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How Alternators Work by Josh BriggsThis article How Alternators Work is from www.howstuffworks.com

It's 11: ! ".m. an# you $ust finishe# working a #ouble shift. It's late% you're tire# an# youha&e class in the morning. As you fumble for your car keys% you can't hel" but shi&er. It'sabout to snow .

ou ho" in your Hon#a (i&ic an# crank it u". The engine turns o&er gru#gingly bute&entually catches an# fires. After warming u" the engine% you "ull out an# begin yourhalf)hour $ourney home. Just as the heater begins to remo&e the frosty con#itions insi#ethe car% thera#io begins to cut out. *oon after% the #ash light starts to #im e&er so slightly.

ou kee" #ri&ing but theanomalies with your e&er)reliable car "ile u".

This is what it could come

to if your alternator dies without warning, and your

cell phone has no juice.

+&entually% the ra#io an#the heater ,uit altogether%an# the comfortable

warmth is slowly re"lace# by the outsi#e chill. our hea#lights are the ne-t thing to start going. ow you're gettingworrie#. /nly 1! more minutes an# you're home.

Those ne-t 1! minutes ne&er come. The hea#lights #im to the "oint of #angerous% an# theunthinkable ha""ens: The engine starts to miss. 0ess than 2ilometres from home% yourengine #ies% along with e&erything else in the car. ou coast to a sto" on the si#e of theroa# an# "ull out your cell "hone . It's #ea#% so you "lug it into the cigarette lighter so youcan call for hel". 3uess what4 o "ower. It's "ast mi#night% an# you're stran#e# on thesi#e of the roa# with snowflakes for com"any.

What you'&e $ust e-"erience# is an e-am"le of an alternator breathing its last breath.our first thought might ha&e been the battery is #ying. In a sense% you woul# be right because the battery an# the alternator are relate#% but the battery ten#s to get all the "ress.This article aims to e-"lain the mechanics of alternators% how you can #iagnose "roblemsan# what you can #o if you ha&e a ba# alternator. 5ea# the ne-t section to learn some

backgroun# information about alternators an# the war of the currents.

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What Is an Alternator?An automoti&e charging system is ma#e u" of three ma$or com"onents: the battery% the&oltage regulator an# an alternator. The alternator works with the battery to generate

"ower for the electrical com"onents of a &ehicle% like the interior an# e-terior lights% an#the instrument "anel. An alternator gets its name from the term alternating current 6A(7.

Alternators are ty"ically foun# near the front of the engine an# are #ri&en by thecrankshaft % which con&erts the "istons' u")an#)#own mo&ement into circular mo&ement.6To learn more about the basic "arts of car engines% rea# How (ar +ngines Work .7 *omeearly mo#el &ehicles use# a se"arate #ri&e belt from the crankshaft "ulley to thealternator "ulley% but most cars to#ay ha&e a ser"entine belt% or one belt that #ri&es allcom"onents that rely on crankshaft "ower. 8ost alternators are mounte# using bracketsthat bolt to a s"ecific "oint on the engine. /ne of the brackets is usually a fi-e# "oint%while the other isa#$ustable to tighten the#ri&e belt.

You can spot thealternator (with the tag

hanging off it) in theforeground of this shot ofa stoc car engine. You

can also see theserpentine !elt looped

around it.

Alternators "ro#uce A(

"ower throughelectromagnetism forme#through the stator an# rotor relationshi" that we'll touch on later in the article. Theelectricity is channele# into the battery% "ro&i#ing &oltage to run the &arious electricalsystems. Before we learn more about the mechanics of the alternator an# how it generateselectricity % let's look at the &arious "arts of an alternator in the ne-t section.

Alternator "omponents9or the most "art% alternators are relati&ely small an# lightweight. 5oughly the si e of acoconut% the alternators foun# in most "assenger cars an# light trucks are constructe#using an aluminum outer housing% as the lightweight metal #oes not magneti e. This is

im"ortant since aluminum #issi"ates the tremen#ous heat generate# by "ro#ucing theelectrical "ower an# since the rotor assembly "ro#uces a magnetic fiel#.

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Tesla: Scientist, Rock Band or Sports Car?

