Electrical Engineering ⇒ Topic : Types of Cells
Types of Cells
Using various metals and methods of construction, a large variety of cells has been developed.However, the cells can be divided into two main classes viz.
1. Primary cells
2. Secondary cells
Primary cells. A cell in which chemical action is not reversible is called a primary cell e.g., Voltaic cell, Daniel cell, Lachlanche cell, dry cell etc. As a primary cell delivers current, the active materials are used up. When the active materials are nearly consumed, the cell stops delivering current. In order to renew the cell, fresh active materials are provided. Another drawbackof a primary cell is that it cannot provide large and steady current for a longer period. This fact makes the primary cell rather an expensive source of electrical energy. Due to these drawbacks, the use of primary cells is limited to torch batteries and for experimental purposes in the laboratories.
(2) Secondary cells. A cell in which chemical action is reversible is called a secondary cell or storage cell. A secondary cell operates on the same principle as a primary cell but differs in the method in which it may be renewed. In a secondary cell, there is no actual consumption of any plate and that the chemical process is reversible. When the cell is delivering current (i.e discharging), the chemical action changes the composition of plates. When the cell is exhausted, the chemical action can be reversed (i.e., plates can be restored to the original condition) by passing current through the cell in the reverse direction to that in which the cell provided current. This process is called charging.
In other words, charging process reverses the chemical action and enables the plates to acquire original compositon. There are several types of secondary or storage cells; the more common ones being :
Note. When a secondary cell is charged, electrical energy is converted into chemical energy which is stored in the cell. When the cell discharges, the stored chemical energy starts converting into electrical energy.For this reason, a secondary cell is sometimes called a storage cell
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