may bemounted in a heat sink for protection.

For more information about generator mainte-nance, see the section on “Disassembly, Cleaning,and Inspection” in Chapter 8 of the Shop Manual.

Diode InstallationAutomotive AC generators that have three statorwindings generally use six diodes to rectify thecurrent output. The connections between the con-ductors and the diodes vary slightly, but eachconductor is connected to one positive and onenegative diode, as shown in Figure 8-20.

The three positive diodes are always insulatedfrom the AC generator housing. They are con-nected to the insulated terminal of the battery andto the rest of the automotive electrical system.The battery cannot discharge through this con-nection because the bias of the diodes blocks anycurrent from the battery. The positive diodes onlyconduct current traveling from the conductorstoward the battery.

The positive diodes are mounted together on aconductor called a heat sink (Figure 8-21). Theheat sink carries heat away from the diodes, justas the radiator carries heat away from the engine.Too much heat damages the diodes.

In the past, the three negative diodes werepressed or threaded into the AC generator rearhousing. On high-output AC generators, they maybe mounted in a heat sink for added protection.In either case, the connection to the AC generatorhousing is a ground path; the negative diodes

conduct only the current traveling from groundinto the conductors. Each group of three or morenegative or positive diodes can be called a diodebridge, a diode trio, or a diode plate. Some manu-facturers use complete rectifier assemblies con-taining all the diodes and connections on a printedcircuit board. This assembly is replaced as a unitif any of the individual components fail.

Each stator winding connects to its proper neg-ative diode through a circuit in the rectifier. Acapacitor generally is installed between the outputterminal at the positive diode heat sink to ground atthe negative diode heat sink. This capacitor is usedto eliminate voltage-switching transients at the sta-tor, to smooth out the AC voltage fluctuations, andto reduce electromagnetic interference (EMI).

CURRENTPRODUCTION INAN AC GENERATORAfter studying the principles of AC generatoroperation and its components, the total picture ofhow an automotive AC generator produces cur-rent becomes clear.

Three-Phase CurrentThe AC generator stator has three windings. Eachis formed into a number of coils, which are spacedevenly around the stator core. The voltagesinduced across each winding by one rotor revolu-tion are shown in the graphs of Figure 8-22. The

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Figure 8-22. The single-phase voltages of three con-ductors create a three-phase voltage output. (Reprintedby permission of Robert Bosch GmbH)

total voltage output of the AC generator is threeoverlapping, evenly spaced, single-phase voltagewaves, as shown in the bottom graph of the illus-tration. If the stator windings are connected into acomplete circuit, the three-phase voltages causean AC output called three-phase current.

Stator TypesWhen the three conductors are completelywound on the stator core, six loose ends remain.The way in which these ends are connected to thediode rectifier circuitry determines if the stator isa Y-type or a Delta-type (Figure 8-23). Bothkinds of stators produce three-phase current andthe rectification produces DC output. However,the voltage and current levels within the statorsdiffer.

Y-Type Stator DesignIn the Y-type stator or Y-connected stator, oneend of each of the three windings is connected at aneutral junction (Figure 8-23). The circuit diagramof the Y-type stator (Figure 8-24) looks like the let-ter Y. This is also sometimes called a wye or a starconnection. The free end of each conductor is con-nected to a positive and a negative diode.

In a Y-type stator (Figure 8-24), two windingsalways form a series circuit between a positive anda negative diode. At any given instant, the positionof the rotor determines the direction of currentthrough these two windings. Current flows fromthe negative voltage to the positive voltage. Acom-plete circuit from ground, through a negativediode, through two of the windings, and through apositive diode to the AC generator output terminal,exists throughout the 360-degree rotation of therotor. The induced voltages across the two wind-ings added together produce the total voltage at theoutput terminal. The majority of AC generators inuse today have Y-type stators because of the needfor high voltage output at low speeds.

Figure 8-23. Two types of stator windings. (Daimler-Chrysler Corporation)

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Figure 8-24. Y-type stator circuit diagram. (Daimler-Chrysler Corporation)

+

+

+

–

–

–

NEUTRAL JUNCTION

STATOR CONNECTION (1 OF 3)

CENTER TAP (SOME)

Figure 8-25. A Y-type stator circuit diagram. The centertap connects to the neutral junction of the Y-type stator ofsome AC generators. (DaimlerChrysler Corporation)

Figure 8-26. Circuit diagram of a delta-type stator.

� Unrectified AC Generators

Although the battery cannot be rechargedwith AC, other automotive accessories can bedesigned to run on unrectified alternator output.Motorola has made AC generators with sepa-rate terminals for AC output. Ford has offereda front-and-rear-window defroster that heats thewindows with three-phase, 120-volt AC. Anadditional AC generator supplies the high-voltage current. This second AC generator ismounted above the standard 12-volt AC gener-ator and driven by the same belt.

The Ford high-voltage AC generator has a Y-type stator. Field current draw is more than 4 amps, and there is no regulator in the field cir-cuit. Output is 2,200 watts at high engine speed.All of the wiring between the AC generator andthe defrosters is special, shielded wiring withwarning tags at all connectors. Ford test proce-dures use only an ohmmeter, because trying totest such high output could be dangerous.

Some AC generators include a center tap leadfrom the neutral junction to an insulated terminalon the housing (Figure 8-25). The center tap maycontrol the field current, to activate an indicatorlamp, to control the electric choke on a carbure-tor, or for other functions.

Delta-Type Stator DesignThe delta-type stator or delta-connected statorhas the three windings connected end-to-end(Figure 8-26). The circuit diagram of a delta-typestator (Figure 8-26) looks like the Greek letter delta

(�), a triangle. There is no neutral junction in adelta-type stator. The windings always form twoparallel circuit paths between one negative and twopositive diodes. Current travels through two differ-ent circuit paths between the diodes (Figure 8-27).The current-carrying capacity of the stator is doublebecause there are two parallel circuit paths. Delta-type stators are used when a high current output isneeded.

Phase RectificationThe current pattern during rectification is similar inany automotive AC generator. The only differencesare specific current paths through Y-type and delta-type stators as shown in Figures 8-27 and 8-28.

