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Battery : Theory and Practice

IntroductionThe battery is an electrochemical device. It converts chemical energy

into electrical energy. The battery produces electricity to operate thestarting motor and ignition system while starting the engine.

Discharging : Battery changes chemical energy into electrical energy- Current flow out of the battery

Charging : Electrical energy is converted into chemical energy- Battery stores the energy until it needed

The function of Battery

To operate starter motor ignition system E!I relays duringcran"ing of the engine

#upply all of the electrical power for the car whenever the engine isnot running

$elp the charging system in providing electricity when demand isabove the output of the charging system

#tore electrical energy for e%tended periods

&ct as a voltage stabili'er that smoothen the current through thevehicle electrical system

To allow dynamic memory and alarm system to remain activewhen the vehicle is left for a period of time

(nly the battery is the power supply

)hen engine is stopped the battery operates all electrical devices

)hen engine is started the battery operates the starter motor -discharged current flows from the battery

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)hen only the alternator is the power supply

&fter the engine starts the alternator operates all electrical devices* recharges the battery at the same time - charging current flowsinto the battery

)hen both are used as a power supply

+ight after the engine is started if the electrical load is too great forthe alternator the battery contributes electrical power - discharged

current flows from the battery

)hile the car is running almost all power is supplied by thealternator.

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Battery,s main function is to start the engine. &n imbalance in therelationship between the battery and the alternator may cause thebattery to become discharge

Construction of the Battery

&n automobile battery contains diluted sulphuric acid/ positive plates0 negative plates

Internally a battery is separated into several cells 1usually si% in thecase of automobile batteries and in each cell there are severalbattery elements all submerged in the electrolyte

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The positive plates and negatives plates are each connectedtogether by separate plate straps

These groups of positive and negative plates are then placedalternately separated by separators and fibreglass mats.

The plates separators and mats are called a battery element 2rouping the plates in this way serves to enlarge the contact area

between the active materials and the electrolyte allowing a greateramount of electricity to be supplied thus the battery capacity isincreased

3ositive 3lates

4ead pero%ide 1brown colour as active material formed on mesh 5

grid framewor" #trap together to form positive plate group

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#tandard car battery has .6/ mm grid thic"ness

(ne plate less as a common practice

7egative 3lates

3ure lead 1grey colour sponge lead as active material formed onmesh 5 grid framewor"

#trap together to form negative plate group

#tandard car battery has .89 mm grid thic"ness

(ne plate more as common practice

#eparator

Insulated and corrosion resistant material such as 3C paperbased glass fiber

;ust have correct pore structure for the electrolyte passage

3revent positive * negative plate from touching

2rid

To conduct electricity to and from active material and to support

the active material

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2rid is made of lead < antimony = but promotes electrolyte gassing1loss of electrolyte

2rid of lead < calcium is used for maintenance free battery -minimum loss of electrolyte

Electrolyte

#ulfuric acid * distilled water

Electrolyte that are used in batteries today have a specific gravity1#.2 of either ./> or ./? 1at /9@C when the battery is fullycharged 1 The difference is due to the particular ratio of distilledwater to sulphuric acid - the electrolyte having a #.2 of ./>contains >6A distilled water and 06A sulphuric acid while the

electrolyte having a #.2 of ./? contains >0A distilled water and0A sulphuric acid

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Specific Gravity (S.G)

The ratio of the density of a substance to that of

water. Water has a specific gravity of 1.0, so asubstance with a specific gravity of less than 1 is

less dense than water and one with a specific

gravity greater than 1 is denser than water.

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Specific Gravity

Container 5 battery case

3lastic container corrosion resistance material

It is divided into si% compartments or cells

pper and lower electrolyte level mar"ers are provided on thetranslucent battery case showing electrolyte level readily

The plates are raised up off the bottom of the case with ribs toprevent them from shorting out if any of the active materials shouldhappen to fall from the plates

ent 3lugs

ent plugs are caps for the holes that are used for addingelectrolyte

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They are also designed to separate the hydrogen gas 1from whenthe battery charges and sulphuric acid mist that are present in theair inside the battery by allowing the hydrogen gas to escapethrough the vent holes and the sulphuric acid mist to condense on

the sides of the vents and drop bac" into the battery

Battery Identification Codes

Batteries that are made in apan are given a battery identificationcode according to a apan Industrial #tandard 1I#