Time & Life Pictures/ Getty ma!es " picture of t#e !reat man

#i ola Tesla pa$ed the way to modern electricity, yetThomas %dison is re$ered as one of the greatest in$entorsof all time. Tesla and %dison were fierce ri$als who faced offin the war of the currents in the late &' s. While %dison iscredited with in$enting the first light !ul! and had the powermar et cornered with his wor on direct current or "

power, it was Tesla who de$eloped the first A" inductionmotor and A" power. After *eorge Westinghouse financially!ac ed Tesla, the two sides joc eyed for position in theelectricity mar et. %dison launched a propaganda assaultagainst A" power, going so far as de$eloping the electricchair to demonstrate the lethality of A" power. In the end,A" power won out, as it could tra$el much farther, producemore $oltage and ser$e more customers more efficiently.Tesla+s in$ention and pioneering wor pro$ided thefoundation for the modern alternator.

If you closely ins"ect an alternator% you'll fin# it has &ents on both the front an# backsi#e. Again% this ai#s in heat #issi"ation. A #ri&e "ulley is attache# to the rotor shaft onthe front of the alternator. When the engine is running% the crankshaft turns the #ri&e belt%which in turn s"ins the "ulley on the rotor shaft. In essence% the alternator transfers themechanical energy from the engine into electrical "ower for the car's accessories.

/n the back si#e of the alternator you'll fin# se&eral terminals 6or connecting "oints in anelectrical circuit 7. 0et's take a look at those:

S terminal ) *enses battery &oltage

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IG terminal ) Ignition switch that turns the &oltage regulator on

L terminal ) (loses the circuit to the warning lam"

B terminal ) 8ain alternator out"ut terminal 6connecte# to the battery7

F terminal ) 9ull)fiel# by"ass for regulator

(ooling is essential to an alternator's efficiency. It's easy to s"ot an ol#er unit by thee-ternal fan bla#es foun# on the rotor shaft behin# the "ulley. 8o#ern alternators ha&ecooling fans insi#e thealuminum housing. Thesefans o"erate the same way%using mechanical "owerfrom the s"inning rotorshaft.

This diagram shows thediodes, rotor assem!ly and

stator, all of which you wouldn+t normally see

without opening thealternator.

As we start to #isassemblethe alternator% we fin# the

#io#e rectifier 6or rectifier bri#ge7% the &oltageregulator% sli" rings an#

brushes. The regulator#istributes the "ower thealternator creates% an# it controls the out"ut of "ower to the battery. The rectifier bri#gecon&erts the "ower% as we'll learn in the ne-t section% while the brushes an# sli" ringshel" con#uct current to the rotor fiel# win#ing% or wire fiel#. ow let's crack the coconuto"en.

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/"ening the alternator re&eals a large cylin#er with triangular finger "oles aroun# thecircumference. This is therotor. A basic alternator isma#e u" of a series ofalternating finger "ole "ieces

"lace# aroun# coil wirescalle# fiel# win#ings thatwra" aroun# an iron core onthe rotor shaft. *ince weknow the "ulley attaches tothe shaft% we can now&isuali e how the rotor s"insinsi#e the stator. The rotorassembly fits insi#e the statorwith enough room ortolerance between the two% so

the rotor can s"in at highs"ee#s without striking thestator wall. /n each en# ofthe shaft sits a brush an# asli" ring.

This is what you might see if you were to open your alternator.

As we touche# on briefly% alternators generate "ower through magnetism. The triangularfinger "oles fi-e# aroun# the circumference of the rotor are staggere#% so the north an#south "oles alternate as they surroun# the wire rotor fiel# win#ings. This alternating

"attern creates the magnetic fiel# that in turn in#uces &oltage into the stator. Think of thestator as the catcher's glo&e as it harnesses all the "ower create# by the s"inning rotor.

