chapter 07 bennet

8/10/2019 Chapter 07 Bennet

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Chapter 7

Batteries


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Objectives (1 of 2)

Define the role of a battery in a vehicleelectrical system.

Outline the construction of standard,

maintenance-free, and gelled electrolytebatteries.

Describe the chemical action within thebattery during the charging and discharging

cycles. Outline how batteries are arranged in multiple

battery banks in truck chassis.


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Objectives (2 of 2)

Verify the performance of a lead-acid battery usinga voltmeter, hydrometer, refractometer, and carbonpile tester.

Analyze maintenance-free battery condition usingan integral hydrometer sight glass.

Describe the procedure required to charge differenttypes of batteries.

Jump-start vehicles with dead batteries usinganother vehicle and generator methods.

Outline how batteries should be safely stored out ofchassis.


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Battery-operating Principles

A battery is a galvanic device.

The lead-acid battery is the electrical energy

storage device used on most vehicles.

It performs a secondary role as a stabilizer

for the voltage in the vehicle electrical

system.


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Battery Construction

Six series connected cells in a polypropylene

casing

Each cell has positive (anode) and negative

(cathode) plates.

The plates are arranged so that positive and

negative plates are located alternately with

each other. Each cell in a battery is separated by

partitions.


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Electrolyte (1 of 2)

It is any substance that conducts electricity.

It is the liquid solution that enables the

galvanic or chemical action of the battery.

It is a solution (mixture) of sulfuric acid

(H2SO4) and pure water (H2O).

The solution proportions should be 36

percent sulfuric acid and 64 percent distilledwater.


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Electrolyte (2 of 2)

This produces a specific gravity of 1.265 at

80Fahrenheit.

The acid-to-water proportions should never

be tampered with.

During discharge, the ratio of sulfuric acid to

that of water is reduced.

This reduces the specific gravity which can bemeasured with a hydrometer or refractometer.


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Specific Gravity and Temperature

Temperature directly affects specific gravity.

The hydrometer reading must always be

temperature adjusted.

To adjust specific gravity to temperature: Add 0.004 for every 10 degrees above 80

Fahrenheit.

Subtract 0.004 for every 10 degrees below 80

Fahrenheit. Electrolyte tested using a refractometer does not

require temperature correction.


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84 Factor

Specific gravity relates directly to cell voltage.

The 84 factor enables cell voltage to be

calculated by adding 0.840 to the specific

gravity measured.

If the specific gravity is 1.260, cell voltage

would be 1.260 + 0.840 = 2.100 volts.

The 84 factor is a ballpark method that doesnot apply to discharged batteries.


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Discharge Cycle

The lead peroxide (PbO2) on the positive plate

reacts with the sulfuric acid solution electrolyte

(H2SO4) releasing an oxygen molecule (O2) to the

electrolyte, forming water (H2O).

The negative plate (Pb) reacts with the electrolyte

to form lead sulfate (PbSO4).

This chemical action will continue until both the

positive and negative plates are coated with leadsulfate (PbSO2) and the electrolyte has been

chemically reduced to water (H2O).


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Charge Cycle

The sulfate coatings that have formed onboth the positive and negative plates arereacted to return them to the liquid

electrolyte. Water molecules in the electrolyte reduce to

hydrogen and oxygen.

Hydrogen combines with the sulfate in the

electrolyte to form sulfuric acid, while theoxygen is drawn to the positive plate toreconstruct the lead peroxide coating.


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Sulfation

When a battery becomes discharged, both plates

are coated with lead sulfate (PbSO4).

During the charge cycle, this sulfate coating is

converted back into electrolyte. When the sulfate coating hardens on the plates, it

can no longer be converted.

Battery output then becomes limited and the

condition progresses to complete battery failure. A failed battery is said to be sulfated.


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Maintenance-free Batteries

Substances such as calcium, cadmium, andstrontium replace antimony in the plates.

These substances reduce gassing.

There is not a means for adding water whichhas been depleted.

A low-maintenance battery is one that usesessentially the same construction as the

maintenance-free battery, but does providefor periodic inspection and replenishing of theelectrolyte.


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Gelled Electrolyte Batteries

A special electrolyte is used that liquefieswhen stirred or shaken, but when left at rest,returns to the gelled state.

In the charge cycle of the battery, the oxygenthat is released at the positive platerecombines within the cell with the hydrogenreleased at the negative plate.