The code indicates the battery capacity dimensions and the positionof the positive terminal 1right or left side

Information of the ID Code

3erformance

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This indicates the battery,s capacity indirectly. The chart shows therelationship between battery identification codes and battery capacity.The capacity is e%pressed in ampere-hours

Battery )idth and $eight

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The battery,s width and height combination is indicated by one of theeight letters 1& to $

Battery lengthThe length of the battery is indicated roughly in centimetres 1cm. /0F inbattery identification code means that the battery is about /0 cm1/09mm long

3osition of the 3ositive Terminal

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The position of the positive terminal of a battery is indicated either by +1right side 4 1left side or blan"

!or Century Battery

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The electromotive force 1E;! generated by one cell isappro%imately /. regardless of the Guantity or si'e of the plates

#ince automobile batteries have si% cells that are connected inseries their nominal output E;! is about /

Discharging

The flow of current in the cell produces brea"down of the acid,s

sulphate #ulphate leaves and combines with the positive * negative plates

to form lead sulphate - so both plates are no longer dissimilar

(%ygen leaves the positive plates and returns to the electrolyte toform water

Charging

Current is force through in the battery - opposite direction tonormal

DC is reGuired to recharge If battery is / higher voltage is reGuired - 8

Charging action

!low of current brea"s up the electrolyte

Electrolyte o%ygen moves to combine with lead of the positiveplate to form lead pero%ide

Both plates give sulphate to form sulphuric acid

The negative plate form spongy lead-both plates are alteredchemically and concentration of the sulphuric acid increases

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Chemical reaction equationDischarging

OHPbSOPbSOHPbO24422

222 +++

ChargingPbSOHPbOOHPbSO +++

42224 222

Factors Affecting the Voltage of a Battery

Concentration of the acid in the electrolyte

as a rule of thumb the cell voltage is about 9.?8 < value of therelative density

&cid density Cell voltage Battery voltage A charge

./? /./ /. 99

./8 /.9? /.6 9

./9 /.98 /.0 69

.6 .HH /.9 /9

./ .H> .? 9

/ Terminal voltage must not be below .? 1minimum allowabledischarge

acid almost turn to water * lead sulphate crystal grow ma"ing itvery difficult to recharge the battery

0 Temperature

#tandard temperature are Guoted at 6@C

#2 falls by 9.99 per 9@C rise above 6@C

#2 rises by 9.99 per 9@C fall below 6@C

E%ample:

)hat is the #2 of an electrolyte at 86@C if the reading at /6@Cwas measured at .//

&ns: #2 at 86@C .// = 1/%9.99 #2 ./9>

8 E%treme temperature

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Chemical reaction slowed down - will not produced as muchcurrent

Engine difficult to start - thic" oil poor fuel atomi'ation heat loss

Battery Capacity Rating&ll si% cell storage batteries have the same voltage but they may have adifferent capacity. Capacity is a measure of how much current it canproduced and how long it can sustain this current

0 methods of defining battery capacity:

Reserve capacity rating

Defined as the time in minutes for the fully charged battery voltage tofall to 9.6 with a constant load of /6 & at /6@C - how long thebattery can sustain a /6 & discharge

/ Cold cranking amps !A" Cranking #erformanceThe current that the battery will give at -?@C for a specified intervalof time when the battery voltage falls to an end voltage - threestandard = B# 1British #tandard DI7 12erman #tandard and #&E1#ociety of &utomotive Engineers

#tandard Duration End oltage

B# >9 seconds ?.8 volts

DI7 09 seconds H.9 volts

#&E 09 seconds ./ volts

Battery si'eCC&

#tandard I# model

7#89J&4 0>B/9 /67#>9 8>B/8 0/6

7#9 >6D/> 8/9

79 >6D0 886

66D/0 66D/0 066

DI7 0>9

0 Ampere$%our rating

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&mount of energy measured in ampere-hours e%pected from a fullycharge battery until it become discharged down to .?

