Battery Fundamentals Chapter 26

Objectives Describe battery parts and operation Understand how a battery converts chemical energy to electrical energy Explain battery capacity ratings Select the correct battery type to use in a variety of applications

Introduction Battery: heart of a vehicle's electrical system Converts electrical energy into chemical energy Converts chemical energy back into electrical energy Provides power to accessories Supplies current to the starter Acts like a capacitor Starter motor: largest load Draws more than 100 amperes Battery voltage is low after use

Battery Parts and Operation DC voltage Produced when two different metals are immersed in an electrolyte solution Automotive batteries Plates provide 2.1 volts Fully charged positive plate: combination of lead and oxygen (i.e., lead dioxide) Plates: grids with horizontal and vertical bars Battery's case filled with electrolyte mixture

Battery Parts and Operation (cont'd.) Battery cell Consists of a packet of several positive and negative plates Battery terminals Connections are made of lead Some batteries have side terminals Battery case Most are constructed of lightweight plastic Cell caps Most battery tops have removable cell caps

Battery Recharging and Discharging Current flows to battery from charging system Battery explosions injure 15,000 people a year Battery discharging Positive and negative plates become alike as the battery discharges Process is reversed during recharging After repeatedly charging and discharging Active material on the cell plates is worn

Battery Capacity Ratings Battery capacity is related to: Surface of plates Weight of active materials on plates Strength of electrolyte solution Cold cranking amps (CCA) rating Most common method of rating batteries Some manufacturers rate batteries in watt-hours Reserve capacity Indicates how long a vehicle can be driven after a charging system failure

Battery Types Batteries are designed for specific uses Deep-cycle: original battery design that was used in cars for many years Maintenance-free: have cell plates made of a slightly different material Low-maintenance: revision of the maintenance-free battery

Battery Plate Size Battery size is related to its reserve capacity Vehicles with larger engines and more accessories require batteries with more plate surface Recombination batteries Sealed batteries using electrolyte gel or microporous nonwoven glass Absorbed glass mat batteries Do not use free-liquid or gel electrolyte

Battery Selection BCI lists group numbers Considerations Indicate physical size of batteries Considerations Must fit the battery box Posts must be on the correct side of the battery Battery holddown must fit the battery Battery cannot be so high that it shorts on the hood

Battery Service Life Average battery Effects of sulfation Service life of three to five years Life is determined by amount of material shed from surface of positive plates Effects of sulfation Usually reversible Effect of temperature on batteries Batteries do not work well in cold weather Engine becomes harder to crank Battery that is not fully charged will freeze easier

Battery Cables Must be large enough to carry all current demanded by starter Large cable is connected directly to the starter Cables for 12-volt systems are usually four or six gauge Battery terminal clamps Made of plated steel, brass, or lead

Battery Holddowns Battery must be held in its tray Can fall out as the car travels over bumps Excessive vibration can harm the battery Holddowns are made of steel or plastic

Reasons for Battery Failure Include: Damaged battery case can leak electrolyte Undercharging can cause sulfation Overcharging can cause buckled and warped plates Vibration can cause more material to be shed from plates Internal shorts between the plates can cause a dead cell

Hybrid Electric Vehicle and Other Battery Types Other types of batteries include: Nickel metal hydride batteries Subject to memory effect Lithium-ion batteries Term used for all batteries that use lithium Typical hybrid battery Most hybrid automobiles use NiMH batteries Paper membranes absorb electrolyte Hybrid battery pack gets hot Has air cooling system