All these com"onents work together to gi&e us the "ower we nee# to run our &ehicles.Tesla ca"ture# this electrical energy an# use# it to light u" cities% but we only nee#enough &olts to "ower our stereo% lights%win#ows an# locks . 0et's take a look at how thealternator "ro#uces that "ower in the ne-t section.

nderstanding Alternator -ower utput

In the early #ays% cars use# generators rather than alternators to "ower the &ehicle'selectrical system an# charge the battery. That's not the case anymore. As automoti&etechnology e&ol&e#% so #i# the nee# for more "ower. 3enerators "ro#uce #irect current%which tra&els in one #irection% as o""ose# to the alternating current for the electricity inour houses% which "erio#ically re&erses #irections. As Tesla "ro&e# in 1 ;% alternatingcurrent became more attracti&e as it generates higher &oltage more efficiently% somethingnecessary in contem"orary automobiles. But car batteries can't use A( "ower since they

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"ro#uce <( "ower. As a result% the alternator's "ower out"ut is fe# through #io#es % whichcon&ert the A( "ower to <( "ower.

A"/ " 0oc s 1ore than "urrentsThe hea&y)hitting rock ban# A(=<( forme# in Australia in 1>;?. 0egen# has it the

foun#ing members got their name after rea#ing the term off the back of an a""liance. The ban# "laye# u" to its name% with lea# guitarist Angus oung an# lea# singers Bon *cottan# then Brian Johnson gi&ing the ban# its #istincti&e high)&oltage soun#. The grou" sawma$or success in the 1> @s an# is still going strong% more than ?@ years after itsformation.

The rotor an# the stator are the two com"onents that generate "ower. As the enginerotates the alternator "ulley% the rotor s"ins "ast three stationary stator win#ings% or wirecoils% surroun#ing a fi-e# iron core that makes u" the stator. This is referre# to as a three)

"hase current. The coil win#ings are e&enly s"ace# at inter&als of 1 @ #egrees aroun# theiron shaft. The alternating magnetic fiel# from the rotor "ro#uces a subse,uent

alternating current in the stator. This A( current is fe# through stator lea#s into aconnecting set of #io#es. Two #io#es connect to each stator lea# to regulate the current.The #io#es are use# to essentially block an# #irect the current. *ince batteries nee# <(current% the #io#es become a one)way &al&e that will only allow current to "ass in thesame #irection.

Three)"hase alternators ha&e three sets of win#ings they're more efficient than a single) "hase alternator% which "ro#uce a single)"hase A( current. When working "ro"erly% thethree win#ings "ro#uce three currents that make u" the three "hases. A##ing all threetogether "ro#uces the total A( out"ut of the stator.

The two basic stator win#ing #esigns are #elta woun# an# wye style. <elta woun# areeasily i#entifiable by their sha"e% as they're triangular. These win#ings allow for a highcurrent flow at lower 5C8. Wye win#ings resemble the flu- ca"acitor seen in DBack tothe 9uture.D These win#ings are i#eal for #iesel engines% as they "ro#uce higher &oltagethan #elta stators at e&en lower 5C8.

After the A(=<( con&ersion% the resulting &oltage is rea#y to use in the battery. Toomuch or too little &oltage can #amage the battery% as well as other electrical com"onents.To ensure the correct amount% a &oltage regulator #etermines when an# how much&oltage is nee#e# in the battery. /ne of two ty"es of regulators are foun# in mostalternators: The groun#e# regulator works by controlling the amount of negati&e or

battery groun# going into the win#ing in the rotor% while a groun#e# fiel# ty"e works theother way aroun# ) by controlling the amount of battery "ositi&e. either "oses ana#&antage o&er the other.

With so many com"onents working to create the electricity &ital for our &ehicles% it's safeto say the alternator is a crucial com"onent un#er the hoo#. But like many "arts on ourcars% they fail. The ne-t section will gi&e you an i#ea of how to #etermine if you areabout to be stran#e# an# what you can #o if you nee# to re"lace your alternator.

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The 2ife and eath of an AlternatorAs we saw in the beginning of the article% a failing alternator will kill a battery an# ruinyour #ay. But why #i# the alternator fail in the first "lace4 Alternators ha&e mo&ing "arts%get #irty an# are sub$ect to stress from heat an# col#. As a result% the internal "artsgra#ually wear out.