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Figure 8-27. A typical current path during rectifica-tion in a delta-type stator. (DaimlerChrysler Corporation)

Figure 8-28. A typical current path during rectifica-tion in a Y-type stator. (DaimlerChrysler Corporation)

Rectification withMultiple-Pole RotorsThe three-phase voltage output used in the exam-ples (Figure 8-29) is the voltage, which wouldresult if the rotor had only one N and one S pole.Actual AC generator rotors have many N and Spoles. Each of these N-S pairs produces one com-plete voltage sine wave per rotor revolution, acrosseach of the three windings. One complete sinewave begins at zero volts, climbs to a positive,peak, drops past zero to a negative peak, thenreturns to zero, or baseline voltage. In Figure 8-30,the sine wave voltage caused by a single pole isshown as a dashed line. The actual voltage tracefrom one winding of a 12-pole AC generator is

shown as a solid line. The entire stator output isthree of these waves, evenly spaced and overlap-ping (Figure 8-31). The maximum voltage valuefrom these waves pushes current through thediodes (Figure 8-32).

After rectification, AC generator (alternator)output is DC voltage, which is slightly lower thanthe maximum voltage peaks of the stator output.The positive portion of the AC sine wave greaterthan the DC output voltage is viewable on anoscilloscope in what is called an AC generator(alternator) ripple pattern (Figure 8-33).

Excitation Field CircuitField current through the rotor windings createsthe magnetic field of the rotor. Field current isdrawn from the AC generator output circuit once

Figure 8-29. The three-phase voltage from one revo-lution of the rotor. (Reprinted by permission of RobertBosch GmbH)

Figure 8-30. An AC generator (alternator) with sixpairs of N-S poles would produce the solid line volt-age trace. The dashed line represents an alternatorwith one pair. (Reprinted by permission of Robert BoschGmbH)

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Figure 8-31. This is the total output of a three-winding,multiple-pole AC generator.

Figure 8-32. The diodes receive the maximum volt-age values.

Figure 8-34. Some AC generators (alternators) haveadditional diodes to rectify field current. (Reprinted bypermission of Robert Bosch GmbH)

Figure 8-33. AC generator (alternator) ripple is the ACvoltage exceeding DC output voltage.

Once the AC generator has started to producecurrent, field current is drawn from the AC gen-erator output. The current may be drawn after ithas been rectified by the output diodes. Some ACgenerators draw field current from unrectifiedAC output, which is then rectified by three addi-tional diodes to provide DC to the rotor winding(Figure 8-34). These additional diodes are calledthe exciter diodes or the field diodes.

Circuit TypesAC generators (alternators) are designed with dif-ferent types of field circuits. The two most com-mon types are A-circuits and B-circuits. Circuittypes are determined by where the voltage regu-lator is connected and from where the field cur-rent is drawn.

the AC generator has begun to produce current.However, there is not enough residual magnetismin the rotor poles to induce voltage during startup. An AC generator cannot start operation inde-pendently. Field current must be drawn fromanother source in order to magnetize the rotor andbegin AC generator output.

The other source is the vehicle battery con-nected to the rotor winding through the excita-tion, or field, circuit. Battery voltage “excites”the rotor magnetic field and begins output.When the engine is off, the battery must be dis-connected from the excitation circuit. If not, itcould discharge through the rotor windings toground. Some AC generators use a relay to con-trol this circuit. Other systems use the voltageregulator or a part of the ignition switch to con-trol the excitation circuit.

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ALTERNATOR

REGULATOR

IGN

F

SWITCH

SENSINGVOLTAGE

Figure 8-35. An A-circuit. (Regulator is after the field.)

A-CircuitThe A-circuit AC generator (Figure 8-35) is alsocalled an externally grounded field AC generator.Both brushes are insulated from the AC generatorhousing. One brush connects to the voltage regu-lator, where it is grounded. The second brush con-nects to the output circuit within the AC generator,where it draws current for the rotor winding. Theregulator connects between the rotor field windingand ground. This type of circuit is often used withsolid-state regulators, which are small enough tobe mounted on the AC generator housing.

B-CircuitThe B-circuit AC generator (Figure 8-36) is alsocalled an internally grounded field AC generator.One brush is grounded within the AC generatorhousing. The other brush is insulated from thehousing and connected through the insulated volt-age regulator to the AC generator output circuit.The rotor field winding is between the regulatorand ground. This type of circuit is most often usedwith electromagnetic voltage regulators, whichare mounted away from the AC generator housing.

Self-Regulation of CurrentThe maximum current output of an AC generator islimited by its design. As induced voltage causescurrent to travel in a conductor, a counter-voltage isalso induced in the same conductor. The counter-voltage is caused by the expanding magnetic fieldof the original induced current. The counter-voltagetends to oppose any change in the original current.

The more current the AC generator puts out, thegreater this counter-voltage becomes. At a certainpoint, the counter-voltage is great enough to com-

pletely stop any further increase in the AC genera-tor’s current output. At this point, the AC generatorhas reached its maximum current output. Therefore,because the two voltages continue to increase as ACgenerator speed increases, a method of regulatingAC generator voltage is required.

For more information about testing AC gener-ators, see the following sections in Chapter 8 ofthe Shop Manual: “Testing Specific Models,”“Unit Removal,” “Disassembly, Cleaning, andInspection,” and “Bench Tests.”

VOLTAGEREGULATIONAC generator regulators limit voltage output by con-trolling field current. The location of the regulator inthe field circuit determines whether the AC genera-tor is an A-circuit or a B-circuit. Voltage regulatorsbasically add resistance to field current in series.

AC generator output voltage is directly relatedto field strength and rotor speed. An increase ineither factor increases voltage output. Similarly, adecrease in either factor decreases voltage output.Rotor speed is controlled by engine speed and can-not be changed simply to control the AC generator.Controlling the field current in the rotor windingcan change field strength; this is how AC generatorvoltage regulators work. Figure 8-37 shows howthe field current (dashed line) is lowered to keepAC generator output (solid line) at a constant max-imum, even when the rotor speed increases.

At low rotor speeds, the field current is at fullstrength for relatively long periods of time, and isreduced only for short periods (Figure 8-38A).This causes a high average field current. At high

Figure 8-36. A B-circuit. (Regulator is before the field.)

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162 Chapter Eight

Figure 8-37. Field current is decreased as rotor speedincreases, to keep AC generator (alternator) output volt-age at a constant level.

Figure 8-38. The field current flows for longer peri-ods of time at low speeds (t1) than at high speeds (t2).(Reprinted by permission of Robert Bosch GmbH)

Figure 8-39. Most regulators use a multiple-plug con-nector to ensure connections are properly made.(Reprinted by permission of Robert Bosch GmbH)

rotor speeds, the field current is reduced for longperiods of time and is at full strength only forshort periods (Figure 8-38B). This causes a lowaverage field current.

On older vehicles, an electromagnetic regulatorcontrolled the field circuit. However, in the 1970s,semiconductor technology made solid-state volt-age regulators possible. Because they are smallerand have no moving parts, solid-state regulatorsreplaced the older electromagnetic types in ACcharging systems. On newer vehicles, the solid-state regulator may be a separate component built

into the AC generator or incorporated into thepowertrain control module (PCM).

