In terms of electricity generation, in its simplest forms, an electric generator is a device converting mechanical energy into electrical energy with minimum loss of power. The source of mechanical energy may be a turbine or an internal combustion engine and is responsible for the amount of electricity generated. The output electrical energy is obtained by the operation of two forces; a rotating magnetic field with stationary armature or vice versa. In case of automobiles, an AC Generator or an Alternator charges the battery. It works on the principles of Faraday’s Law. When a current carrying conductor is placed in the influence of magnetic field, electromotive force is generated. This EMF is the AC voltage that is further converted to DC using commutator and brushes.
The construction of a modern day ‘Compact Alternator’ used in our cars involves an iron core on the rotor with a single layer of coiling. It produces multi-pole fields which create a strong electromagnetic environment. The whole coil is axially placed inside the two poles with carbon brushes and slip rings facilitating the field current. Two fans are used at rear ends of the poles to ensure the thermal stability of the generator. The AC voltage is further converted to DC using silicon diode bridge rectifiers. To avoid ripple factor, a three stage coiling is done to ensure leakage. Moreover, in order to establish a steady flow of current at the output, Voltage regulators are available at the battery terminals in automotive alternators.
The necessity of constant voltage is where the theory of field current comes into play. Although old models had a separate voltage regulator, the recent models incorporate the regulator inside the ‘Compact Alternator’ to minimize the space. Heavy weight trucks and load vehicles require space to remain stable when the engine revs. The ability of an AC Generators to produce requisite amount of electricity is directly proportional to the number of turns in the coils and the change in magnetic flux of the coil. One can increase and decrease the efficiency of generator if you know its proper application. The need of an AC generator was felt inevitable after the Dynamo failed to generate enough electrical energy to encompass proper functioning of the head lights, wipers and heated rear windows. It is a quintessential part of our day-to-day automobile technology.