Batteries produce their power through a chemical reaction which is released when a load, such as a light globe, starter motor or electric fan, is connected to the battery. As was observed more than 100 years ago, when two different metals are placed in a liquid capable of conducting electricity, and the metals are connected together above the liquid, electrical current flows through the connection.
The different metals are referred to as electrodes. Pure lead is used for the negative electrode or plate and a lead dioxide paste is used for the positive electrode. When combined, they are referred to as a cell. Two or more cells connected together are called a battery. The liquid solution is called an electrolyte which consists of a diluted solution of sulphuric acid. The battery becomes discharged or flat when no more current flows through the cell. The cell can be recharged by forcing electrical current back through the cell in the reverse direction.
The chemical reaction that takes place during discharge converts both the positive electrode and the negative electrode to lead sulphate. Water is produced and dilutes the strength of the acid.
The chemical reaction is written as follows:
During recharge the electrodes are converted back to lead dioxide and lead. The water produced during discharge is consumed, returning the acid to its original strength. In addition, some electrolysis of the water in the electrolyte occurs breaking it down into its component gases, hydrogen and oxygen.
The rate at which the gasses are produced is greatest when the battery reaches a fully charged state. Also the higher the charging current, the more gas produced.
Batteries have a series of vent flues that allow the gas to escape the system. Hydrogen gas is highly volatile and sparks or flame can easily ignite the gas and cause an explosion. Therefore great care must be taken to adhere to established safety precautions, especially when recharging.
A battery’s electrical pressure or electromotive force is measured in volts. The flow of electrical current is measured in amperes. The mathematical relationship between electrical power and its components is as follows:
(Volts are represented by the symbol ‘V’, amps ‘I’ and power or watts ‘P’.)
P = IV
Watts = Amps x Volts
or Amps = Watts
or Volts = Watts
Also, “Ohm’s Law” expresses a mathematical relationship between volts, amperes and resistance (Ohms) in an electrical circuit.
Ohms = Volts
or Volts = Ohms x Amps
or Amps = Volts
This article is found in the Virtual mechanic CD Rom
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By Darren Gow-Brown, Melbourne Australia