The charging system provides the electrical energy required by the various electrical systems and also keeps the battery charged. Types of charging systems
This was the type of electrical generator used on older vehicles. It consisted of a rotating conductor inside a fixed magnetic field. Rectification of the A.C. current to D.C. was by means of a commuter. Output of the dynamo was limited due to the rotating speed of the conductor 2. Alternator
In the alternator the magnetic field rotates, while the conductor is stationary. This allows the alternator to operate at higher speeds than the dynamo, giving greater output. Generating an electric current
The simple dynamo
When a coil of conducting wire is rotated between two magnets an E.M.F is produced and will cause an alternating current to flow in the wire. Waveforms
As the conductor rotates between the magnets the E.M.F. will vary. This can be shown in the form of a sine wave, which will show the peak voltage and the zero voltage. One complete turn of the conductor is called a cycle. The number of complete cycles that occur in one second is called the frequency (Hertz). The frequency of a generator depends upon its speed For many applications including battery charging the A.C. must be converted to D.C. This is achieved when the negative half-wave is transferred to the positive and is called full-wave rectification. Principle of operation of the alternator
In a basic alternator a shaft containing a four pole magnet, rotates inside a stationary stator. The stator has a conductor coil wound around it. Rotation of the magnet generates an E.M.F. in the stator windings. Because the north and south poles of the magnet pass the stator in alternate order, the current produced will be A.C. Output increases as the speed increases until a point is reached where self-inductance will retard any further current increase. This protects the alternator against current overload. In...