Battery Used in Automobiles

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Battery used in

Automobiles


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INTRODUCTION

Main part of electrical system in an automobile.

Electrical system consists of 4 main circuits:

a) Generating circuitb) Starting circuit

c) Ignition circuit

d) Lighting circuit

These main circuits are connected togetherto the car battery( rechargeable).


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Without battery, engine cannot be started with starting

motor. Battery supplies current for operation of starting motor

and ignition system when engine is being cranked forstarting.

It also supplies current for light, radio, heater and severalother accessory units when generator is not operatingfast enough to handle the electrical load.

It can be used again once discharged with the help ofalternator of the car.

If a battery is left standing for few days, it will dischargedby itself. New batteries usually get discharged by itself at

the rate of 1% per day of storage. The rapid selfdischarge (3% or more) is considered a serious defect ofbattery.


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Types of batteries

Lead acid battery

Alkaline battery( nickel iron type or nickel

cadmium type)

Zinc air battery


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Battery Construction


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Battery consists of following components:

CONTAINER

1)It is single piece construction.

2)It is made up of hard rubber or plastic.

3)It should not absorb acid and withstand extreme heat and cold.

4)It is divided into compartments by partitions for different cells.Bridges are formed at the bottom of each compartment on whichbattery plate rest. The space between bridge ribs are provided to

collect sediments.T

his minimize danger of short circuit due tosediments.

5)Gasoline should be kept away from bituminous compositioncontainers as they will dissolve bituminous binders.


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PLATES:

1)In a battery, several similar plates are properly spacedand welded.

2) These plates consists of perforated grids into which

lead or lead peroxide has been pressed.

3) Grids are made of an alloy of lead and antimony which

make it resistant to electrochemical corrosion.

4) Plate groups are arranged in the cell so that positive

and negative plates alternate.

5) Positive plates are filled with lead peroxide active

material and negative plates are filled with a porousmass of lead in spongy form in which electrolyte can

penetrate freely.


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GRIDS:

1) The plates of battery consist of an electricallyconducting grid framework in the meshes of which

active materials are incorporated by electrochemical

process.

2) These grids serve to conduct current to and from the

active materials of positive and negative plates.

3) An alloy consisting essentially of lead and antimony is

used for grids.

4) Antimony strengthens the soft lead and fascilates

casting of fine detail of wire structure of grids andenables the battery weight to be kept minimum.


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SEPERATORS:

1) They are placed between negative and positive plates to keep

them separate between each other.

2) They are porous so that liquid can be circulated between plates.

3) They may be made of polyvinyl chloride or polyethylene saturated

cellulose.

CELL COVER:

1) Each cell is sealed by a cover of hard rubber through which the

positive and negative terminal project.

2) Each cover has opening through which liquid can be added.

3) Vent plugs of special designs co-operate with cover vent opening

to baffle gases and electrolyte is splashed and sprayed againstunderside of the cover to prevent loss of acid from the cell.


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ELECTROLYTE:

1) Electrolyte used in lead acid battery is the solution of sulphuric

acid which consists of 40% Sulphuric acid and 60% distilled

water.

2) The active materials of battery cannot become active until they

are covered with aqueous electrolyte solution.

CELL CONNECTOR:

1) To connect the cells of battery in series, the elements are placed

in each cell so that negative terminal of one cell will be adjacent to

positive terminal of next cell and so on throughout the battery.

2) Cell connectors are placed over protruding terminal parts and

welded to them to connect the cell in series.

TAPEREDTERMINALS:

Battery terminals are tapered to specified dimensions so that all

positive and negative cable clamp terminals will fit any

corresponding battery terminal interchangeably.


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Chemicals used in batteries

(Lead acid battery)

Spongy lead (solid) (held in plate grids)

Lead oxide (paste) (interlocking horizontal

and vertical bars of plate grid holds them

in the plate)

Sulphuric acid( liquid) (mixed with water incontainer)


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Zinc Air Battery Non-rechargeable batteries.

Electrochemical batteries powered by oxidizing zinc with oxygenfrom the air.

It is metal-air electrical storage and discharge device that worksthrough the oxidization of zinc.

The operating life of a zinc-air cell is a critical function of itsinteraction with its environment.

Reaction formulas: Anode: Zn + 4OH Zn[(OH)4]2 + 2e (E0 = 1.25 V)

Fluid: Zn[(OH)4]2 ZnO + H2O + 2OH

Cathode: O2 + 2H2O + 4e 4OH (E0 = 0.4 V)

Overall: 2Zn + O2 2ZnO (E0 = 1.65 V)

1.65 is theoretical value. It is reduced to 1.4-1.35 in available cell.

Zinc-air batteries have higher capacity-to-volume (and weight)ratio than other types of battery because air from theatmosphere is one of the battery reactants.


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Uses Large zinc-air batteries, with capacities up to 2,000

amperehours per cell, are used to power navigationinstruments and marker lights, oceanographicexperiments, and railway signals .

Very small button cell zinc-air batteries are used forhearing aid, larger batteries are used in film camerasthat previously used ,mercury batteries, very largebatteries are used for electric vehicle propulsion.

