1. THE AUTOMOTIVE BATTERY

2. 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

3. 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.

4. 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 (PbO 2 ) is the positive material. The electrolyte is 64% water (H 2 O) and 36% sulfuric acid (H 2 SO 4 ) when the battery is fully charged.

5. The Discharge – Charge Process As the battery discharges, a chemical reaction occurs which releases electrons from the lead (Pb) and causes the lead peroxide (PbO 2 ) to gain electrons. During this process both of the materials are changing to lead sulfate (PbSO 4 ) and the electrolyte’s acid is changing to water (H 2 O). As the battery is recharged the reaction is reversed and the materials and electrolyte return to their original states.

6. The process of discharging and recharging is called cycling. Discharging Reaction: –Pb + H 2 SO 4  PbSO 4 + H 2 + 2 electrons –PbO 2 + H 2 SO 4 + 2 electrons  PbSO 4 + H 2 O + O 2 Recharging Reaction: –PbSO 4 + 2 electrons + H 2  Pb + H 2 SO 4 –PbSO 4 (-2 electrons) + H 2 O + O 2  PbO 2 + H 2 SO 4

7. 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.

8. 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 cell’s plate group through a hole in the cell wall.

10. 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.

11. 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.

12. 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

13. 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

14. 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

15. 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

16. End Lesson One