The recombination of hydrogen and oxygenproduces water that is then reabsorbed to theelectrolyte.


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Battery Ratings

Cold-cranking rating

The current load a battery is capable of delivering for30 seconds at a temperature of 0F

Ampere-hour rating

The amount of current that a fully charged battery canfeed through a circuit before the cell voltage drops to1.75V (For a typical 12V battery, this would be equalto a battery voltage of 10.5V.)

Reserve capacity rating The amount of time a vehicle can be driven with its

headlights on in the event of a total charging systemfailure


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Battery Banks

Multiple batteries are

connected in banks.

Batteries may be

connected in series orparallel.


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Battery Maintenance

Neglect and abuse will

shorten battery service life.

The battery should be

inspected at each chassis

lubrication. Battery maintenance

includes inspecting the

battery and its mounting for

corrosion, loose mounting

hardware, case cracks, anddeformation.


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Winterizing Batteries

When winterizing batteries, disconnect battery

cables and load test each battery individually.

Because it is important to keep batteries warm to

optimize performance in cold weather, many trucksare equipped with battery heaters.

If you suspect a battery is frozen, do not attempt to

heat it rapidly.

Trickle charge and observe for charge response.


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Battery Testing

A complete battery test includes these steps:

1. Visual inspection

2. State of charge test

3. Battery capacity (load) test


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State of Charge Test (1 of 3)

Measure and recordspecific gravity,corrected to 80F.

If specific gravity

readings are 1.225 orhigher and are within50 points (0.050specific gravity)

between the highestand lowest cells,proceed to the loadtest.


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If specific gravity readings

are low (below 1.225) or

vary more than 50 points

between highest and lowest

cells, recharge the batteryand retest.

If, after charging, specific

gravity readings are greater

than 50 points between

highest and lowest cells,replace the battery.


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Integral hydrometers

On many sealed maintenance-free batteries, a

temperature-compensated hydrometer is built

into the battery cover. Green dot = 65% or greater charged

Dark = 65% of less charge

Clear = low electrolyte level


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Open Circuit Voltage Test (1 of 3)

1. Remove surface charge; crank the engine

for 15 seconds.

Do not allow the engine to start.

To prevent the engine starting, apply theengine stop control or disconnect the fuel

solenoid valve lead wire as required.

See Table 7-1 on page 195 of textbook.


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2. After cranking the

engine, allow the

battery to rest for 15

minutes.

3. Connect the

voltmeter across the

battery terminals to

determine the batterystate of charge.


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4. If the stabilized voltage is below 12.4 volts,

the battery should be recharged.

Also, inspect the vehicles electrical system

to determine the cause of the low state ofcharge. After charging the battery, proceed to

the load test.


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Load Test


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Electrochemical Impedance

Spectroscopy (EIS)

EIS evaluates the electrochemical

characteristics of a battery by applying

alternating current (AC) at varying

frequencies and measuring the currentresponse of the battery cell.


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Conductance Testing (1 of 2)

In the trucking industry, modified EIS testing

has become known as conductance testing

or AC conductance testing.

These test instruments have been proven tosignificantly reduce the incidence of incorrectly

diagnosed battery problems.

The advantages of AC conductance testing

are that it is noninvasive and quick, and test

instruments are inexpensive.


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Conductance Testing (2 of 2)


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Charging the Battery

There are two methods of recharging a

battery:

The slow-charge method

The fast-charge method

Either method can be used to recharge most

batteries.

However, there are some batteries that mustbe charged slowly.


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Caution

Hydrogen gas may be discharged during

charging and care should always be taken

when connecting or disconnecting battery

terminals not to create a spark that couldresult in a battery explosion.

Always disconnect the ground cable first and

reconnect it last.


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Charging the Battery

Fast-charging


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Jump-starting


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Shop Talk

Frequent need for refilling battery cells is a

typical indication that the batteries are being

overcharged.

Test the charging system and adjust thevoltage regulator as needed.


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Tech Tip

To obtain an accurate reading on a

refractometer, it is necessary to view the

reading in good light.

Attempting to read a refractometer in poorlight will make it difficult to read the refractive

scale.

W i


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Warning

Never jump-start or attempt to recharge afully discharged maintenance-free battery.

Jump-starting and charging can create an

explosion hazard. These batteries have limited means to vent

gas build-up and therefore should be replaced

if fully discharged.

C ti


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Caution

Do not overcharge batteries, particularlymaintenance-free type batteries.