Zinc air batteries allows full size delivery vans toroutinely run 400 km. on a single charge. Once low, the

batteries are exchanged in less than 10 minutes andrecharged at a central plant.


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Why not rechargeable?

Rechargeable zinc-air cells are a difficult

design problem since zinc precipitation

from the water-based electrolyte must beclosely controlled.

The problems are dendrite formation, non-

uniform zinc dissolution and limitedsolubility in electrolytes.


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zinc-air fuel cells are mechanically rechargeable.1)Mechanical recharging systems have been researched for

decades for use in electric vehicles .

2)Rechargeable systems may mechanically replace the anode

and electrolyte, essentially operating as a refurbishable

primary cell, or may use zinc powder or other methods to

replenish the reactants.


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Alkaline batteries Alkaline batteries are a type of primary battery or rechargeable

battery dependent upon the reaction between zinc and manganesedioxide (Zn/Mno2).

They have a higher energy density with same voltage as compared

to zinc carbon batteries. It has an alkaline electrolyte of potassium hydroxide.

The anode (negative terminal) is made of zinc powder, which givesmore surface area for increased current, and the cathode (positiveterminal) is composed of manganese dioxide.

The half-reactions are: Zn (s) + 2OH (aq) ZnO (s) + H2O (l) + 2e 2MnO2 (s) + H2O (l) + 2e Mn2O3 (s) + 2OH (aq)


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Section through an alkaline battery


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Nickel iron alkaline battery

The nickel-iron battery (NiFe battery) is a storagebattery having a nickel(III) oxide-hydroxide cathode andan iron anode, with an electrolyte of potassium

hydroxide. The open-circuit voltage is 1.4 volts, dropping to 1.2 volts

during discharge.

The half-cell reaction at the cathode: 2 NiOH + 2 H2O + 2 e 2 Ni(OH)2 + 2 OH

and at the anode: Fe + 2 OH Fe(OH)2 + 2 e

Discharging is read from left to right.


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Specific gravity( at 300K) of

electrolyte

1.220-1.230 when electrolyte is fully charged.

1.175-1.185 when half discharged.

1.100-1.110 when fully discharged.

Specific gravity of 1.230 means the electrolyte in

a fully charged battery is 1.230 times heavy as

an equal volume of pure water when both theliquid are at the same temperature.

Hydrometer is used to measure it.


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A-Hydrometer , B-Battery

Hydrometer consists of glass barrel and bulb syringe for sucking up anelectrolytic sample. The depth to which the float sinks in the liquid indicates

specific gravity of the liquid (electrolyte)


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Charging process

Check the level of electrolyte. If it is below thetop edge of the plates, add more electrolyte till it

is about 10mm above it. Connect negative and positive terminal of

battery to respective terminals of batterycharger.

Adjust the value of charging current. (for xplates battery, charging current should be x/2)

Continue charging till gassing begins


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Battery voltage Open circuit voltage of fully charged

battery cell is about 2 volts.

In a 6 V battery, there would be 3 cellsconnected in series similarly in 12 Vbattery, there will be 6 cells connected inseries.

Older automobiles used 6 V battery. Latestmodel use 12 V battery.


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Battery capacity

1)No. of plates

2)Area of plates

3)Quantity of electrolyte

4)Temperature

About 930 sq cm of plate surface must be in contact with the

electrolyte to produce 40-60A of current. Six volts battery have 15,

17, 19 and 21 plates per cell and 12 V battery have 7, 9, 11 and 13

plates per cell. There is always one more negative plate than

positive plate. Between 2 negative plates, there is one positive plate.

It is defined as amount of current it can deliver which maydepend on:


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Battery rating

Batteries are rated according to following standards recommended by

SAE and AABM:

20-hour rating( in Ampere-hours): It indicates thelighting ability of a fully charged battery. It is obtained by dischargingthe battery at a current rate equal to 1/20 of the manufacturers

ampere-hr rating.

Cold rating: It indicates the no. of minutes of a 6 V battery candeliver 300A at 0 F before the cell voltage drops below 1 V. It gives

the indication of cold weather starting ability of the battery.

(NOTE: an ampere-hr is the quantity of electrical energy

furnished by a current of 1 A for 1 hr)


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Battery troubles Self discharging

Sulfonation( when a battery discharges, the leadsulphate forms and deposits on the plates. When it isrecharged, lead sulphate converts again into activematerials-lead peroxide and spongy lead)

Internal short circuiting( due to damagedseparators or dropping of active material from the plateswhich forms heap so high to make short circuit)

Deterioration of plates

Cracking of container


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Factors affecting battery life Overcharging: overcharging decompose water of electrolyte intohydrogen and oxygen gas. Gas bubbles tend to wash active materialfrom the plates and carry moisture and acid from the cells as a finemist.

Undercharging: a battery operated in an undercharged conditionis not able to deliver full power and is liable to freeze during severewinter weather.

Lack of water: water, if not replenished as the liquid level falls tothe top of separators, and the plates are soon exposed, the acid willreach a dangerously high concentration that may charge anddisintegrate the separators and may permanently impare the

performance of the plates. Excessive load: a battery should never be used to propel the car

by use of starting motor with clutch engaged except in greatemergency. This may damage the starting motor by producing highinternal battery temperature.

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Battery Used in Automobiles