Some solid-state regulators are mounted on theinside or outside of the AC generator housing.Remotely mounted voltage regulators often use amultiple-plug connector (Figure 8-40) to ensureall connections are properly made. This elimi-nates exposed wiring and connections, which areprone to damage.

ELECTROMAGNETICREGULATORSElectromagnetic voltage regulators, sometimescalled electromechanical regulators, operate thesame whether used with old DC generators ormore common AC generators. The electromag-netic coil of the voltage regulator is connectedfrom the ignition switch to ground. This forms aparallel branch receiving system voltage, eitherfrom the AC generator output circuit or from thebattery. The magnetic field of the coil acts uponan armature to open and close contact points con-trolling current to the field.

Double-Contact VoltageRegulatorAt high rotor speeds, the AC generator may beable to force too much field current through asingle-contact regulator and exceed the desiredoutput. This is called voltage creep, or voltagedrift. Single-contact regulators are used only withlow-current-output alternators. Almost all electro-magnetic voltage regulators used with automotive

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Figure 8-40. The circuit diagram of a double-contactregulator. (Delphi Automotive Systems)

AC generators are double-contact units (Figure 8-40).When the first set of contacts opens at lower rotorspeeds, current passes through a resistor wired inseries with the field circuit. These contacts are

called the series contacts. The value of the regulat-ing resistor is kept very low to permit high fieldcurrent when needed. At higher rotor speeds, thecoil further attracts the armature and a second setof contacts is closed. This grounds the field circuit,stopping the field current. These contacts are calledthe shorting contacts because they short-circuit thefield to ground. The double-contact design offersconsistent regulation over a broad range of ACgenerator speeds.

SOLID-STATEREGULATORSSolid-state regulators completely replaced theolder electromagnetic design on late-model vehi-cles. They are compact, have no moving parts,and are not seriously affected by temperaturechanges. The early solid-state designs combinetransistors with the electromagnetic field relay.The latest and most compact is the integrated cir-cuit (IC) regulator (Figure 8-41). This combinesall control circuitry and components on a single

Figure 8-41. An example of the latest integrated circuit regulator design, a Ford IARregulator and brush holder.

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164 Chapter Eight

Figure 8-42. Circuit diagram of a typical solid-statevoltage regulator. (Delphi Automotive Systems)

silicon chip. Attaching terminals are added andthe chip is sealed in a small plastic module thatmounts inside, or on the back of, the AC genera-tor. Because of their construction, however, allsolid-state regulators are non-serviceable andmust be replaced if defective. No adjustments arepossible.

Here is a review of most components of asolid-state regulator:

• Diodes• Transistors• Zener diodes• Thermistors• Capacitors

Diodes are one-way electrical check valves.Transistors act as relays. AZener diode is speciallydoped to act as a one-way, electrical check valveuntil a specific reverse voltage level is reached. Atthat point, the Zener diode allows reverse currentto pass through it.

The electrical resistance of a thermistor, or ther-mal resistor, changes as temperature changes. Mostresistors used in automotive applications are callednegative temperature coefficient (NTC) resistorsbecause their resistance decreases as temperatureincreases. The thermistor in a solid-state regulatorreacts to temperature to ensure proper batterycharging voltage. Some manufacturers, in order tosmooth out any abrupt voltage surges and protectthe regulator from damage, use a capacitor. Diodesmay also be used as circuit protection.

General Regulator OperationFigure 8-42 is a simplified circuit diagram of asolid-state regulator. This A-circuit regulator is con-tained within the housing. Terminal 2 on the ACgenerator is always connected to the battery, butbattery discharge is limited by the high resistance ofR2 and R3. The circuit allows the regulator to sensebattery voltage.

When the ignition switch is closed in the circuitshown in Figure 8-43, current travels from the bat-tery to ground through the base of the TR1 tran-sistor. This causes the transistor to conduct currentthrough its emitter-collector circuit from the bat-tery to the low-resistance rotor winding, whichenergizes the AC generator field and turns on thewarning lamp. When the AC generator begins toproduce current (Figure 8-44), field current isdrawn from unrectified AC generator outputand rectified by the diode trio, which is charging

voltage. The warning lamp is turned off by equalvoltage on both sides of the lamp.

When the AC generator has charged the batteryto a maximum safe voltage level (Figure 8-45),the battery voltage between R2 and R3 is highenough to cause Zener diode D2 to conduct inreverse bias. This turns on TR2, which shorts thebase circuit of TR1 to ground. When TR1 isturned off, the field circuit is turned off at theground control of TR1.

With TR1 off, the field current decreases andsystem voltage drops. When voltage drops lowenough, the Zener diode switches off and current isno longer applied to TR2. This opens the field cir-cuit ground and energizes TR1. TR1 turns back on.The field current and system voltage increase. Thiscycle repeats many times per second to limit theAC generator voltage to a predetermined value.

The other components within the regulator per-form various functions. Capacitor C1 provides

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Figure 8-43. Field current in a typical solid-state reg-ulator during starting. (Delphi Automotive Systems)

stable voltage across resistor R3. Resistor R4 pre-vents excessive current through TR1 at high tem-peratures. To prevent circuit damage, diode D3bypasses high voltages induced in the field wind-ings when TR1 turns off. Resistor R2 is a ther-mistor, which causes the regulated voltage to varywith temperature. R5 allows the indicator lamp toturn off if the field circuit is open.

For more information about voltage regulators,see the “Voltage Regulator Service Section” inChapter 8 of the Shop Manual.

Specific Solid-State RegulatorDesignsGM Delco-Remy (Delphi)The Delco-Remy solid-state automotive regulatoris used in Figures 8-43 to 8-46 to explain the basic

operation of these units. This is the integral regu-lator unit of the SI series AC generators. The 1 and2 terminals on the housing connect directly to theregulator. The 1 terminal conducts field currentfrom the battery or the AC Generator (alternator)and controls the indicator lamp. The 2 terminalreceives battery voltage and allows the Zenerdiode to react to it.