/ne of the most common failures is bearing failure. The nee#le bearings that allow therotor to s"in freely insi#e the stator can break #own from #irt an# heat. When the

bearings fail% the rotor will not s"in efficiently an# can e&entually sei e. Esually analternator with bearings failure makes a lou# grin#ing noise. If you sus"ect this "roblem%it's only a matter of time before the alternator gi&es u". /l#er &ehicles with generatorsten# to re,uire much more maintenance than newer mo#els% but there's no har# an# fastrule for how long an alternator will last. It &aries from manufacturer to manufacturer.

ou can take se&eral easy ste"s to #iagnose whether your alternator is on the frit . 9irst%most cars to#ay ha&e a #ashboar# light that glows when the ignition is switche# on. This

light usually is re"resente# with a symbol of a battery. Ha&e you e&er hear# a bu ingnoise when the key is on% but the car isn't running4 That's the &oltage from the batteryrunning through the charging system. If this bulb is burne# out% chances are the alternatorwon't work. The car may start% but as we learne#% it's $ust a matter of time before the

battery #rains an# the electrical system fails.

As a rule% a three)"hase alternator can o"erate with only one of the stator win#ingso"erational% although it's only one)thir# as efficient. To test whether your car ha# an issuewith one of its stator win#ings% you'# nee# to use a &oltmeter to check the &oltage. 6 oucan buy a basic &oltmeter at an electronics store.7 This is calle# a loa# test. *ince the

battery "ro#uces <( "ower% set the &oltmeter to <( rather than A(. (onnect the re# lea#

6or wire7 to the "ositi&e terminal an# the black to the negati&e. With no accessories on%start the car an# raise the 5C8 to aroun# 1%@@@. The &oltage shoul# register aroun# 1&olts. Anything less than 1 may in#icate a "roblem. e-t% turn on the hea#lights% aircon#itioner% ra#io an# anything else that #raws electrical "ower. 5e& the engine an#check the &oltmeter. Again% the &oltage shoul# register aroun# 1 &olts. If you ha&e afailing alternator% the &oltage will be well below 1 &olts. If so% it's time to re"lace thealternator.

Before you #eci#e you nee# to yank the alternator an# re"lace it% make sure you checkthe ser"entine belt. If the belt is worn or loose% the alternator won't function "ro"erly. A

ba# belt is easy to re"lace an# won't set you back much% usually less than F @. But if you

ha&e to re"lace the alternator% you ha&e o"tions. 5ea# on to learn how to go aboutre"lacing an alternator an# what it may cost in the ne-t section.

Alternator 0eplacement9or the most "art% alternators are less e-"ensi&e than say% a "ower steering "um" or aircon#itioner com"ressor. e&ertheless% you ha&e alternati&es to forking out a lot of cashfor a re"lacement alternator. 8any automoti&e stores sell remanufacture# or rebuiltalternators at a #iscounte# "rice.

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*ometimes alternators are easily accessible an# sim"leto re"lace for the amateur mechanic. With a mo#estamount of automoti&e e-"erience an# the "ro"er tools%re"lacing an alternator in your garage can be #one. Butmore an# more cars #on't ha&e room un#er the hoo#%an# the alternators can be #ifficult to reach without firstremo&ing se&eral other com"onents. In this case% it's

best to take your car to an e-"erience# technician whocan #o the $ob ,uickly.

If you ha""en to own an alternator that has a re"air kita&ailable for sale% you can really sa&e some money.Alternator re"air kits run between F1 an# F?@%#e"en#ing on which com"onents you nee# to fi-. Again%you nee# the "ro"er tools an# a little know)how% but if

you're able to fin# the right kit an# know what you're #oing% you can rebuil# an alternatorfor a fraction of the cost of e&en a remanufacture# unit.

/ne thing is certain: A ba# alternator will ruin a goo# battery if you #on't a##ress it,uickly. Batteries can only be recharge# so many times before they'll lose their ability tohol# a charge. 9or the most "art% if the battery isn't relati&ely ol#% it shoul# sur&i&e. Butan ol#er battery that is constantly #raine# an# charge#% #raine# an# charge# will ha&e ashorter life s"an than a battery o"erate# un#er normal con#itions. The a&erage life s"anof a battery is usually aroun# months.

Alternator 3uestions1. What is an alternator an# why is it im"ortant to your car4

. Who was Tesla an# why was he im"ortant4?. What are the terminals on the back of the alternator for an# what #o they #o4

. ame the "arts of the alternator an# state what they #o.!. Why is it #esirable to con&ert "ower from <( to A(4