Certain of the foregoing and related objects are readily attained in a brushless alternator having a three-phase stator winding, consisting of at least one set of delta connected stator coils disposed in stator plates and surrounding the main field winding in the rotor. The rotor is disposed on a shaft rotatably supported within the housing of the alternator. An exciter and shaft-mounted rectifying means are provided for supplying DC voltage to the main winding of the rotor. The exciter field coil is wound spool-like on a core, with the field coil contained within an exciter stator attached to the alternator housing. The main winding in the rotor is wound spool-like on a core with the rotor having a cylindrical sleeve extending from one end and engaging and supporting the exciter armature in alignment with the exciter stator.

The exciter produces a three-phase AC voltage which is rectified by diodes mounted to and rotating with the alternator shaft. The rectified voltage is supplied to a main field winding disposed within the rotor mounted onto the shaft. This, in turn, provides a DC current flow in the main field winding, which is required for inducing the ac alternator output current, in a main armature winding. The exciter and main field windings are wrapped sequentially and annularly around their respective cores. The exciter armature is attached to and partially enclosed within a cylindrical flange extending outward from the rotor. The exciter field coil is disposed within and surrounded on its sides by the exciter armature.

A feedback circuit is provided within the ac generator in order to maintain output voltage during varying load and temperature conditions. Within the stator is a set of feedback coils in a three-phase delta connection. The output voltage from these coils is rectified and supplied to a voltage regulator, as shown in FIG. 3. When the battery voltage deviates beyond the working range, the voltage regulator compensates by supplying a correspondingly higher or lower DC voltage to the field coil in the exciter stator, as required. This, in turn, results in the desired change of output voltage.

An alternator is an electromechanical device that converts mechanical energy to alternating current electrical energy. Most alternators use a rotating magnetic field but linear alternators are occasionally used. In principle, any AC generator can be called an alternator, but usually the word refers to small rotating machines driven by automotive and other internal combustion engines. Alternators in power stations driven by steam turbines are called turbo-alternators.

Alternating current generating systems were known in simple forms from the discovery of the magnetic induction of electric current. The early machines were developed by pioneers such as Michael Faraday and Hippolyte Pixii.

Faraday developed the "rotating rectangle", whose operation was heteropolar - each active conductor passed successively through regions where the magnetic field was in opposite directions. The first public demonstration of a more robust "alternator system" took place in 1886. Large two-phase alternating current generators were built by a British electrician, J.E.H. Gordon, in 1882. Lord Kelvin and Sebastian Ferranti also developed early alternators, producing frequencies between 100 and 300 Hz. In 1891, Nikola Tesla patented a practical "high-frequency" alternator (which operated around 15 kHz). After 1891, polyphase alternators were introduced to supply currents of multiple differing phases. Later alternators were designed for varying alternating-current frequencies between sixteen and about one hundred hertz, for use with arc lighting, incandescent lighting and electric motors.

Construction

A brushless alternator is composed of two alternators built end-to-end on one shaft. Smaller brushless alternators may look like one unit but the two parts are readily identifiable on the large versions. The larger of the two sections is the main alternator and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier, called the rotating rectifier assembly, is mounted on a plate attached to the rotor. Neither brushes nor slip rings are used, which reduces the number of wear parts.

 Main alternator

The main ac alternator has a rotating field as described above and a stationary armature (power generation windings).

 Control system

Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.

 Automatic voltage regulator (AVR)

The AVR regulates the alternator's output voltage by varying the amount of current in the stationary exciter field coils. Automatic voltage control may be used where load current variations exceed the built-in ability of the generator to regulate itself. An automatic voltage control device "senses" changes in output voltage and causes a change in field resistance to keep output voltage constant.