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What is an Alternator

What does an Alternator so in an Car or Truck?

Contributed By: Chris M.

An alternator is an engine part that transforms moving energy into electric energy in the form of a changing current. Typically, an alternator uses a rotating magnetic field with a non-moving armature. However, occasionally, a revolving armature is used with a non-moving magnetic field; Else, a linear alternator is used. In general, any A/C electric generator can be considered an alternator, but, typically, the term refers to tiny rotating machines driven by automotive and miscellaneous internal combustion engines. Alternators that use an everlasting magnet for its magnetic field are considered magnetos.

Alternators within power stations that are driven by steam turbines are considered turbo-alternators. Alternating current generating systems were simplified by the discovery of the magnetic induction of electric current. These early machines were developed by scientific pioneers such as Michael Faraday and Hippolyta Pixii.

Faraday developed the "rotating rectangle", whose function was heteropolar; that is, each active conductor passed through regions where the magnetic field was moving in opposite directions. Alternators create electricity by using the same principle as DC generators, explicitly, when the magnetic field surrounding a conductor changes, a current is induced within the conductor. Usually, a revolving magnet called the rotor turns within a placed set of conductors wound in coils around an iron core, which is called the stator. This field cuts across conductors, which creates an induced emf (electromotive force) as the moving input forces the rotor to turn. The revolving magnetic field induces an AC voltage within the stator windings. Usually, there are three groups of stator windings, which are intentionally offset so that the revolving magnetic field produces a three phase current, which is moved by one-third of a period with respect to one another. The rotor's magnetic field could be produced by induction (i.e. a "brushless" alternator) by everlasting magnets (i.e. miniscule machines), or by a rotor winding energized with straight current through slip rings and brushes. The rotor's magnetic field could be provided by non-moving field winding, with mechanic poles in the rotor.

Automotive alternators invariably use a rotor winding, which allows jurisdiction of the alternator's generated voltage shifting the current in the rotor field winding. Everlasting magnet machines avoid the loss because of a magnetizing current in the rotor, which are restricted in size because of the cost of the magnet material. Because the everlasting magnet field is constant, the final voltage varies directly with the velocity of the generator.

Brushless AC generators are typically bigger machines than those that are used in automotive applications. An automatic voltage control device jurisdictions the field current to keep output voltage invariable. If the output voltage from the placed armature coils decreases due to amplification in demand, more current is fed into the revolving field coils throughout the voltage regulator (VR). This enlarges the magnetic field surrounding the field coils which induces a bigger voltage in the armature coils. Hence, the output voltage is brought back into its initial value. Alternators are commonly used in modern automobiles to charge batteries and to power the electric system when the engine is running. Until the 1970s arrived, automobiles typically used DC dynamo generators with commutators. With the accessibility of affordable silicon diode rectifiers, alternators were used.

Alternators have numerous advantages over DC generators. They weigh less, they are cheaper, and they are more rugged. They tend to use slip rings providing incredibly extended brush life over a commutator. These brushes within an alternator only carry excitation current, which is a tiny fraction of the current that is carried by the brushes of a DC generator, which carry the entire generator's output. A group of rectifiers (diode bridges) is required to transform AC to DC. To allow direct current with a low ripple, a three-phase winding is typically used and the pole-pieces of the rotor are shaped (claw-pole) differently to produce a form similar to a square wave instead of a sinusoid (which is a sine or cosine wave). Automotive alternators are typically belt driven at two to three times crankshaft speed. The alternator runs at variable RPM (which distorts the frequency) because it is driven by the engine. Apparently, this is not an issue since the alternating current is rectified to direct current.

We hope this article gives you a general idea of what an alternator is and the basics of what the alternator does in your vehicle.

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