Overcharging causes excessive boil-off of

water from the electrolyte. Overcharging also causes the battery to

produce explosive combinations of hydrogen

and oxygen.

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Shop Talk

Batteries with charger indicators cannot becharged if the indicator is clear or light in

color; replace these batteries.

C ti


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Caution

If smoke or dense vapor comes from thebattery, shut off the charger and reject the

battery.

If violent gassing or spewing of electrolyteoccurs, reduce or temporarily halt the

charging.

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Shop Talk

Ensure that the vehicle with the deadbatteries and the boost vehicle do not directly

contact.

If the two vehicles are in contact, a groundconnection could be established, which could

cause sparking when jumper cables are being

connected.

Sh T lk


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Shop Talk

The ground connection must be sound. Itused to be recommended that you not

connect directly to the ground post of the

discharged battery. Due to the sensitivity ofelectronic control modules connected to the

chassis data bus, OEMs today suggest that

ground clamps always be connected directly

to battery ground.

Warning


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Warning

Make sure that the clamps from one cable donot contact the clamps on the other cable.

Wear safety glasses, and do not lean over

the batteries when making connections.

Summary (1 f 7)


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Summary (1 of 7)

A battery converts chemical energy into electricalenergy.

A battery is a galvanic device.

The storage device for electrical energy on current

trucks is the lead-acid battery. A lead-acid battery acts as a sort of electron pumpin a truck electrical circuit.

A typical battery contains anode (positive) andcathode (negative) plates arranged in cells that are

grouped in series within the battery housing. The electrolyte used in lead-acid batteries is a

solution of distilled water and sulfuric acid.

Summary (2 f 7)


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Summary (2 of 7)

The electrolyte in a lead-acid battery is bothconductive and reactive.

During the discharge cycle of the battery, lead

peroxide on the anode (positive plate) combines

with electrolyte, releasing its O2into the electrolyte

to form H2O or water. Meanwhile, lead on the

cathode (negative plate) reacts with electrolyte to

form lead sulfate (PbSO4). The result of discharging

a battery is lead sulfate formation on both the

anode and cathode plates.

Summary (3 f 7)


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Summary (3 of 7)

During the charge cycle, the sulfate coating on theanode and cathode plates is drawn off and

recombined into the electrolyte.

Charging reestablishes the correct proportions of

sulfuric acid and water in the electrolyte.

A fully charged battery has an electrolyte solution

that consists of 36 percent sulfuric acid and 64

percent pure water.

A fully charged battery should produce a specific

gravity reading of 1.260 at 80F.

Summary (4 f 7)


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Summary (4 of 7)

During the charge cycle, both oxygen and hydrogenare released from electrolyte in a process known asgassing.

In maintenance-free and low-maintenance batteries,

the results of charge gassing are contained in acondensation chamber.

Gel cell batteries are designed to sustain deepcycling and are used in truck electrical systemsrequiring an isolated battery to power auxiliaryaccessories during shutdown.

Gel cell batteries should be recharged by directconnection to the battery charger.

Summary (5 of 7)


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Summary (5 of 7)

Only approved chargers may be used to charge gelcell batteries.

These regulate the charging voltage to between13.8V and 14.1V. Most battery chargers use a

charging voltage of about 16V, which can destroy agel cell battery.

On trucks equipped with gel cell batteries, thevoltage regulator must be set at 14.1V or less.Voltages higher than 14.2V can destroy gel cell

batteries.

Batteries are performance rated by cold-crankingamps, reserve capacity, and ampere-hour rating.

Summary (6 of 7)


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Summary (6 of 7)

Most truck batteries are specified to a chassiselectrical system by their cold-cranking amp (CCA)rating.

Temperature has to be considered when evaluating

the output capacity of any battery. Available cranking power significantly drops as

temperature falls.

When removing a battery from a vehicle, always

disconnect the ground cable first. Battery electrolyte should be tested with either a

refractometer or a hydrometer.

Summary (7 of 7)


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Summary (7 of 7)

When jump-starting vehicles, be sure to study thebattery configuration on both vehicles beforeattempting to make electrical connections. Alsoswitch off all the chassis electrical loads beforeconnecting jumper cables.

Generator charging is popular and effective, butensure that the correct procedure is followed beforeusing this method of charging.

Capacitance testing using instruments such as theMidtronics 700 is commonly used to assess batteryserviceability.

Battery performance is best tested using a digitalAVR.

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