Batteries

1
Batteries

• Purpose
• Construction
• How it works
• Failures
• Ratings
• Testing and maintenance
• Jump starting

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Purpose

• Provide power for starting engine
• Provide extra power when demands exceed
  generators capabilities
• Stabilizes system voltage by providing a
  reservoir for excess voltage from charging system

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Construction

• Inside plastic case are 6 cells composed of
  positive and negative plates
• Plates are supported by plastic ribs in case
• Plates are constructed on a grid made primarily
  of lead
• Battery grids hold the active material and
  provide the path for current created in the plate

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Construction
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Construction

• The battery plate creates electrical energy from
  chemical energy and this current must flow from
  where it is generated to where it is connected to
  the outside post

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Construction

• The positive plates are pasted with lead dioxide
• The negative plates are pasted with sponge lead
• The positive and negative plates are installed
  next to each other without touching

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Construction

• Cells are constructed with porous separators
  between the positive and negative plates to
  prevent touching and short circuits
• Each cell produces 2 volts regardless of the
  number of plates
• The greater number of plates in each cell, the
  greater amount of current can be created

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Construction

• Each cell is separated by a partition made of
  plastic
• Electrical connections are made by lead
  connectors that loop over the top of each
  partition and connect the plates together

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Construction

• Positive (lead dioxide) and negative (lead)
  plates are surrounded by electrolyte
• Electrolyte is composed of 36 sulfuric acid and
  64 water (H2SO4)
• The difference in potential (voltage) between
  lead peroxide and lead in acid is 2.1 volts
• This is known as a lead-acid battery

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How it works

• During discharging the lead dioxide combines with
  the electrolyte and releases oxygen into the
  electrolyte to form water
• The lead combines with the electrolyte to become
  lead sulfate
• When the battery becomes fully discharged, both
  plates become lead sulfate and the electrolyte
  becomes water
• Batteries can freeze when they are discharged

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How it works

• During charging the sulfate leaves both the
  plates and returns to the electrolyte
• The electrolyte returns to sulfuric acid
• The positive plates return to lead dioxide
• The negative plates return to pure lead

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How it works

• When the battery is discharging, the acid leaves
  the liquid and is deposited on the plates
• When the battery is charging, current flows into
  the battery and forces the acid from the plates
  and back into the liquid

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Failures

• Causes of failure
• Overheating caused by overcharging
• Causes the plates to warp
• Can damage the battery case
• Overcharging can cause the active material to
  disintegrate and fall from the plates
• Vibration
• Cycling
• Also causes active material to fall from the
  plates

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Ratings

• Cold cranking amps (CCA) the number of amps that
  can be supplied by the battery at 0 deg. F for 30
  seconds while the battery maintains a voltage of
  at least 1.2 volts per cell
• Reserve capacity (RC) the number of minutes for
  which the battery can produce 25 amps and still
  maintain 1.75 volts per cell

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Ratings

• The capacity of any battery is determined by the
  amount of active material in the battery
• A battery with a large number of thin plates can
  produce high current for a short period
• A battery with few thick plates can produce low
  current for a long period

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Testing and maintenance

• Symptoms of a weak battery
• Using water in one or more cells
• Excessive corrosion on battery cables or
  connections
• Slower than normal engine cranking

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Testing and maintenance

• Electrolyte should never be added to a battery
• Adding electrolyte increases the acid content and
  will shorten the life of the battery
• Add distilled water to each cell to 11/2 inches
  below the top of the filler tube or until the
  plates are covered

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Testing and maintenance

• The amount of sulfate in the electrolyte is
  indicated by the electrolytes specific gravity
• Specific gravity is the ratio of the weight of a
  given volume of a liquid to the weight of an
  equal volume of water
• Pure water has a specific gravity of 1,000 at 80
  deg. F
• Electrolyte has a specific gravity of 1.260 to
  1.280 at 80 deg. F

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Testing and maintenance

• The most accurate test for battery condition is a
  load test
• For accurate results, the batterys state of
  charge must be determined before load testing
• State of charge can be determined by measuring
  specific gravity
• State of charge can also be determined by an open
  circuit voltage test

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Testing and maintenance

• specific battery state of
• gravity voltage charge
• 1.265 12.6 100
• 1.225 12.4 75
• 1.190 12.2 50
• 1.155 12.0 25

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Testing and maintenance

• A battery that has just been charged will have a
  surface charge
• A surface charge is a charge that is on the
  surface of the plates and will show as a higher
  than normal voltage
• A surface charge can be removed by turning on the
  headlights or loading the battery for 1 minute

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Testing and maintenance

• Load testing amount of load to be placed on
  battery is one half of the CCA rating for 15
  seconds
• If the battery can maintain 9.6 volts during the
  test, the battery is good
• If the battery voltage falls below 9.6 volts
  during any part of the test, it is defective

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Testing and maintenance

• The load is placed on the battery with a carbon
  pile
• Connect the voltmeter leads to the battery and
  clamp the inductive pickup over one of the
  battery cables
• Apply the load and observe the voltmeter

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Testing and maintenance

• Vehicles with two batteries wired in parallel
  should be disconnected and tested separately
• If one battery is found to be defective, it is
  strongly recommended that both batteries be
  replaced as a pair
• If a defective battery is left connected to a
  good battery, the defective battery will
  discharge the good battery

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Testing and maintenance

• Capacitance testing a testing device sends a
  signal through the battery to test the
  capacitance of the cells
• The unit can normally detect the CCA, state of
  charge and voltage of the battery
• This type of tests results can be incorrectly
  reported if the connections to the battery are
  faulty

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Testing and maintenance

• Always use adaptors on side post batteries
  whenever charging or testing
• The use of 3/8 bolts are not sufficient for
  charging or testing because only the threads
  contact the battery terminal
• Always disconnect battery cables on side post
  batteries when checking for corrosion

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Testing and maintenance

• Parasitic load tests use an inductive pickup or
  an ammeter wired in series
• Maximum allowable drain 50mA (.05 A)
• Common problems
• Underhood light staying on
• Glove compartment light
• Trunk light
• Aftermarket stereos (remote mounted CD changers)

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Testing and maintenance

• To find parasitic draws
• Disconnect fuses one at a time
• Disconnect generator
• Disconnect starter solenoid

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Testing and maintenance

• Before disconnecting battery cables on a vehicle
  
• Check stereo system for security code
• If system requires a code to be entered once
  power is restored, make sure you have the code
  before disconnecting power
• Do not attempt to enter incorrect codes

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Testing and maintenance

• Charging
• It is always best to slow charge (5 amps)
• Fast charging can overheat and damage battery
• Fast charging also increases release of hydrogen
  and oxygen gases from the battery
• Never allow the battery temperature to exceed 125
  deg F

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Testing and maintenance

• When connecting a charger
• Always make sure ignition is OFF
• Connect the cables to the battery before plugging
  in charger

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Jump starting

• Both vehicles OFF
• Connect positive cables
• Connect negative cable to good battery
• Connect negative cable to defective vehicles
  engine or metal bracket
• Start engine on good vehicle only if needed
• Disconnect in reverse order

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