A B C 90° 180° 270° 360° 120° 120° 120° Phase C Phase A Phase B One full rotation of the AC alternator Phase 1 Phase 2 Phase 3 Figure 9-66.  Sine waves. Figure 9-64.  DC alternator installation. Figure 9-67.  Three-phase armature windings: Y on the left and  delta winding on the right. Figure 9-68.  Relatively smooth ripple DC.  Figure 9-65.  Diagram of a typical alternator. To electrical load + − Rectifier assembly Armature winding Field 1 2 3 Time Resultant DC waveform 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.  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. 9-39