Automobile engineering (Classification of batteries, battery construction, maintenance, testing and charging, cutout, lighting circuit, horn, indicators)

BATTERY 

Battery is an electrochemical device which converts chemical energy to electrical energy when 

discharging and electrical energy to chemical energy while charging. The main purposes of 

battery are to store electrical energy andto provide a supply of current for cranking the starting 

motor and for other electrical

 Different types of Battery 

1. Lead acid battery 

2. Alkaline battery 

3. Zinc - air battery 

4. Nickel - Metal hydride battery 

5. Lithium - ion battery 

LEAD ACID BATTERY 

CONSTRUCTION 

The major components of the battery are: 

1. Container 

2. Plates 

3. Separators 

4. Cell 

5. Electrolyte

Container

They are of single piece construction made of polypropylene which is very strong and light

weight plastic. There are partitions inside the container for different cells. To avoid the short of

positive and negative plates, bridges are formed at the bottom of the container.

Plates

There are two types of battery plates

1. Positive plate

2. Negative plate

For each plate there is supporting grid made of alloy of lead and antimony. The function of grid

is to hold the active material and to carry current in the plates.

The active material in the positive plate grid is lead peroxide (PbO2) in chocolate colour and

negative plate is spongy lead (Pb) in grey colour. These plates are immersed in dilute sulphuric

acid. There are separators to keep the positive and negative plates apart. These separators are

made of non - conducting porous materials and prevent short circuits.

A number of positive plates are lead burnt to a post strap to form a positive plate group; while

the negative plate group contains one plate more than positive group so that both side of positive

plates can be utilized as greater electro chemical activity takes place. The positive plate post is

usually larger in diameter than the negative plates.

Cells

One positive and one negative group of plates are slide over each other with separators in

between, to form cell. Each cell supplies a current of 2V. i.e, a12 volt battery consists of 6 cells.

The size of the plates and their number per cell determines the capacity of the battery. Cells are

connected in series.

Electrolyte

After assembling completely, the battery is filled with electrolyte. It is a solution of water and

sulphuric acid. It contains approximately one part of sulphuric acid and two parts of water by

volume. In fully charged condition, the gravity is 1.290 at 15 degree where; the specific gravity

of fully discharged battery is about 1.110.

Working of lead acid battery

Chemical equation of a battery while discharging and charging is given below:

PbO2+ 2H2SO4+ Pb ---------- discharging PbSO4 + 2H2O + PbSO4

--------- charging

(+ve plate electrolyte -ve plate) (+ve plate electrolyte -ve plate)

On discharging both PbO2 and Pb are converted to lead sulphate, (PbSO4) and water is

produced, which dilutes the electrolyte solution. During recharging, lead sulphate on positive

plates is converted into lead peroxide (PbO2), while on negative plates lead sulphate is converted

to spongy lead. Water is split up into oxygen and hydrogen gases during charging process. The

hydrogen combines with the sulphateions to reform sulphuric acid. In this way the specific

gravity of electrolyte is increased during the charging process.

CHARACTERISTICS OF BATTARY

CELL VOLTAGE

The open circuit voltage of a fully charged battery cell is 2.1V. A six volt battery would,

therefore, be made of 3 cells, while a 12 volt battery would contain 6 cells connected in series. It

may be noted that cell voltage is not affected by the cell sizeand the number of plates.

BATTERY CAPACITY

The capacity of a battery is defined as the amount of current it can deliver. It depends upon the

number and area of plates in the cell and the quality of the electrolyte. It also depends upon the

temperature of electrolyte.

BATTERY RATINGS

It is determined by the current it can produce and the time for which it can sustain this current.

Some types of ratings are:

1. 20 hour rate - it indicates the lasting power of battery on small load. That is the rate of current

a battery can deliver continuously for 20 hours after which the cell voltage should not drop

below 1.75 volts.

2. Reserve capacity - This is the length of time that a fully charged battery at 27 degree Celsius

can deliver 25 Amperes. A typical rating is 125 minutes in which a battery can be discharged at

25 amperes for 125 minutes if the alternator is not working.

BATTERY CHARGING

If the battery charge has got down to a lower value, the run of vehicle is not sufficient to charge

the battery. In this condition the battery is to be charged from other external sources. There are

different methods of battery charging. They are:

1. Slow Rate Charging

i) Constant voltage charging

ii) Constant current charging

2. Quick Rate Charging or Booster Charging

3. Trickle Charging

1. Slow rate charging

Ordinarily batteries are charged by slow rate charging method. It takes about 12 to 20 hours for

charging a battery using this method. It is the safest method of charging as it increases the life of

a battery. There are 2 types of slow rate charging. They are

i) Constant voltage charging

This type of charger is a motor generator set. The generator is rated 15 volts for 12 volt batteries.

When the battery in a discharged condition is connected to the generator, current will flow into

the battery. As the battery nears its charge, its terminal voltage will increase with increase in

opposition to charging current. Thatis the charging current tapers off as the battery approaches

the charged condition.The battery should be removed from the charger if the temperature

increases beyond the limit.

ii) Constant current charging

This type of charger is a rectifier. The charging current of this rectifier can be adjusted with the

help of a rheostat. The battery may be charged at 5A rate. The charging may be continued till all

the cells of the battery are gassing freely and no further rise in the specific gravity of the

electrolyte takes place for another 2 hours.