Unlike other voltage regulators, the multifunc-tion IC regulator used with Delco-Remy CS-seriesAC generators (Figure 8-46) switches the fieldcurrent on and off at a fixed frequency of 400 Hz(400 times per second). The regulator varies theduty cycle, or percentage of on time to total cycletime, to control the average field current and toregulate voltage. At high speeds, the on time mightbe 10 percent with the off time 90 percent. At lowspeeds with high electrical loads, this ratio couldbe reversed: 90 percent on time and 10 percent offtime. Unlike the SI series, CS AC generators have

Figure 8-44. Field current drawn from AC generator(alternator) output. (Delphi Automotive Systems)

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166 Chapter Eight

Figure 8-45. When AC generator (alternator) outputvoltage reaches a maximum safe level, no current isallowed in the rotor winding. (Delphi Automotive Systems)

Figure 8-46. GM CS AC generator (alternator) regu-lator circuit. (Delphi Automotive Systems)

no test hole to ground the regulator for full-fieldtesting. The regulator cannot be tested with anohmmeter; a special tester is required.

MotorcraftAt one time, Motorcraft AC generators used bothremote-mounted and integral solid-state regula-tors. Motorcraft regulator terminals are desig-nated as follows:

• A� or A� connects the battery to the fieldrelay contacts.

• S� connects the AC generator output to thefield relay coil.

• F� connects the field coil to the regulatortransistors.

• I� connects the ignition switch to the fieldrelay and regulator contacts (only on vehi-cles with a warning lamp).

Ford began using a remote-mounted, fully solid-state regulator on its intermediate and large mod-els in 1978. The functions of the I, A�, 8, and Fterminals are identical to those of the transis-torized regulator. On systems with an ammeter,the regulator is color coded blue or gray, and theT terminal is not used. On warning lamp systems,the regulator is black, and all terminals can beused. The two models are not interchangeable,and cannot be substituted for the earlier solid-state unit with a relay or for an electromagneticregulator. However, Ford does provide red orclear service replacement solid-state regulators,which can be used with both systems.

The Motorcraft integral alternator/regulator(JAR) introduced in 1985 uses an IC regulator,which is also mounted on the outside of the rearhousing. This regulator differs from others becauseit contains a circuit indicating when the battery isbeing overcharged. It turns on the charge indicatorlamp if terminal A voltage is too high or too low, orif the terminal 8 voltage signal is abnormal.

DaimlerChryslerThe DaimlerChrysler solid-state regulator dependson a remotely mounted field relay to open andclose the isolated field or the A-circuit AC genera-tor field. The relay closes the circuit only when theignition switch is turned on. The voltage regulator(Figure 8-47) contains two transistors that areturned on and off by a Zener diode. The Zenerdiode reacts to system voltage to start and stop field

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Figure 8-47. DaimlerChrysler solid-state voltage reg-ulator. (DaimlerChrysler Corporation)

current. The field current travels through whatDaimlerChrysler calls a field-suppression diode,which limits current to control AC generator out-put. The regulator also contains a thermistor tocontrol battery charging voltage at various temper-atures. The regulator has two terminals: One isconnected to the ignition system; the other is con-nected to the alternator field.

Computer-ControlledRegulationDaimlerChrysler Corporation eliminated the sepa-rate regulator by moving its function to the pow-ertrain control module (PCM) in 1985. When theignition is turned on, the PCM logic module or logiccircuit checks battery temperature to determine thecontrol voltage (Figure 8-48). A pre-driver transis-tor in the logic module or logic circuit then signalsthe power module or power circuit driver transistorto turn the AC generator current on (Figure 8-49).The logic module or logic circuit continually mon-itors battery temperature and system voltage. At thesame time, it transmits output signals to the powermodule or power circuit driver to adjust the fieldcurrent as required to maintain output between 13.6and 14.8 volts. Figure 8-50 shows the complete cir-cuitry involved.

General Motors has taken a different approachto regulating CS charging system voltage elec-tronically. Turning the ignition switch on sup-plies voltage to activate a solid-state digitalregulator, which uses pulse-width modulation(PWM) to supply rotor current and thus controloutput voltage. The rotor current is proportionalto the PWM pulses from the digital regulator.

With the ignition on, narrow width pulses aresent to the rotor, creating a weak magnetic field.As the engine starts, the regulator senses AC gen-erator rotation through AC voltage detected on aninternal wire. Once the engine is running, theregulator switches the field current on and off ata fixed frequency of about 400 cycles per second(400 Hz). By changing the pulse width, or on-offtime, of each cycle, the regulator provides acorrect average field current for proper systemvoltage control.

A lamp driver in the digital regulator controlsthe indicator warning lamp, turning on the bulbwhen it detects an under- or over-voltage condi-tion. The warning lamp also illuminates if the ACgenerator is not rotating. The PCM does notdirectly control charging system voltage, as in theDaimlerChrysler application. However, it doesmonitor battery and system voltage through anignition switch circuit. If the PCM reads a voltageabove 17 volts, or less than 9 volts for longer than

Figure 8-48. DaimlerChrysler solid-state voltage reg-ulator. (DaimlerChrysler Corporation)

Figure 8-49. Battery temperature circuit of the Daimler-Chrysler computer regulated charging system. (Daimler-Chrysler Corporation)

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168 Chapter Eight

Figure 8-51. GM ammeter. (GM Service and PartsOperations)10 seconds, it sets a code 16 in memory and turns

on the malfunction indicator lamp (MIL).

Diagnostic Trouble Codes (DTC)On late-model DaimlerChrysler vehicles, theonboard diagnostic capability of the engine con-trol system detects charging system problems andrecords up to five diagnostic trouble codes (DTC)in the system memory. Some of the codes light aMIL on the instrument panel; others do not.Problems in the General Motors CS charging sys-tem cause the PCM to turn on the indicator lampand set a single code in memory.

CHARGE/VOLTAGE/CURRENTINDICATORSA charging system failure cripples an automobile.Therefore, most manufacturers provide some wayfor the driver to monitor the system operation.The indicator may be an ammeter, a voltmeter, oran indicator lamp.

AmmeterAn instrument panel ammeter measures charg-ing system current into and out of the battery andthe rest of the electrical system (Figure 8-51).The ammeter reads the voltage drop of the cir-cuit. When current is traveling from the AC gen-erator into the battery, the ammeter moves in apositive or charge direction. When the batterytakes over the electrical system’s load, currenttravels in the opposite direction and the nee-dle moves into the negative, or discharge, zone.The ammeter simply indicates which is doingthe most work in the electrical system, the bat-tery or the AC generator (alternator). Someammeters are graduated to indicate the approxi-mate current in amperes, such as 5, 10, or 20.Others simply show an approximate rate ofcharge or discharge, such as high, medium, orlow. Some ammeters have a resistor parallel sothe meter does not carry all of the current, theseare called shunt ammeters. While the ammetertells the driver whether the charging system isfunctioning normally, it does not give a goodpicture of the battery condition. Even when theammeter indicates a charge, the current output

Figure 8-50. DaimlerChrysler computer-regulatedcharging system internal field control. (DaimlerChryslerCorporation)

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Figure 8-52. Automotive voltmeter in instrument panel.

may not be high enough to fully charge the bat-tery while supplying other electrical loads.

