frame and laminated to reduce eddy current losses and serve the same purpose as the iron core of an electromagnet; they  concentrate the lines of force produced by the field coils.  The field coils are made up of many turns of insulated wire  and are usually wound on a form that fits over the iron core  of the pole to which it is securely fastened.  [Figure 9-46] The frame has two functions: to hold the windings needed to  produce a magnetic field, and to act as a mechanical support  for the other parts of the generator. The actual electromagnet  conductor is wrapped around pieces of laminated metal called  field poles. The poles are typically bolted to the inside of the  The major parts, or assemblies, of a DC generator are a field  frame, a rotating armature, and a brush assembly. The parts  of a typical aircraft generator are shown in  Figure 9-45 . Construction Features of DC Generators Field Frame Figure 9-41.  Generator slip rings and loop rotate; brushes are  stationary.  Figure 9-40.  Output of an elementary generator. Figure 9-42.  A two-piece slip ring, or commutator, allows brushes to transfer current that flows in a single direction (DC). 9-29 Figure 9-39.  Battery troubleshooting guide (continued). N S B A – Voltage + Voltage Maximum Minimum 0° Maximum 90° 270° 360° 1 cycle 180° Induced EMF 1 Revolution A E B C D Trouble Probable Cause Corrective Action Distortion of battery case and/or cover Explosion caused by: Dry cells Charger failure High charge voltage Plugged vent caps Loose intercell connectors Discharge battery and disassemble.  Replace damaged parts and  recondition. Discolored or burned end connectors  or intercell connectors Dirty connections Loose connection Improper mating of parts Clean parts: replace if necessary.  Retighten hardware using proper  torque values. Check to see that parts  are properly mated.