Cells and Batteries

Cells and Batteries

1. Definitions

   • Cells
     • A device that changes chemical energ into electrical energy
       • primary cells are non-rechargeable
       • secondary cells are rechargeable and can be restored to full capacity
     • base cell construction
       • a cell consists of electrodes that are immersed in an electrolyte within some kind of container
         • difference in charge between the two electrodes causes an EMF to develop between the electrodes
           • adding plate mass increases the battery's ability to produce current over a longer period of time
           • adding plate area increases the battery's ability to produce high current for a short period of time
   • Battery
     • consists of a number of cells connected in series
     • Battery Resistance
       • cell componets are conductive; therefore, the cell will possess some resistance
         • no load connected to the cell, open circuit terminal voltage is = to the voltage produced
         • when a load is connected, a current will flow and a voltage drop will occur in the cell due to the internal resistance of the cell

2. Basic Primary Cells

   • non-rechargeable
     • used in flashlights, portable cd players, etc
   • examples of primary cells
     • Leclanche Cells
       • consisted of a carbon rod mixed with manganese dioxide
         • Now; a past made of zinc chloride and ammonium chloride as the electrolyte and zinc electrode
     • Alkaline cells
       • same as Leclanche but has better capacity

3. Lead-Acid cell

   • Secondary Cell
   • consists of lead peroxide and a spongy metallic lead
     • can be made into different designs for specific purposes and requirements
       • Found in electric vehicle power supplies, backup power supplies, emergency lighting and automotive starting
   • 3 types of lead-acid batteries
     • flooded cell
       • most common type of lead-acid battery
     • gelled electrolyte cell
       • virtually maintenance-free: gelled and does not leak or spill
         • corrosion resistant
       • has some problems
         • hydrogen and oxygen gases are emitted
           • can be highly explosive
     • absorptive glass mat cell
       • like gelled cell; virtually no maintenance required and no danger of spillage or gas emissions
         • have one-way valves that release gas pressure
       • the separator plate has a lower resistance than the plates of the gelled cell and lower volt drops

4. Nickel-Cadmium Battery

   • Secondary cell
   • made of nickel hydroxide and cadmium hydroxide
     • may be sealed or vented
       • Sealed are maintenance free
       • Vented require minimal maintenance
   • is a 10 cell battery. Each cell has a nominal voltage of 1.2V
     • advantages to lead-acid
       • higher energy to weight ratio
       • Recharges faster
       • longer storage lfie
       • low internal resistance, very high rates and good terminal voltage
   • used in rechargeable tools, laptops, and cameras

5. Lithium Battery

   • can produce voltages from 1.5V to 3V.
     • can store 150 watt hours in 1 kg of battery
   • the battery is pressurized
     • if it overheats, may explode
       • lightweight
         • has three components
           • positive electrode
             • lithium cobalt oxide
           • negative electrode
             • carbon
           • separator
             • very thin sheet of micro-perforated plastic
   • advantages
     • very lightweight
     • highly reactive element
     • holds their charge
     • no memory effect
     • disadvantages
       • degrade as soon as manufactured
       • very sensitive to high pressure
       • must be monitored, increases cost
       • overall price is expensive

6. Battery Ratings

   • Ampere-hour rating
     • indication of the total energy capacity of a battery
     • Current= Ah/time
   • Cold Cranking Amps
     • rating that indicates the current that can be drawn from a fully charged battery for 30 sec at a temp of 0 Farenheit
   • Reserve Capacity Rating
     • quoted in minutes

7. Internal Resistance

   • affects the terminal voltage under load conditions
     • considered to be in series with the cell
     • Formula: Vno load - Vwith load= Vdrop

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