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## DC Alternators 

DC alternators contain two major components: the armature winding and the field winding. The field winding (which produces a magnetic field) rotates inside the armature and, using the process of electromagnetic induction, the armature produces a voltage. This voltage produced by the armature is fed to the aircraft electrical bus and produces a current to power the electrical loads. Figure 9-65  shows a basic diagram of a typical alternator. 

The armature used in DC alternators actually contains three coils of wire. Each coil receives current as the magnetic field rotates inside the armature. The resulting output voltage consists of three distinct AC sine waves, as shown in Figure 9-66 . The armature winding is known as a three- phase armature, named after the three different voltage waveforms produced. 

Figure 9-67  shows the two common methods used to connect the three phase armature windings: the delta winding and the Y winding. For all practical purposes, the two windings produce the same results in aircraft DC alternators. 

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Since the three-phase voltage produced by the alternators armature is AC, it is not compatible with typical DC electrical loads and must be rectified (changed to DC). Therefore, the armature output current is sent through a rectifier assembly that changes the three-phase AC to DC. [Figure 9-67]  Each phase of the three-phase armature overlaps when rectified, and the output becomes a relatively smooth ripple DC. [Figure 9-68] 

The invention of the diode has made the development of the alternator possible. The rectifier assembly is comprised of six diodes. This rectifier assembly replaces the commutator and brushes found on DC generators and helps to make the alternator more efficient. Figure 9-69  shows the inside of a typical alternator; the armature assembly is located on the outer edges of the alternator and the diodes are mounted to the case. 

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