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					ELECTRICALS


Prof . Siddiqui Aqleem
    Electrical System Requirements

• Power Plant under the hood of Automobile

• Supply power for ignition, lights and other electrical
  accessories

• Produces and stores electrical energy, which is at low
  voltage or high voltage surges

•Electrical systems required to function for a long period of
 time without failure

• Made to operate under wide variation of operating
  conditions
    Automobile Electrical System
           Categories


1.Generation, Storage and Distribution
2.Starting System
3.Ignition System
4.Lighting System
5.Accessories
   Automobile Electrical System
Generation, Storage and Distribution

   • Generator
     •AC Generator
     •DC Generator
   •Battery
   •Regulator
Automobile Electrical System
       Starting System



• STARTER MOTOR
Automobile Electrical System
       Ignition System



• CONVENTIONAL
• ELECTRONIC
• COMPUTER CONTROLLED
Automobile Electrical System
         Lighting System



•Lamps
  •Head lamps
  •Tail lamps
• Indicators
•Lights for illumination
Automobile Electrical System
          Accesories



•Horn
•Wipers
•Radio
•Heater
•Speedo/Tacho meter
Automobile Electrical System
       LEAD – ACID BATTERY



• It is an Electro-Chemical device
• Supplies current due to chemical action
• Major components :
   • Container
   • Plates
   • Seperators
   • Cell Covers
   • Electrolyte
Automobile Electrical System
   LEAD – ACID BATTERY
Automobile Electrical System
   LEAD – ACID BATTERY
       Automobile Electrical System
                LEAD – ACID BATTERY
Container




            •   Single piece construction
            •   Made of hard rubber or bituminous material
            •   Modern covers made of polypropylene
            •   Partitions are made to divide into
                compartments for cells
            •   Ribs provided at the bottom
Automobile Electrical System
                                                         Platess
      LEAD – ACID BATTERY




 •   Positive & Negative Plates
 •   Grid of alloy of lead and antimony
 •   Grid gives strength to lead
 •   More antimony , more gases, hence more water to be added
     periodically
 •   Maintenance free battery has grid of % calcium instead of
     antimony. Hence do not require water during normal use
 •   Active materials are :
      • Positive plate -- Lead Peroxide (PbO2)
      • Negative Plate -- Spongy Lead (Pb)
Automobile Electrical System
                                                               Seperators
         LEAD – ACID BATTERY




•   To avoid direct contact and hence short circuiting
•   Made of wood, ebonite, porous rubber, fibre glass, resin
    bonded cellulose and sintered PVC
Automobile Electrical System
    LEAD – ACID BATTERY
               Plate Groups




•All like plates are connected by lead
strap, soldered to a lead lug
•One negative plate more than positive
plate
Automobile Electrical System
   LEAD – ACID BATTERY
           Plate Groups
Automobile Electrical System
   LEAD – ACID BATTERY
           Electrolyte
Automobile Electrical System
   LEAD – ACID BATTERY
           Chemical Action
 Automobile Electrical System
          LEAD – ACID BATTERY
                 Chemical Action




Positive Plate   Electrolyte       Negative Plate
Automobile Electrical Systems                   LEAD – ACID BATTERY
                                                         Battery Ratings


                                •Measure of energy stored in it
                                •Capacity of battery depends on :
                                    • Number of plates per cell
                                    • Thickness and size of plates
                                    • Cell size
                                    • Quantity of Electrolyte


                                Most commonly used battery ratings are :
                                • 20-h Rate
                                • 25-A Rate
                                • Cold Rate
                                • 4-h Rate
Automobile Electrical Systems                      LEAD – ACID BATTERY
                                                             Battery Ratings

                                               20-H Rate ( Ampere Hour Capacity)



                                • Represents the rate of current a battery can deliver continuously for 20
                                hours till cell voltage drops to 1.75V


                                •Indicates the lasting power of battery


                                •A 6V battery rated as 100AH, will deliver 1/20 of 100 i.e. 5A for 20H till
                                terminal voltage falls to 5.25V
Automobile Electrical Systems                     LEAD – ACID BATTERY
                                                            Battery Ratings




                                              25-A Rate ( Ampere Hour Capacity)



                                • It is the measure of the battery performance at moderate constant-
                                current output till cell voltage drops to 1.75V
                                • It indicates the ability of the battery to carry the electric operating load
                                of an automobile when the generator is not functioning
Automobile Electrical Systems                    LEAD – ACID BATTERY
                                                          Battery Ratings




