THE AUTOMOTIVE BATTERY

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THE AUTOMOTIVE BATTERY
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What is the purpose of the battery in a car?

• Provide voltage and current for the starter motor
• Provide voltage and current for the ignition
  system during cranking
• Supplies all electrical power when the charging
  system is not operating
• Acts as a voltage stabilizer for the charging
  system
• Provides extra current for short periods of time
  while the charging system is catching up to a new
  load

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BATTERY OPERATION

• The automotive battery is an electrochemical
  device that provides a potential difference.
• Automotive batteries are made up of a series of
  secondary cells that can be recharged.
• The battery does not store electrical energy, it
  stores chemical energy that is converted to
  electrical energy as it discharges.

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What is needed for an
electrochemical reaction to occur?

• Two unlike metals in a conductive and reactive
  solution (electrolyte)
• A battery cell is made up of spongy lead, lead
  peroxide and an electrolyte of sulfuric acid and
  water.
• This kind of battery is called a lead-acid
  battery.
• The spongy lead (Pb) is the negative material.
• The lead peroxide (PbO2) is the positive
  material.
• The electrolyte is 64 water (H2O) and 36
  sulfuric acid (H2SO4) when the battery is fully
  charged.

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The Discharge Charge Process

• As the battery discharges, a chemical reaction
  occurs which releases electrons from the lead
  (Pb) and causes the lead peroxide (PbO2) to gain
  electrons.
• During this process both of the materials are
  changing to lead sulfate (PbSO4) and the
  electrolytes acid is changing to water (H2O).
• As the battery is recharged the reaction is
  reversed and the materials and electrolyte return
  to their original states.

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The process of discharging and recharging
is called cycling.

• Discharging Reaction
• Pb H2SO4 Þ PbSO4 H2 2 electrons
• PbO2 H2SO4 2 electrons Þ PbSO4 H2O O2
• Recharging Reaction
• PbSO4 2 electrons H2 Þ Pb H2SO4
• PbSO4 (-2 electrons) H2O O2 Þ PbO2 H2SO4

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Voltage

• Each battery cell produces 2.1v during the
  discharge reaction.
• Cells are connected in series to gain the desired
  battery voltage.
• 3 cells yield 6.3v
• 6 cells yield 12.6v
• Charging voltage needs to be 1 volt or more above
  battery voltage to reverse the reaction.

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Battery Construction

• Cells are made of positive and negative plates
  which are kept from touching by a porous
  separator material, usually plastic or
  fiberglass.
• The plates are made on a lead alloy grid which
  holds the spongy lead or lead peroxide material.
• The positive grids are connected together with a
  post strap. The negative grids are also
  connected together. The grids carry the cell
  current to the battery posts.
• The battery case is divided into cell cavities
  which hold the electrolyte and the plate groups.
  The plate group from one cell is connected to
  another cells plate group through a hole in the
  cell wall.

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Battery Varieties

• Cycling Battery
• Designed to produce low current for long periods
  of time.
• They are usually very discharged before
  recharging.
• Plate material is thicker than an automotive
  battery.
• Starting Battery
• Designed to produce high current for very short
  periods of time.
• There is usually only a slight discharge before
  recharging.
• Plate material is thinner to reduce heat
  generation.

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Battery Types

• 1. Non-maintenance Free -
• Lead-antimony grid
• Removable vent caps use to inspect electrolyte
  and add water.
• 2. Low-maintenance -
• Hidden vent caps
• Lead - calcium or Lead - strontium grid which
  lowers electrical resistance and heat generation.
  This reduces gassing and electrolyte loss.

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Battery Types

• 3. Maintenance Free -
• No vent caps. The case has small vents at both
  ends.
• Grid similar to low-maintenance
• Envelope type separators keep loose plate
  material near plates

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Battery Types

• 4. Hybrid
• Lead - antimony in positive grid,
• Lead - calcium in negative grid reduces gassing
  and internal corrosion
• Spun glass separators allow for a more efficient
  chemical reaction
• These batteries are able to withstand more deep
  cycling

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Battery Types

• 5. Recombinant
• No caps or vents
• Gel type electrolyte
• Special envelope type separators allow hydrogen
  gas to be reabsorbed. No gassing
• Generate 13.2 volts with six cells

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Grid Types

• 1. Square Grid
• The grid frame is a pattern of squares or
  rectangles.
• Longer current path, high resistance
• 2. Diagonal Grid
• The vertical grid bars are set at diagonals to
  shorten the current path and lower resistance

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End Lesson One