This document summarizes the principal electric circuits used in motor vehicles, including the starting circuit, ignition circuit, lighting circuit, charging circuit, and other auxiliary circuits. It provides details on how each circuit works, including components like the battery, distributor, spark plugs, and switches. The circuits power essential functions like starting the engine, providing ignition, and lighting the headlights, taillights, and other lamps.

1. AUTOMOBILE
ELECTRIC CIRCUIT

2. Theprincipalcircuitsusedinmotorvehiclesareasfollows
1. Startingcircuit
2. Ignitioncircuit
3. Lightingcircuit
4. Chargingcircuit
5. Instrumentcircuit
a. Electricpetrolgaugecircuit
b. Wipercircuit
c. Horncircuit
d. Sideindicator
e. Fan,radio,taperecordercircuit.

3. Onlypositivewireisrunforallthe abovecircuitfromthebattery,whilenegativeis
earthedtothevehiclechassis.Thechassisisalsoknownasearthline.Negative
pointsofallthecircuitsareconnectedtothechassisorearthline.
StartingCircuit:-
Theoldtypeofengineswerestartedbyahandle,whichwasrotatedmanytimesby
hand.Sometimes,theworkusedtotakealotoftimeandlabour.Therotationofthe
handleusedtoproduceasparkinthemixtureofpetrolandair,andasaresultpetrol
gaswasformedinthecylinderwhichoperatedthepiston.But,nowadaysthedriver
hastopushabuttontostarttheengineanditdoesnotrequireanylabourortime.

4. Ad.c.seriesmotorisusedforthepurposebecauseitgivesmorestartingtorque.Of
course,themotordrawsaheavycurrentinthestartfromthebatterywhichcanbeof
theorderof200amperes.Thefieldofad.c.seriesmotorismadeof afewturnsof
thickcopperwire,anditisconnectedinserieswiththearmature.The d.c.supplyis
suppliedtothearmaturethroughthebrushesandthecommuter.Themotormust
notbeoperatedwithoutloadbecauseinsuchcondition,itwillrunataterriblespeed
anditwillbeabletobreak.Therefore,asystemofgearsisarrangedinsuchaway
thatonstartingthemotor,theenginewillstart.As theengineisstarted,themotoris
switchedoffanditsgearsystemgetsseparatedfromthatoftheengine.Thestarting
switchmaybeafootpedalswitchwhichstartsthemotorinfirstpushandstopsthe
motorinthesecondpush,oritmaybekeyoperatedswitch.
Thefollowingtwomethodsareusedforstartingtheengine.
1. Pedomaxsystem
2. Bendixdrivestarterswitchsystem

5. LightingCircuits
Amotorvehiclehasthefollowingtypesoflightingcircuits:
1. Headlamp
2. Sidelamp
3. Taillamp
4. Panelboardlamp
5. Stoplamp
6. Doorlamp
7. Internallamp
8. Parklamp

6. 1.HeadLamp– Amotorvehiclehastwofrontheadlampseachhavingadouble
Filament.Oncefilamentisof30wattsandtheotherof5watts.Thereflectorofthe
lampiscapabletoradiatethelightraysuptoadistanceof200–300meters.
Boththelampsareconnectedtothedimmeranddipperswitch;whichisasortof
two-wayswitch.Inonepositionitcompletesthecircuitof5wattfilamentswhile in
theotherthatof30wattfilaments.Asshown.

7. 2.SideLamp– These aretwosmalllampsplacednearheadlampsontheir
outwardsides.Thelampsareswitchedonduringnightjourneysoastoindicatethe
widthofthevehicle.Theyareof3to6wattshavingasinglefilament.

8. 3.TailLamp – Thislampisplacedjustabovethenumberplateofthevehicle’s
back.Itiscoveredwitharedcolouredshade.Itisconnectedinserieswiththepanel
lamsothatthedrivermayrestassurethatthe taillampofhisvehicleisglowing.
Thislampindicatesthepresenceofavehicleontheroadtotheothervehicles
followingit;alsoitenlightsthebacknumberplateofthevehicle

9. 4.PannelBoardLamp–Itis3wattlampwhichisconnectedinserieswiththe
Taillamp.Itenlightsthepannelboardwhichhousesmanytypesofswitchesand
meters.

10. 5.StopLamp-Thislampisplacedontheothersideofthetaillamponthe
vehicle’sback.Itisalsomountedwitharedcolouredshade,anditisa3wattlamp.
Itisattachedtothebrakesystem.Whenthebrakesareapplied,thestoplampis
alsoswitchedtoOFF.Itglowsonreducingthespeedorstoppingthevehicleoron
turns.

