Automotive
 Car Battery

• An automotive battery is an electrochemical device that stores and provides electrical energy.  When the battery is connected to an external load, an energy conversion occurs that result in current flow through the circuit to the operate the load.  Electrical energy is produced in the battery by the chemical reaction that occurs between two dissimilar metal plates that are immersed in a electrolyte solution (common refered to as battery acid).

• When the battery is discharging, it changes chemical energy into electrical energy.  It is through this change that the battery releases stored energy. 

• During charging, electrical energy is converted into chemical energy.  As a result, the battery can store energy until it is needed.

• The Largest demand placed on the battery occurs when it must supply current to operate the starter motor.  After the engine has started, the vehicle's charging system recharges the battery.  It also provides the power to run the electrical accessories. If the vehicle's charging system fails, the battery must supply all the current needed to run the vehicle.  Most batteries can supply 25 amperes for two hours before they become so low that they are unable to keep the engine running. 

• The automotive battery has three main functions.
• 1. To provide voltage and serves as a source of current for starting, lighting, and ignition.
  2. It acts as a voltage stabilizer for the entire electrical system of the vehicle.
  3. It provides current whenever the vehicle's electrical demands exceed the output of the charging system.  

• The battery must be able to maintain a good charge when the engine is off.  The condition of the battery determines this capability, as do the electrical demands of the vehicle.

• When the engine is off, electrical power is still needed to maintain the memory in the various computers used in the vehicle and to keep clocks going.  The electrical loads present when the ignition switch is off are called parasitic loads.
  
  

Battery Construction 

• The storage battery consist of grids, positive plates, negative plates, separators, elements, electrolyte, cell covers vent plugs and cell containers.
  
• • An element is a group of positive and negative plates.
  • Grids form the basic framework of the battery plates.
  • Like plates are welded to a lead alloy post or plate strap.
  • Separators are porous plastic sheets that allow the transfer of ions between plates but prevent physical contact between them, which would cause the plates to lose their stored energy.
  • When the element is place inside the battery case and immersed in electrolyte , it become a cell.
    
• The battery has two external terminals: a positive (+) and a negative (-).  these terminal are either two tapered post, L terminals, threaded connectors on top of the case, or two internally threaded connectors on the side.  The terminals have either a positive (+) or a negative (-) marking, depending on which end of the series they represent.

Battery Hardware

• Battery Cables -  Battery cables must be of sufficient capacity to carry the current required to meet all demands.  The normal 12 volt cable size is 4 or 6 gage.  Various forms of clamps are used to ensure a good electrical connection at each end of the cable.

• Battery Hold-Downs - All batteries must be held securely in the vehicle to prevent the possibility of shorting across the terminals if they move or fall.  Normal vibrations cause the plates to shed their active materials.  Hold-downs reduce the amount  of vibration and help increase the life of the battery.  Battery hold-downs are made of metal or plastic.

Battery Voltage and Capacity

• Cell size, state of charge, rate of discharge, battery condition and design, and electrolyte temperature all strongly influence the voltage of a cell during discharge. When cranking an engine, the voltage of an average battery at 80⁰ F may be about 11.5 to 12 volts.  At 0⁰ F the voltage is significantly lower.
• At low temperatures, the viscosity of the electrolyte increases, making it more difficult for the acid to move freely into the plate pores and around the separators.  This slows the rate of the chemical reaction and lowers battery voltage, limiting the output of the battery, especially at cranking rates.
• Battery capacity is the ability to deliver a given amount of current over a period of time.  It depends on the number and size of the pates used in the cells and the amount of acid used in the electrolyte.

Battery Size Selection

• Besides selecting a battery based on its capacity and rating, the proper battery is also one that fits.  The battery should fit the battery holding fixture and the hold-down must be able to be installed.  It is also important that the height of the battery not allow the terminals to short across the vehicle's hood when it is closed.

Factors Affecting Battery Life

• All storage batteries have a limited service life, but many conditions can decrease service life.
   
• • Improper Electrolyte Levels - With nonsealed batteries, water should be the only portion of the electrolyte lost due to evaporation during hot  weather.  Maintaining adequate electrolyte level is the basic step in extending battery life for these designs.
  • Temperature - Batteries do not work well when they are cold.  At 0⁰ F a battery is only capable of working at 40% of its capacity.  There is a possibility that the battery will freeze when it is low on charge and subjected to very cold weather.  When the weather is extremely hot, there is a possibility of boiling over.
  • Corrosion - Battery corrosion is commonly caused by spilled electrolyte or electrolyte condensation from gassing. In either case, the sulfuric acid from the electrolyte corrodes, attacks and can destroy not only connectors and terminals but hold-downs straps and the battery tray as well, which can result in physical damage to the battery.
  • Poor Mounting - Loose hold-downs straps allow tahe battery to vibrate or bounce during vehicle operation.  This vibration can shake the active materials off the grid plates, severely shortening battery life. It can also loosen the plate connections to the plate strap, loosen cable connections, or even crack the battery case. 

Other readers found these articles interesting as well.

  Battery Service

  Electricity

  Hand Tools

  Safety First