VoltmeterThe instrument panels of many late-model vehi-cles contain a voltmeter instead of an ammeter(Figure 8-52). A voltmeter measures electricalpressure and indicates regulated generator volt-age output or battery voltage, whichever isgreater. System voltage is applied to the meterthrough the ignition switch contacts. Figure 8-53shows a typical voltmeter circuit.

The voltmeter tells a driver more about thecondition of the electrical system of a vehicle thanan ammeter. When a voltmeter begins to indicatelower-than-normal voltage, it is time to check thebattery and the voltage regulator.

Indicator LampsMost charging systems use an instrument panelindicator, or warning lamp, to show general

charging system operation. Although the lampusually does not warn the driver of an over-charged battery or high charging voltage, it lightsto show an undercharged battery or low voltagefrom the AC generator.

The lamp also lights when the battery suppliesfield current before the engine starts. The lamp isoften connected parallel to a resistor; therefore,field current travels even if the bulb fails. Thelamp is wired so it lights when battery currenttravels through it to the AC generator field. Whenthe alternator begins to produce voltage, this volt-age is applied to the side of the lamp away fromthe battery. When the two voltages are equal, novoltage drops are present across the lamp and itgoes out. When indicator lamps are used, the reg-ulator must be able to monitor when the AC gen-erator is charging. One method is to use “stator”or neutral voltage. This signal is present onlywhen the AC generator is charging, and is one-half of charging voltage. When stator voltage isabout three volts, it energizes a relay to open theindicator lamp ground circuit (Figure 8-53).

Figure 8-54 shows a typical warning lamp cir-cuit installation. In figure 9-14, a 500-ohm resis-tor is used for warning lamp systems and a 420-ohm resistor for electronic display clusters. InFigure 8-54, a 40-ohm resistor (R5) is installednear the integral regulator. In each case, thegrounded path ensures the warning lamp lights ifan open occurs in the field circuitry.

As previously discussed, indicator lamps canalso be controlled by the field relay. The indicatorlamp for a Delco-Remy CS system works differ-ently than most others. It lights if charging volt-age is either too low or too high. Any problem inthe charging system causes the lamp to light atfull brilliance.

Figure 8-53. A typical voltmeter circuit.

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170 Chapter Eight

Figure 8-54. GM warning lamp circuit. (GM Service andParts Operations)

Figure 8-55. GM fusible links.

CHARGING SYSTEMPROTECTIONIf a charging system component fails or malfunc-tions, excessive current or heat, voltage surges,and other uncontrolled factors could damagewiring and other units in the system. To protectthe system from high current, fusible links are of-ten wired in series at various places in the cir-cuitry. Figure 8-55 shows some typical fusiblelink locations.

COMPLETE ACGENERATOROPERATIONWhen the ignition is first switched from off to on,before cranking the engine, a charge lamp comeson. This indicates, of course, that the AC genera-tor is not generating a voltage. At the same time,battery voltage is applied to the rotor coil so thatwhen the rotor begins to spin, the magnetic fieldscut across the stator windings and produce current(Figure 8-56).

After the engine starts, the rotor is spinning fastenough to induce current from the stator. The cur-rent travels through the diodes and out to the bat-tery and electrical system (Figure 8-57). Once theIC regulator senses system voltage is greater than

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battery voltage, it redirects current to switch offthe charge lamp.

During normal operation, AC generator voltageexceeds the typically specified 14.5 volts at times.To protect the battery and delicate components inthe electrical system, the IC regulator shuts off cur-rent to the rotor, cutting AC generator output to zero(Figure 8-58). Note that even though the AC gener-ator is momentarily “turned off,” the charge lampdoes not come on. Within a split second, the IC reg-ulator re-energizes the rotor again once output fallsbelow the minimum. The IC regulator switches bat-tery voltage on and off this way to control outputand maintain system voltage at an ideal level.

AC GENERATOR(ALTERNATOR)DESIGNDIFFERENCESOriginal equipment manufacturers (OEM) usevarious AC generator designs for specific applica-tions. It has been noted that such factors as maxi-

mum current output and field circuit types affectAC generator construction. The following para-graphs describe some commonly used automotiveAC generators.

Delphi (Delco-Remy) GeneralMotors ApplicationsDelphi, formerly the Delco-Remy division ofGeneral Motors Corporation, is now a separatecorporation that supplies most of the electricaldevices used on GM vehicles, as well as those ofsome other manufacturers. The trademark namefor Delco-Remy alternators was Delcotron gener-ators. The alternator model number and currentoutput can be found on a plate attached to, orstamped into, the housing.

DN-SeriesThe 10-DN series AC generator or alternatoruses an external electromagnetic voltage regu-lator. Six individual diodes are mounted in therear housing (Figure 8-59) with a capacitor forprotection. A 14-pole rotor and Y-type stator

MONOLITHICINTEGRATEDCIRCUIT

IC REGULATOR

ROTOR COIL

STATOR COIL

B

B IG

IG

IGN.S/W

CHARGELAMP

E

E

S S

L LTr1

Tr3

Tr2

F

P

Figure 8-56. When AC generator voltage is too high, the regulator momentarily cuts off current to the rotor coils, elim-inating the magnetic field. The rotor continues to spin, but no voltage is generated. (Reprinted by permission of ToyotaMotor Corporation)

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172


IC REGULATOR

ROTOR COIL

STATOR COIL

B

B IG

IG

IGN.S/W

CHARGELAMP

E

E

S S

L LTR1

TR3

TR2

F

P

Figure 8-57. When the ignition is on and the engine is not running, the regulator energizes the rotor coil to builda magnetic field in the stator. The regulator turns on the charge light, indicating that the AC generator is not gener-ating a voltage. (Reprinted by permission of Toyota Motor Corporation)


IC REGULATOR

ROTOR COIL

STATOR COIL

B

B IG

IG

IGN.S/W

CHARGELAMP

E

E

S S

L LTR1

TR3

TR2

F

P

Figure 8-58. After the engine is running, the AC generator generates a voltage greater than the battery. Thecharge light goes out, indicating normal operation. (Reprinted by permission of Toyota Motor Corporation)

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provide current output. Field current is drawn fromrectified output and travels through a B-circuit.The terminals on a 10-DN are labeled BAT, GRD,R, and F. If the AC generator is used with an ex-ternal electromagnetic regulator, the followingapplies:

• BAT connects AC generator output to theinsulated terminal of the battery.