11. 6.DoorLamp -Thedoorlampismountedonthepannelboardbutits
switchesaremountedoneachdoorofthevehicle.Alltheswitchesareconnectedin
parallelwhereasachswitchisooppositetypei.e.onpressingtheswitchthecircuitI
switchedoff.Now,Ianyoneofthedoorsisopen,thenthedoorlampwillglowand
itsglowwillindicatethatanydoorisleftopen.
Whenallthedoorsofthevehiclesareclosedthenonlythelampwillgetoff.

12. 7.InternalLamp-Thelampsplacedinsidethevehiclearecalledinternal
lamps.Theyareof6watts.Theirswitchesaremountedonthepannelboard.6watts
lampsareusedfordimlightingand20wattslampsareusedforbrightlighting

13. 8.ParkLamp-Four 3wattslampsaremountedonthevehiclewhichareput
toONwhileparking.Twolampsaremountedinthefrontsidenearsidelampsand
theresttwointherearsidenearstoplamps.

14. IgnitionCircuit:-
Generally,allmotorvehiclesemploybatteryfortheirignitionsystem.Ignitionmeans
firinginthemixtureofpetrolandair.Theignitionisproducedthroughspark-plugs,
anditcausesanexplosioninthepetrol-airmixturewhichgeneratesmechanical
powertooperatetheengine.12or24voltsbatteriesareusedinmotorvehiclesfor
ignitionandotheruses.

15. Thesystemconsistsofthefollowingparts:
1. Battery
2. Ignitionoil
3. Distributor
4. Ignitionswitch
5. Sparkplug

16. ScreenWiper:-
Electricoperatedscreenwipersareusedinmotorvehiclesforthecleaningofglass
screenfittedinfrontofthedriver’sseat.Itconsistsofad.c.motorandagear-box,
asshown.Thed.c.motorisofshuntorcompoundwoundtype.Thegearmounted
onthemotorshaftreducesthemotorspeed.Therearesomemoregearsconnected
totheshaft-gearwhichoperatesthewipertoandfro.Thewoolenclothbrush
mountedonthewipercleanstheglass.Onemorewipermayalsobecoupled
mechanicallytothemainwipersoastocleantheglassoftheothersidealso.

17. ElectricHorn:-
Electricoperatedhornsareusedforproducingaloadsoundasandwhenrequired.
Theyareoffollowingtwotypes:
1. Magnettypehorn
2. Motortypehorn

18. 1.MagnetTypeHorn – Itconsistsofanelectromagnet,movingarmature,
diaphragm,C.B.pointsandanadjustingscrew.Theassemblyofthehornisshown.
Onpushingthehornswitch,thecurrentwillflowthroughtheelectromagnet’scoil
andwillmagnetizeit.ThearmatureattractstheC.B.pointsleafandthusbreakthe
circuit.Theelectromagnetwillthengetdemagnetizedandthearmaturewillreturnto
itsoriginalposition,therebyshortcircuitingtheC.B.
pointsonceagain.Thus,thecircuitwillmakeandbreakatafrequencyof75
to125H,andwillcausethediaphragmtovibratewhichwillproducesound.

19. 2.MotorTypeHorn - Thistypeofhornconsistsofa6or12voltsd.c.motor
Whoseoneterminalisearthedandtheotherisconnectedtothebatterythroughthe
motorfieldandthecommutator.Atoothedwheelismountedonthemotorshaft.
Anotherfixedtoothedwheelismountednearthefirstoneanditisattachedto
diaphragm,asshown.
Onpushingthehornswitch,themotorisstartedandthetoothedwheelmountedon
themotorshaftwillrotate,anditsteethwillstriketheteethofthefixedtoothed
wheel.Thus,thediaphragmwillvibrateandwillproducesound.Theintensityofthe
soundproducedcanbevariedinaccordancewiththemotorspeed.

20. SideIndicator
Twosideindicatorlampsoneoneachsideofthevehicleareusedtoindicatethe
directionoftamingofthevehicle.Theyarecontrolledbyathreewayswitch.The
polepointoftheswitchisconnectedtothebatteryandthetwothrowpointsare
connectedtotheleftandrightside-lamps,whilethethirdthrowpointisleftforOFF.
Thecircuitconnectionsareshown.
Sometimes,ironarrowindicatorsarealsousedinassociationwiththesidelamps.
Theyareoperatedbyelectromagnetsandtheircircuitconnectionsareshown.