The discharge is measured in /9 hours

E%ample: a 69&h battery can e%pect to deliver /.6 &mpere for

/9 hours If a higher current were drawn e.g. 6 &mpere the theoretical

time would be 9 hours 1in actual it should be less = about ?hours

&h is used to estimate how long to charge a battery 1 notpopularly used now

In summary the capacity of a battery is the amount of electrical energythat can be obtained from it. It is usually given in ampere-hours 1&h

reserve capacity 1+C and cold cran"ing amps 1CC&

E%ample of 2erman #tandard

99 / >9&h 099&

!irst figure - manufacturer code

#econd figure - voltage

Third figure - capacity in ampere-hour

!ourth figure - cold cran"ing current

Internal Resistance&ll batteries have internal resistance but it is very low. eg. 9.996 ohm fora good condition battery and may be 9.96 ohm for a fair condition battery

The internal resistance of the battery causes the battery,s outputvoltage to decrease as the current passing through it increases

Battery with higher plates has lower internal resistance

&s battery age internal resistance increase

IrEV =

is actual terminal voltage theoretical voltager is internal resistance

!elf$discharge

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(ver a period of time a battery which is not used will gradually lose itscharge due to several factors

Internal chemical reaction due to antimony deposits on negative platetrace of iron in electrolyte

4ea"age currents due to dirt and fume to form conducting path #ediment at the bottom of the battery

#elf discharge at the rate of 9./A to A of the battery &h per daydepending on the age of the battery temperature antimony content

To avoid high temperature discharge

#tore in cool place

Charge battery every month if not use

(nce fully discharge it may not fully recover even after recharge

!ulphation

nder normal discharging fine crystals of lead sulphate are formed onthe plates and by charging these are convertible

If battery is left discharge for long period the crystal turns into coarselead sulphate which are not easily convertible

#ulphation causes the reduction in battery &h and also impede thecharging process causing the battery to become very hot

In minor sulphation cases e%tended period of charging at low currentwill improve but in serious cases the battery is condemned due tointernal short circuit

Battery Maintenance & Service

!afety Instructions & #rocedures

)hen handling sulfuric acid or when topping-up batteries which arenot maintenance-free with distilled water always wear protectivegoggles and rubber gloves

Do not fill up with electrolyte to above the ;&K mar"

Do not tilt battery to e%treme angles from the vertical for long periods

Due to the ris" of electrolytic-gas detonation smo"ing and na"ed

flames are not allowed and spar"s must be avoided when battery isbeing charged 1connect and disconnect cables in the prescribed orderwith the battery charger switched off

Battery charging rooms must be well ventilated

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7ever wear rings bracelets watches or hanging nec"laces around

battery

7ever lean over a charging battery

Do not charge a fro'en battery or a maintenance-free battery which

the charge-indicator dot shows light yellow or clear. The battery coulde%plodeL

7ever disconnect the positive cable first. If the wrench slips and

ma"es contact between the positive cable and ground a very highcurrent flows through the wrench. This action may heat the wrenchand burn your hand and possibly caused the battery to e%plode

Battery 'aintenance

Battery ;aintenance includes: ;a"ing visual inspection of the battery

Cleaning the battery top terminal and cable clamp

Testing the battery

Charging the battery

Battery isual Inspection4oo" for:

Electrolyte lea"age

Electrolyte level

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Crac" in the case 1may result from overtightening the hold-down

clams or top 1may result from using wrong wrench

4oose or missing hold-down clamps

4oose terminals 1may result from overtightening the cable bolts

Terminal corrosion

Cleaning the Battery

Corrosion around the terminals and clamps can be cleaned by using abattery-terminal brush 1with a solution of ba"ing soda and water

Battery Testing and Trou(le Diagnosis

The two main causes of battery troubles are overcharging andundercharging

(vercharging

Causes damage to the plate and shortens battery life. The high voltagecan also damage other electrical and electronic components!or a vent-cap battery - shown by freGuent addition of water!or a maintenance-free battery = shown by low electrolyte level

(ther signs of overcharging: oltage M 6 volt

Electrolyte dry too fast

igorous bubbles

3ungent smell

#urface always wet

Bulb always burnt

Battery buldge

ndercharging

3ossible causes include:

