exert excessive pressure that may cause the battery to  buckle causing internal shorting of the battery. the generator loop into a DC voltage. The action of the  commutator allows the generator to produce a DC output. By replacing the slip rings of the basic AC generator with  two half cylinders (the commutator), a basic DC generator is  obtained. In  Figure 9-42 , the red side of the coil is connected  to the red segment and the amber side of the coil to the amber  segment. The segments are insulated from each other. The  two stationary brushes are placed on opposite sides of the  commutator and are so mounted that each brush contacts  each segment of the commutator as the commutator revolves  simultaneously with the loop. The rotating parts of a DC  generator (coil and commutator) are called an armature. As seen in the very simple generator of  Figure 9-42 , as the  loop rotates the brushes make contact with different segments  of the commutator. In positions A, C, and E, the brushes touch  the insulation between the brushes; when the loop is in these  positions, no voltage is being produced. In position B, the  positive brush touches the red side of the conductor loop. In  position D, the positive brush touches the amber side of the  armature conductor. This type of connection reversal changes  the AC produced in the conductor coil into DC to power the  aircraft. An actual DC generator is more complex, having  several loops of wire and commutator segments.  DC generators transform mechanical energy into electrical  energy. As the name implies, DC generators produce direct  current and are typically found on light aircraft. In many  cases, DC generators have been replaced with DC alternators.  Both devices produce electrical energy to power the aircraft’s  electrical loads and charge the aircraft’s battery. Even though  they share the same purpose, the DC alternator and DC  generator are very different. DC generators require a control  circuit in order to ensure the generator maintains the correct  voltage and current for the current electrical conditions of  the aircraft. Typically, aircraft generators maintain a nominal  output voltage of approximately 14 volts or 28 volts. Because of this switching of commutator elements, the  red brush is always in contact with the coil side moving  downward, and the amber brush is always in contact with  the coil side moving upward. Though the current actually  reverses its direction in the loop in exactly the same way as  in the AC generator, commutator action causes the current  to flow always in the same direction through the external  circuit or meter.  The voltage generated by the basic DC generator in  Figure 9-42  varies from zero to its maximum value twice  for each revolution of the loop. This variation of DC voltage  is called ripple and may be reduced by using more loops, or  coils, as shown in  Figure 9-43 .  As the number of loops is increased, the variation between  maximum and minimum values of voltage is reduced  [Figure 9-43] , and the output voltage of the generator  approaches a steady DC value. For each additional loop in  the rotor, another two commutator segments is required. A  photo of a typical DC generator commutator is shown in  Figure 9-44 . Since the conductor loop is constantly rotating, some means  must be provided to connect this loop of wire to the electrical  loads. As shown in  Figure 9-41,  slip rings and brushes can  be used to transfer the electrical energy from the rotating  loop to the stationary aircraft loads. The slip rings are  connected to the loop and rotate; the brushes are stationary  and allow a current path to the electrical loads. The slip  rings are typically a copper material and the brushes are a  soft carbon substance.  The principles of electromagnetic induction were discussed  earlier in this chapter. These principles show that voltage is  induced in the armature of a generator throughout the entire  360° rotation of the conductor. The armature is the rotating  portion of a DC generator. As shown, the voltage being  induced is AC.  [Figure 9-40] It is important to remember that the voltage being produced  by this basic generator is AC, and AC voltage is supplied  to the slip rings. Since the goal is to supply DC loads, some  means must be provided to change the AC voltage to a DC  voltage. Generators use a modified slip ring arrangement,  known as a commutator, to change the AC produced in  9-27 •  Quick-disconnect type battery—If a quick-disconnect  type of battery connector that prohibits crossing the  battery lead is not employed, ensure that the aircraft  wiring is connected to the proper battery terminal.  Reverse polarity in an electrical system can seriously  damage a battery and other electrical components.  Ensure that the battery cable connections are tight to  prevent arcing or a high resistance connection. See  Figure 9-39  for a troubleshooting chart. Troubleshooting DC Generators and Controls  Generators