• GRD, if used, is an additional ground path.• R, if used, is connected to a separate field

relay controlling the indicator lamp.• F connects the rotor winding to the voltage

regulator.

Some 10-DN alternators are used with aremotely mounted solid-state regulator. The volt-age control level of this unit is usually adjustable.The terminal connections are the same for elec-tromagnetic and solid-state regulators.

SI SeriesThe 10-SI series AC generator uses an internallymounted voltage regulator and came into use inthe early 1970s. The most common early modelDelcotron alternators are part of the SI series andinclude models 10, 12, 15, and 27 as shown inFigure 8-60. A 14-pole rotor is used in most mod-els. The 10-SI and 12-SI models have Y-type

stators, and the 15-SI and 27-SI models havedelta-type stators. Two general SI designs havebeen used, with major differences appearing inthe rear housing diode installation, regulatorappearance, field circuitry, and ground path.

Most SI models have a rectifier bridge thatcontains all six rectifying diodes (Figure 8-61).The regulator is a fully enclosed unit attached byscrews to the housing. Field current is drawnfrom unrectified AC generator output and recti-fied by an additional diode trio. All SI modelshave A-circuits, their terminals are labeled BAT,No. 1, and No. 2.

• The BAT terminal connects AC generatoroutput to the insulated terminal of the battery.

• The No. 1 terminal conducts battery currentto the rotor winding for the excitation circuitand is connected to the indicator lamp.

• The No. 2 terminal receives battery voltageso the voltage regulator can react to systemoperating conditions.

All SI models have a capacitor installed in the rearhousing to protect the diodes from sudden voltagesurges and to filter out voltage ripples that couldproduce EMI. The 27-SI, which is inten-ded principally for commercial vehicles, has anadjustable voltage regulator (Figure 8-62). Thevoltage is adjusted by removing the adjustmentcap, rotating it until the desired setting of low,

Figure 8-59. A 10-SI series AC generator (alternator).(Delphi Automotive Systems)

Figure 8-60. A 10-SI series AC generator [Delcotron].(Delphi Automotive Systems)

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174 Chapter Eight

Figure 8-63. Typical Delco-Remy CS series AC gener-ator (alternator) construction. (Delphi Automotive Systems)

medium, medium-high, or high is opposite the ar-row on the housing, and reinstalling it in the newposition. Repair or replace a 27-SI AC generatoronly if it fails to pass an output test after the reg-ulator has been adjusted.

CS SeriesThe smaller Delco-Remy CS series AC generatorsintroduced on some 1986 GM cars (Figure 8-63)maintain current output similar to larger ACgenerators. This series includes models CS-121,CS-130, and CS-144. The number following theCS designation denotes the outer diameter of thestator lamination in millimeters. All models use adelta-type stator. Field current is taken directlyfrom the stator, eliminating the field diode trio.An integral cooling fan is used on the CS-121 andCS-130.

Electronic connections on CS AC generatorsinclude a BAT output terminal and either a one- ortwo-wire connector for the regulator. Figure 8-64shows the two basic circuits for CS AC generators,but there are a number variations. Refer to thevehicle service manual for complete and accuratecircuit diagrams. The use of the P, F, and S termi-nals is optional.

• The P terminal, connected to the stator, maybe connected to a tachometer or other suchdevice.

• The F terminal connects internally to fieldpositive and may be used as a fault indicator.

• The S terminal is externally connected tobattery voltage to sense the voltage to becontrolled.

Figure 8-61. The rear end housing of the later-model10-SI. (Delphi Automotive Systems)

Figure 8-62. The Delco 27-SI alternator has anadjustable voltage regulator. (Delphi Automotive Systems)

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terminal or side-terminal AC generator. Thesecharging systems are called external voltage reg-ulator (EVR) systems to differentiate them fromintegral alternator/regulator (IAR) systems.

Integral Alternator/Regulator ModelsThe Motorcraft IAR AC generators are rated at 40to 80 amperes. The sealed rectifier assembly is at-tached to the slipring-end housing. On early mod-els, the connecting terminals (BAT and STA) pro-truded from the side of the AC generator in aplastic housing. Current models use a single pinstator (STA) connector and separate output stud(BAT). The brushes are attached to, and removedwith, the regulator. A Y-type stator is used with a12-pole rotor. Some applications have an internalcooling fan.

Turning the ignition on sends voltage to theregulator I terminal through a resistor in the cir-cuit. System voltage is sensed and field current isdrawn through the regulator A terminal until theignition is turned off, which shuts off the controlcircuit.

If the vehicle has a heated windshield, output isswitched from the battery to the windshield by anoutput control relay. This allows output voltage toincrease above the normal regulated voltage andvary with engine speed. The regulator I circuitlimits the increase to 70 volts, which is controlledby the heated windshield module during the ap-proximate four-minute cycle of heated windshieldoperation. When the cycle times out, the chargingsystem returns to normal operation.

DaimlerChryslerDaimlerChrysler Corporation manufactured all of theAC generators for its domestic vehicles until the late1980s, when it phased in Bosch and Nippondenso ACgenerators for use on all vehicles.

DaimlerChrysler used two alternator designsfrom 1972 through 1984. The standard-duty alter-nator, rated from 50 to 65 amperes, is identifiedby an internal cooling fan and the stator coreextension between the housings. The heavy-duty100-ampere alternator has an external fan and atotally enclosed stator core. Identification also isstamped on a color-coded tag on the housing.

All models have a 12-pole rotor and use aremotely mounted solid-state regulator. The brushescan be replaced from outside the housing. Individualdiodes are mounted in positive and negative heat

• The L terminal connects the regulator to theindicator lamp and battery.

The indicator lamp in a CS charging systemworks differently than in other Delco-Remy sys-tems: Any defect causes it to light at full bril-liance. The lamp also lights if charging voltage iseither too low or too high. If the regulator has anI terminal, its wire supplies field current in addi-tion to that applied internally, either directly fromthe switch or through a resistor.

