In studying primary cells, you learned that chemical action is com- monly used as a source of electric power for emergency or portable equipment. However, it will furnish only a small amount of power and cannot be recharged. A storage battery of secondary cells can furnish large amounts of power for a short time and can be recharged.
Batteries of this type require more maintenance and care than dry cell batteries but are used widely in equipment where large amounts of electricity are needed for short periods of time. Secondary cells used in storage batteries are of the lead-acid type. In this cell the electrolyte is sulfuric acid while the positive plate is lead peroxide and the negative plate is lead. During discharge of the cell, the acid becomes weaker and both plates change chemically to lead sulfate. The case of a lead-acid cell is made of hard rubber or glass, which pre-vents corrosion and acid leaks. A space at the bottom of the cell collects the sediment formed as the cell is used. The top of the case is removable and acts as the support for the plates.
Since the active materials are not rigid enough to be mounted independently, a special grid structure of inactive metal is used to hold them. For maximum chemical action, a large plate area is desired, so each positive plate is interlaced between two negative plates. In a typical cell, you might find seven positive plates attached to a common support interlaced with eight negative plates attached to a different support.
Separators, made of wood or porous glass, hold each positive and negative plate apart but let the electrolyte pass through. The positive and negative plates are fastened to the case cover which is held in place by a special acid-resistant tar. An opening in the cover allows water to be added to the electrolyte to replace water which evapo-rates. The cap for this opening has a vent to allow gas to escape since the cell in operation forms gas at the positive plate. Since these cells furnish large amounts of electricity, they require larger terminals and leads. Connections and terminals are made of lead bars since other metals would corrode rapidly due to the acid electrolyte.
Storage Batteries:-
When two or more secondary cells are connected together, they form a storage battery. This battery stores electricity and can be recharged after discharge. Most storage batteries consist of three lead-acid cells in a common case permanently connected in series. Since each lead-acid cell is rated at about two volts, connecting three cells in series produces a battery volt-age of six volts.
also read....................What rules/precautions related to eating habits should be followed during cancer treatment in Ayurveda?
The symbol for a secondary cell is the same as that used for a primary cell and the storage battery symbol shows three cells connected in series. Storage batteries and secondary cells are not connected in parallel since a weaker cell would cause a stronger cell to discharge, thus lowering battery strength without the battery even being used.
Electric Power from Magnetism:-
The most common method of producing electricity used for electric power is by the use of magnetism. The source of electricity must be able to maintain a large charge because the charge is being used to furnish elec- tric power. While friction, pressure, heat and light are sources of elec-tricity, you have found that their use is limited to special applications since they are not capable of maintaining a large enough charge for electric power. All of the electric power used, except for emergency and portable equip- ment, originally comes from a generator in a power plant.
The generator may be driven by water power, a steam turbine or an internal combustion engine. No matter how the generator is driven, the electric power it pro-duces is the result of the action between the wires and the magnets inside the generator. When wires move past a magnet or a magnet moves past wires, electric-ity is produced in the wires because of the magnetism in the magnetic material. Now you will find out what magnetism is and how it can be used to produce electricity.
You must be logged in to post a comment.