Charging system malfunction

Defective connections in charging system

E%cessive load demands on battery

Defective battery

#elf-discharge resulting from battery sitting idle for long periods

E%cessive "ey-off current drain

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Testing the Battery

Testing is done to determine whether a battery: Is in good condition/ 7eeds recharging0 Is defective and should be discarded

To test the state of charge - hydrometer for vent-cap battery- charge indicator for maintenance-free

batteryTo test for performance - battery load test

(pen-circuit oltage Test

!or maintenance-free battery that has no charge indicator (C can beused to measure the state of charge.;ade by measuring terminal voltage with digital multimeter(C /.8 volts and above = enough charge for load test(C less than /.8 volts charge the battery first

$ydrometer Test

Ball hydrometer = put the rubber tube into the electrolyte. #Guee'e andrelease the bulb. Electrolyte will be drawn into the tube. If the balls floatthe battery is fully charge. If none ball float the battery is discharge

!loat hydrometer = The same procedure applied. ;ar"s on the floatstem show the electrolyte #.2. The more fully-charged the battery the

higher the float

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Charge-indicator Condition

It is a built-in hydrometer to show the condition and state of charge ofthe battery. If the indicator is light yellow or clear the electrolyte level islow. Install a new battery

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Battery 4oad Test

&fter the battery passes the state of charge test chec" for theperformance by battery capacity test or battery load test. This measuresterminal voltage while the battery is discharging at high rate

To perform the testN

The load is applied using a tester that includes a voltmeter an ammeterand a carbon-pile resistor. The applied load is indicated onmanufacturer,s specification. #ome manufacturers recommendremoving the surface charge by applying a 099-ampere load to thebattery for 6 seconds. )ait 6 seconds before applying a load eGual toone-half the cold-cran"ing amps. &fter 6 seconds read the voltage andremove the load. Battery voltage should read H.> volts or higher. If belowthe minimum recharge the battery and retest it. If fails again discard thebattery

Battery Charging

& battery charger must be used if the alternator cannot charge thebattery adeGuately due to long period of no use

#low Charging

& slow charger feeds small amount of current into the battery. Chargingtime is longer 1about / hours at 9 amps. The chemical action inside

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the battery is improved and the active materials are plated bac" on thebattery plates better.

!ast Charging 5 Boost Charging

& fast charger forces a high current flow into the battery for rapidrecharging. !ast charging allow engine starting in a matter of minutes. &high charging current can be used below the gassing voltage. Ife%ceeded the battery starts to gas and leads to water loss in battery.Done for emergency case only because it can cause damage to battery

#tart &ssistant with umper Cables 5 ump #tart

The battery from another vehicle can be used to provide start

assistance. The procedure can only be used if the batteries are installedin both vehicles. !or efficient starting assistance use only standardi'edOumper cables 1DI7 /660 with conductor cross-section at least > mm/

from petrol engine and /6 mm/ for diesel engine. Both batteries musthave the same nominal voltage.T3rocedure for ump #tarting

Connect the positive terminal of the discharge batter y to the positive

terminal of the e%ternal power source

Connect the negative terminal of the e%ternal power source to a baremetallic surface away from the battery 1e.g. the engine ground strapon the vehicle receiving assistance

Chec" that battery Oumper cable are firmly attached

#tart the vehicle with the sound battery. &fter a brief pause also start

the disabled vehicle

(nce start assistance is complete disconnect the cable clamps in the

reverse order

Battery !torage

!or new batteryNnfilled : unlimited!illed conventional : 0 1ma% > months!illed completely maintenance-free : ? months

Battery must be stored in a cool and dry place and in a good state ofcharge

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Do not stac" batteries on top of each other without additional supportbecause the weight can collapse the case and the plates in the bottombattery

Removing and Replacing Battery

To remove a battery:Disconnect the ground cable from the batteryse a bo% wrench or battery pliers to remove a nut-and-bolt cable clamp4oosen the clamp bolt then pull the clamp from the terminalIf the clamp stic"s use a battery-clamp puller#Guee'e apart the ends of the rings with pliers to detach the spring-ringcable clamp

Disconnect the insulated cable from the battery4oosen the hold-down clamps and remove battery

To install the battery:Do not reverse the terminal connections+econnect the insulated cable first then the ground cableTighten the hold-down clamps but do not over-tighten

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