MotorcraftMotorcraft, a division of Ford Motor Company,makes most of the AC generators used on domes-tic Ford vehicles. Model and current rating iden-tifications for later models are stamped on thefront housing with a color code. Motorcraft ACgenerators prior to 1985 are used with either anelectromechanical voltage regulator or a remotelymounted solid-state regulator. One exception tothis is the 55-ampere model of 1969–1971, whichhas a solid-state regulator mounted on the rearhousing. This model has an A-circuit; all othersare B-circuit. The Motorcraft integral alterna-tor/regulator (IAR) model was introduced onsome front-wheel drive Ford models in 1985.This AC generator (alternator) has a solid-stateregulator mounted on its rear housing. SomeMotorcraft charging systems continue to use anexternal solid-state regulator with either a rear-

Figure 8-64. Two basic circuits for CS AC generators(alternator). (Delphi Automotive Systems)

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176 Chapter Eight

GROUND TERMINAL FIELD TERMINALS

FIELD TERMINAL (VOLT-REG)

FIELD TERMINAL (IGNITION SWITCH)

BATTERY OUTPUTTERMINAL

Figure 8-66. The terminals on a 100-amp Daimler-Chrysler AC generator (alternator). (DaimlerChryslerCorporation)

sink assemblies, and are protected by a capacitor.The terminals on the standard-duty AC generator arelabeled BAT, GRD, and FLD (Figure 8-65).

• The BAT terminal connects AC generator out-put to the insulated terminal of the battery.

• The GRD terminal is the ground connection.• The FLD terminals connect to the insulated

brushes. On the 100-ampere model, the FLDterminal has two separate prongs that fit intoa single connector (Figure 8-66). The addi-tional GRD terminal is a ground path.

DaimlerChrysler standard-duty AC generatorshave a Y-type stator connected to six diodes.Although both brush holders are insulated fromthe housing, one is indirectly grounded throughthe negative diode plate, making it a B-circuit.The 100-ampere AC generator has a delta-typestator. Each of the conductors is attached to twopositive and two negative diodes. These 12 diodescreate additional parallel circuit branches forhigh-current output.

DaimlerChrysler eliminated the use of a separatevoltage regulator on most 1985 and later fuel in-jected and turbocharged engines by incorporatingthe regulator function into the powertrain controlmodule (PCM), as shown in Figure 8-67.

The computer-controlled charging system wasintroduced with the standard DaimlerChrysler ACgenerator on GLH and Shelby turbo models. Allother four-cylinder engines used either a newDaimlerChrysler 40/90-ampere AC generator or a

modified Bosch 40/90-ampere or 40/100-amperemodel.

The DaimlerChrysler-built AC generatoruses a delta-type stator. The regulator circuit isbasically the isolated-field type, but field cur-rent is controlled by integrated circuitry inthe logic and power modules (Figure 8-68) orthe logic and power circuits of the single-module engine control computer (SMEC) orsingle-board engine control computer (SBEC).In addition to sensing system voltage, the logicmodule or circuit senses battery temperature asindicated by system resistance. The computerthen switches field current on and off in a duty

Figure 8-65. The terminals on a DaimlerChrysler standard-duty AC generator (alternator). (Daimler-Chrysler Corporation)

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Figure 8-67. Typical DaimlerChrysler computer volt-age regulation with DaimlerChrysler 40/90-ampere ACgenerator (alternator). Circuit connections vary on dif-ferent models. (DaimlerChrysler Corporation)

cycle that regulates charging voltage, as in anyother system. The DaimlerChrysler computer-controlled charging system has the followingimportant features:

• It varies charging voltage relative to ambi-ent temperature and the system voltagerequirements.

• A self-diagnostic program can detect charg-ing system problems and record fault codesin system memory. Some codes will lightthe POWER LOSS, POWER LIMITED, orMALFUNCTION INDICATOR lamp onthe instrument panel; others will not.

Turning the ignition on causes the logic circuitto check battery temperature to determine thecontrol voltage. A predriver transistor in the logicmodule or logic circuit signals a driver translatorin the power module or power circuit to turn onthe AC generator field current (Figure 8-68). Thelogic module or logic circuit constantly monitorssystem voltage and battery temperature and sig-nals the driver in the power module or power cir-cuit when field current adjustment is necessary tokeep output voltage within the specified 13.6-to-14.8-volt range.

Figure 8-68. DaimlerChrysler computer-regulated charging system internal field control. (DaimlerChrysler Corporation)

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Figure 8-70. Nippondenso and Bosch AC genera-tors used on DaimlerChrysler vehicles have identicalconnections. (DaimlerChrysler Corporation)

Bosch AC Generators (Alternators)Modified Bosch 40/90-ampere and 40/l00-ampereAC generators (alternators) were introduced in1985 for use with the DaimlerChrysler computer-controlled charging system. These Bosch dual-output AC generators have a Y-type stator andwere modified by removing their internal voltageregulators and changing the external leads. Theyare fully interchangeable with DaimlerChryslerdual-output AC generators of the same rating. Useof dual-output AC generators was phased out infavor of a single-output Bosch alternator whenDaimlerChrysler ceased manufacture of its ownalternators in 1989. Current DaimlerChryslercharging systems with a Bosch AC generator (84or 86 amperes) are essentially the same design asthose used with the dual-output AC generators(Figure 8-69). However, an engine controllerreplaces the separate logic and power modules.

Nippondenso AC GeneratorsSome current DaimlerChrysler vehicles useNippondenso AC generators with an output rangeof 68 to 102 amperes. These are virtual clones ofthe Bosch design, even to the external wiring con-nections (Figure 8-70). Charging system circuitryis the same, as are test procedures.

Import Vehicle ChargingSystemsMany European vehicles have Bosch AC genera-tors featuring Y-type stators. Bosch models with aremote regulator use six rectifiers and have athreaded battery terminal and two-way spade con-nector on the rear housing. Those with an integralregulator contain 12 rectifiers and have a threadedbattery stud marked B� and a smaller threadedstud marked D�. This smaller stud is used forvoltage from the ignition switch. Models with in-ternal regulators also have a diode trio to supplyfield current initially and a blocking diode toprevent current from flowing back to the ignitionsystem when the ignition is turned off.

Several manufacturers such as Hitachi,Nippondenso, and Mitsubishi provide AC gener-ators for Japanese vehicles. While all functionon the same principles just studied, the designand construction of some units are unique. Forexample, Figure 8-71 shows a Mitsubishi ACgenerator that uses an integral regulator withdouble Y-stator and 12 diodes in a pair of recti-fier assemblies to deliver high current with highvoltage at low speeds. A diode trio internallysupplies the field, and a 50-ohm resistor in theregulator performs the same function as theBosch blocking diode.

Figure 8-69. Current DaimlerChrysler charging sys-tem. (DaimlerChrysler Corporation)

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SUMMARYThe sine wave voltage induced across one ACgenerator (alternator) conductor generates single-phase current. By connecting the AC generatorconductor diodes, the AC is fully rectified to DC.In an actual automotive AC generator, there aremore than two magnetic poles and one conduc-tor. Common AC generators have from 8 to 14poles on a rotor, and three conductors wound tocreate a stator. The rotor and stator are held in atwo-piece housing. Two brushes attached to thehousings, but often insulated from it, ride onsliprings to carry current to the rotor winding.The diodes are installed in the same end housingas the brushes. Three positive diodes are insu-lated from the housing; three negative diodes aregrounded to the housing

Stators with three conductors produce three-phase current. The three conductors may be con-nected to make a Y-type or a delta-type stator. Therectification process is the same for both types,although the current paths through the stators dif-fer. Rectified output from a multiple-pole ACgenerator is a rippling DC voltage.