                                                            Cold Rate



                                • Also termed as short time rate
                                •Indicates the current which battery can supply continuously for 30
                                seconds without cell voltage dropping to 1.0V, at temp of -180C
                                • Indicates the ability of the battery during cold weather starting
Automobile Electrical Systems                    LEAD – ACID BATTERY
                                                         Battery Ratings




                                                             4-h Rate



                                • This rating is used for heavy vehicles
                                • Represents the ampere-hour rating of a battery discharged in 4-h
                                • A battery supplying 25A for 4h will have 100Ah on the 4-h rate
Automobile Electrical Systems                     LEAD – ACID BATTERY

                                                     State of Charge of Battery




                                1.28 Fully Charged             2.00 Fully Charged


                                1.14 Discharged                1.70 Discharged


                                1.11 Fully discharged          1.50 Fully discharged
Automobile Electrical Systems          LEAD – ACID BATTERY
                                               Battery Failures




                                • Overcharging

                                • Cycling

                                • Sulphation

                                • Internal Short Circuit

                                • Self Discharge
Automobile Electrical Systems                  LEAD – ACID BATTERY
                                                      Battery Failures

                                                        Overcharging




                                • Occurs due to prolonged charging

                                • Excessive heat is produced

                                • Swelling of positive plates due to free oxygen reacting
                                  with it

                                • Seperators become brittle and start to crumble
Automobile Electrical Systems                      LEAD – ACID BATTERY
                                                           Battery Failures

                                                               Cycling




                                • Normal failure due to charging and discharging
                                • Active materials of –ve plate swell and contract
                                • Shedding of active materials takes place
                                • +ve plate active material become soft, muddy and
                                brown in color and falls due to gassing
                                • Active materials falling at the bottom will produce
                                short circuit
Automobile Electrical Systems                     LEAD – ACID BATTERY
                                                         Battery Failures

                                                            Sulphation




                                • Battery when discharged has Lead Sulphate on +ve
                                and –ve plates
                                • If charged immediately, sulphates get converted
                                • If allowed to stand for long period, lead sulphate
                                becomes hard and will not resist reconversion
                                • -ve plates become greyish white colour
                                • +ve plates become milky white colour
                                • Plates tend to expand and break
Automobile Electrical Systems                    LEAD – ACID BATTERY
                                                        Battery Failures

                                                     Internal Short Circuits




                                • Results due to failure of seperator
                                • Results due to bridging of materials at the bottom
                                • Detected by orange coloured spots on plates
                                seperators
Automobile Electrical Systems                     LEAD – ACID BATTERY
                                                           Battery Charging




                                • DC supply is essential
                                • AC if available, should be rectified
                                • Requires greater amount of charging in low state of charge
                                •Regulation of current and voltage is required
                                • Different types of charging methods are :
                                    • Constant Current Charging
                                    • Constant Voltage Charging
                                    • Booster or High-rate Charging
Automobile Electrical Systems                      LEAD – ACID BATTERY
                                                          Battery Charging

                                                    Constant Current Charging


                                • Battery is charged at a constant current
                                • If batteries of different ratings are charged in series, then
                                charging rate decided by the battery with lowest rating
                                • Battery charging is continued till gassing occurs
                                • Charging is stopped when no further rise in specific gravity
                                of electrolyte takes place for another two hour
Automobile Electrical Systems                     LEAD – ACID BATTERY
                                                         Battery Charging

                                                    Constant Voltage Charging


                                • Works on the principle that when the battery nears its charge
                                state it’s terminal voltage increases
                                • A motor generator set is normally used for such type of
                                charging
                                • Generator gives 7.5V or 14.5V
                                • In low state of charge, high rate of charging current flows
                                • Near full charge state, increase in battery terminal voltage
                                will result in opposition to charging current
Automobile Electrical Systems                    LEAD – ACID BATTERY
                                                       Battery Charging

                                                  Booster/High Rate Charging


                                • Booster devices supplying high charging current (40-100A)
                                are employed
                                • Charging process is boosted up
                                   • Battery is recharged almost fully in one hour
                                • Precautions
                                   • Good condition of battery
                                   • Non sulphated
                                   • Electrolyte temp not to rise above 500C
Automobile Electrical Systems                    LEAD – ACID BATTERY
                                                        Battery Charging

                                                  Charging Sulphated Batteries




                                • Put on half charge rate for 60-100 hours to check if
                                sulphation is broken down
                                • Original life expectancy can never be restored

				
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posted:3/25/2011
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