2. Quick Rate Charging or Booster Charging

Boosters are devices which supply high charging currents of 40 to 100A, depending upon the

size of the battery. It is possible to recharge a battery to almost the full charge condition in an

hour using this process. Some precautionsshould be taken before attempting booster charging.

They are:

1. The battery must be in good condition.

2. A badly overcharged battery which has been allowed to stand idle for long period should not

be charged this way.

3. A badly sulphated battery should not be quick charged.

4. The electrolyte temperature should not be allowed to rise above 500 C.

CARE AND MAINTENANCE OF BATTERY

The vehicle batteries must be inspected periodically, say, every week. The following points may

be taken care of.

1. The battery terminals should be clean and tight.

2. Remove vent plugs while charging.

3. Never bring flame near vent holes while charging as it may cause explosion.

4. In case the electrolyte level in the battery is not sufficient, top up with distilled water.

5. Never let the battery remain in discharged condition, otherwise the plates will become

sulphated.

6. Do not put weight on battery as it may bend the plates.

7. Do not hammer the battery terminals.

8. Put petroleum jelly on battery terminals to avoid sulphation.

9. To avoid accidental arching, always remove the negative cable first while disconnecting and

connecting the battery.

10. Avoid the contact of electrolyte with eyes, skin or cloths

Starting system

Starting system uses battery power and an electric DC motor to turn engine crankshaft for engine

starting. It changes electrical energy to mechanical energy. It provides gear reduction/torque

multiplication (16:1 to 20:1). When the ignition key is turned on the current flows through the

solenoid coil, this closes the contacts, connecting battery to the starter motor.

STARTING CIRCUIT

The starting system includes the battery, starter motor, solenoid, ignition switch and in some

cases, a starter relay. An inhibitor (neutral safety) switch is included in the starting system circuit

to prevent the vehicle from being started while in gear.

When the ignition key is turned to the start position, current flows and energizes the starter's

solenoid coil. The energized coil becomes an electromagnet which pulls the plunger into the coil;

the plunger closes a set of contacts which allow high current to reach the starter motor. On

models where the solenoid is mounted on the starter, the plunger also serves to push the starter

pinion to mesh with the teeth on the flywheel.

LIGHTING CIRCUIT

The purpose of the lighting system is to provide illumination for the driver to operate the vehicle

safely at night, to convey information to the other driver and people on the road about the

vehicle's presence, position, size, direction oftravel, illuminating instruments on the dash board

etc. The automobile lighting system consists of the following circuits:

1. Head lamp circuit 2. Tail lamp circuit

3. Stop light circuit 4. Parking light circuit

5. Number plate light circuit 6. Instrument panel light circuit

7. Interior light circuit

HEAD LAMP

A head lamp is a lamp attached to the front of a vehicle to light the road ahead with a reasonable

distance with sufficient intensity. For this purpose a reflector is used. The following are the

important types of head lamps.

1. Incandescent lamp

2. Halogen lamp

3. High intensity discharge (HID) lamp

4. LED lamp

LIGHTING SWITCHES

Switches used in lighting circuit of an automobile are of different types depending upon their

requirements. The important switches area) Light switch: - This may be of push-pull type and is mounted on the board.It has three

positions (i) off position, (ii) side lamps, tail lamps, number plate light and instrument lamps (iii)

head lights. This switch is also mounted on a stick on the steering column.

b) Dimmer switch: - This switch is mounted on the stick on the steering column.

By moving the lever up and down, we can select the dim and bright position of the head lamp.

c) Stop light switch: - This is attached to the master cylinder in the brake system. When the brake

pedal is applied, the fluid pressure developed in the compression chamber is communicated to a

metallic diaphragm which deflects to close the two terminals for the stop light switch.

Ok

These lights are used to indicate the driver about the position and situations of different systems.

a) Main beam warning light:-This light glows when the main beam of the head lights are on. This

reminds the driver to dip the lights for the oncoming vehicles.

b) Ignition warning light: - The red light lights up when the ignition switch is on. It goes off

when the engine speed increases. This lamp serves as a warning against leaving the ignition

switched on when the engine is not running.

DIRECTION INDICATOR CIRCUIT

One light on each side is fitted both at the front as well as on the rear side of the vehicle. The

wiring diagram for the same is shown in the figure. The current is taken from the battery through

a fuse and a flasher unit. The flashing indicator switch is usually in the form of a horizontal lever

mounted on the steering column so that when its outboard end is actuated upward, the light side

indicator lights are operated and the downwards movement of the switch arm operates the right

side indicator lights. Flasher unit consists of a thermostatic bimetallic blade. The blade expands

due to flowing of the current through it, warms and opens a pair of contacts, thus opening the circuit. But as the current stop flowing, the blade cools and straightens to close the circuit again.

In this way the lights are made to flash.

HORN CIRCUIT

The horn employed on present-day automobiles is electrically operated. 

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