Because the rotor does not retain enough mag-netism to begin induction, an excitation circuitmust carry battery current to the rotor winding. Therotor winding is part of an externally groundedfield, or A-circuit; or an internally grounded field,or B-circuit.

Because a counter-voltage is induced in the sta-tor windings, AC generator current output is self-limiting. Voltage regulation is still needed. Thosewith integrated circuits have replaced electromag-netic voltage regulators. Voltage regulators now inuse are completely solid-state designs. They replacedthe electromagnetic type regulators in AC chargingsystems because they are smaller and have no mov-ing parts. Because of the construction of solid-stateregulators, they are non-serviceable and must be re-placed if defective. Their function is the same: tocontrol AC generator output by modulating currentthrough the field windings of the AC generator.

Indicators allow the driver to monitor the per-formance of the charging system: These includeammeters, voltmeters, or warning lamps. Anammeter measures the charging system currentinto and out of the battery and the entire electri-cal system. A voltmeter measures electrical

Figure 8-71. Mitsubishi charging system. (Mitsubishi)

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pressure and indicates regulated AC generatorvoltage output or battery voltage. Indicatorlamps illuminate on the instrument panel of thevehicle and indicate to the driver general charg-ing system operation status.

Wiring and other components in the chargingsystem may be damaged if the system fails or mal-functions due to excessive current or heat, voltagesurges, and other uncontrolled factors. Fusiblelinks are used in these circuits to protect the circuitform high current.

Common AC generators used by domestic man-ufacturers include the Delco-Remy SI and CS seriesused by OM; the Motorcraft IAR, rear-terminal, andside-terminal models used by Ford; and theDaimlerChrysler-built, Bosch, and Nippondensomodels used by DaimlerChrysler. Most Europeanimports use Bosch AC generators, while Asianimports use alternators made by several manu-facturers, including Hitachi, Nippondenso, andMitsubishi.

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Review Questions1. Alternators induce voltage by rotating:

a. A magnetic field inside a fixedconductor

b. A conductor inside a magnetic fieldc. A stator inside a fieldd. A spring past a stator

2. In an alternator, induced voltage is at itsmaximum value when the angle betweenthe magnetic lines and the loopedconductor is:a. 0 degreesb. 45 degreesc. 90 degreesd. 180 degrees

3. The sine wave voltage induced across oneconductor by one rotor revolution is called:a. Single-phase currentb. Open-circuit voltagec. Diode rectificationd. Half-phase current

4. Alternating current in an alternator isrectified by:a. Brushesb. Diodesc. Slip ringsd. Transistors

5. An alternator with only one conductor andone diode would show which of thefollowing current output patterns?a. Three-phase currentb. Open-circuit voltagec. Half-wave rectificationd. Full-wave rectification

6. An alternator consists of:a. A stator, a rotor, sliprings, brushes,

and diodesb. A stator, an armature, sliprings, brushes,

and diodesc. A stator, a rotor, a commutator, brushes,

and diodesd. A stator, a rotor, a field relay, brushes,

and diodes

7. A typical automotive alternator has howmany poles?a. 2 to 4b. 6 to 8c. 8 to 14d. 12 to 20

8. The three alternator conductors are woundonto a cylindrical, laminated metal-piececalled:a. Rotor coreb. Stator corec. Armature cored. Field core

9. Automotive alternators that have threeconductors generally use how many diodesto rectify the output current?a. Threeb. Sixc. Nined. Twelve

10. Which of the following is not true of thepositive diodes in an alternator?a. They are connected to the insulated

terminal of the battery.b. They conduct only the current

moving from ground into the conductor.

c. They are mounted in a heat sink.d. The bias of the diodes prevents the

battery from discharging.

11. A group of three or more like diodes may becalled:a. Diode wingb. Diode tripletc. Diode dishd. Diode bridge

12. Y-type stators are used in alternators thatrequire:a. Low voltage output at high alternator

speedb. High voltage output at low alternator

speedc. Low voltage at low alternator speedd. High voltage at high alternator speed

13. Which of the following is true of a delta-typestator?a. There is no neutral junction.b. There is no ground connection.c. The windings always form a series circuit.d. The circuit diagram looks like a

parallelogram.

14. Delta-type stators are used:a. When high-voltage output is neededb. When low-voltage output is needed

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c. When high-current output is neededd. When low-current output is needed

15. Which of the following is a commonly usedtype of field circuit in automotivealternators?a. X-circuitb. Y-circuitc. Connected-field circuitc. A-circuit

16. Alternator output voltage is directly related to:a. Field strengthb. Rotor speedc. Both field strength and rotor speedd. Neither field strength nor rotor speed

17. Double-contact voltage regulators containall of the following except:a. An armatureb. An electromagnetc. Two sets of contact pointsd. A solenoid

18. The shorting contacts of a double-contactregulator:a. Increase voltage creepb. Increase field currentc. React to battery temperature changesd. Short the field circuit to the alternator

19. Which of the following can not be used in atotally solid-state regulator?a. Zener diodesb. Thermistorsc. Capacitorsd. Circuit breakers

20. Which of the following is used to smooth outany abrupt voltage surges and protect aregulator?a. Transistorb. Capacitorc. Thermistord. Relays

21. Which of the following is used to monitor thecharging system?a. Ammeterb. Ohmmeterc. Dynamometerd. Fusible link

22. Warning lamps are installed sothat they will not light when the following is true:a. The voltage on the battery side of the

lamp is higher.b. Field current is flowing from the battery

to the alternator.c. The voltage on both sides of the lamp

is equal.d. The voltage on the resistor side of the

lamp is higher.

23. Maximum current output in an alternator isreached when the following is true:a. It reaches maximum designed speed.b. Electrical demands from the system are

at the minimum.c. Induced countervoltage becomes great

enough to stop current increase.d. Induced countervoltage drops low

enough to stop voltage increase.

24. The regulator is a charging systemdevice that controls circuit openingand closing:a. Ignition-to-batteryb. Alternator-to-thermistorc. Battery-to-accessoryd. Voltage source-to-battery

25. Which of the following methods is usedto regulate supply current to thealternator field?a. Fault codesb. Charge indicator lampc. Pulse-width modulationd. Shunt resistor

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