1. Cells and Batteries

2. Learning Objectives  To identify different types of cells  To describe the characteristics of each type of cell  To describe the advantages and disadvantages of each type of cell  To describe how a fuel cell works and how it can be useful for microgeneration

3. Primary Cells

4.  Primary cells are single use, non- renewable cells  They are available in a number of sizes and capacities as well as different chemistries  The most popular primary cell is the AA battery.

5. Types of primary cell

6.  These include zinc-carbon, alkaline, zinc-air, mercury and Leclanche cells.  Each of these cells uses slightly different chemistry to produce electricity from the chemical reaction within it.

7. Zinc Chloride Cell Alkaline Cell

8. Characteristics of cells

9.  Primary cells generally operate at 1.5v with a variety of capacities from 500mah to 3000mah  They tend to deliver power at gradually decreasing rate so they gradually wear out rather than suddenly fail.  However they are able to store large amounts of energy over long periods of time with low levels of self discharge ensuring a good shelf life

11. Secondary cells

12.  Secondary cells differ from primary cells in that they are reuseable.  Once the reaction has been exhausted in a secondary cell, an electrical current can be used to re-energise the cell and reverse the electrochemical reaction  They are available in similar sizes to primary cells and can be used as direct replacements for primary cells in most cases

13.  There are several different types of chemistry found in secoondary cells. The main types are Nickel-Cadnium, Nickel metal-hydride, Lead Acid and Lithium polymer

14. Nickel Cadnium Ni-MH cell Lithium Polymer

15.  The main advantage of secondary cells is that they are able to be reused many times unlike primary cells  However, they do not deliver the same voltage as primary cells (1.2v vs. 1.5v), Ni- Cd cells are subject to memory effect, Ni- MH cells are susceptible to high charge rates, they have higher self discharge rates that lead to short shelf lifes although their energy density can be much higher

17. Fuel Cells

18. Look at the following weblink  http://americanhistory.si.edu/fuelcells/bas ics.htm http://americanhistory.si.edu/fuelcells/bas ics.htm