B C D E 0 1/4 1/2 3/4 1 Induced EMF Revolutions (B) S N Figure 9-44.  Typical DC generator commutator. Figure 9-43.  Increasing the number of coils reduces the ripple in  the voltage. A DC current is fed to the fi eld coils to produce an  electromagnetic field. This c urre nt is typically obtained  from an external source that  provides voltage and current  regulation for the generator system. Generator control  systems are discussed later in this chapter.  The armature assembly of a generator consists of two primary  elements: the wire coils (called windings) wound around  an iron core and the commutator assembly. The armature  windings are evenly spaced around the armature and mounted  on a steel shaft. The armature rotates inside the magnetic field  produced by the field coils. The core of the armature acts as  an iron conductor in the magnetic field and, for this reason,  is laminated to prevent the circulation of eddy currents. A  typical armature assembly is shown in  Figure 9-47 . Armature Connector lugs Field frame Drive end frame Sealed ball bearings Drive shaft Field winding Screw Pole shoe Brush and holder Steel ring Commutator Brush connector bars Air scoop Armature Drive end Field frame Commutator end frame Figure 9-45.  Typical 24-volt aircraft generator. 9-30$^{A}$