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 TM 9-8000
CHAPTER 13
CHARGING SYSTEMS
Section I PRINCIPLES OF OPERATION
a. More Current Induced. In the simple, single-loop
13-1. General. The generator is a machine in which the
generator (fig. 13-1), the current produced in each side
principle of electromagnetic induction is used to convert
of the loop reaches a maximum when the sides are
mechanical energy into electrical energy. The generator
cutting the lines of force in a perpendicular direction.
restores the current used in cranking the engine to the
This is the position in which the loop is shown. As the
battery. It also supplies, up to the limit of its capacity,
loop moves away from this position, it cuts fewer and
current to carry the electrical load of the lights, ignition,
fewer lines of force and less and less current is
radio, and horn. A generator and a motor are basically
produced. By the time the loop has turned 90 degrees
the same in construction and use the same electrical
from the position shown, the sides are moving parallel to
principles; however, their operation is opposite. In the
the lines of force and are cutting no lines, therefore no
generator, mechanical motion is converted into electrical
current is being produced. The current produced from
energy. In the motor, electrical energy is converted into
the single loop is shown in graph form in figure 13-1.
mechanical motion.
Many loops, or turns, of wire are required in the
13-2. Simple Single-Loop Generator.
conductor in order for the generator to produce an
a.
Induced Current. If a single loop of wire is
appreciable amount and even flow of current. The
rotated in the magnetic field between a north and a south
rotating member that contains the wire loops and the
pole, there will be an electrical pressure produced in the
commutator is called an armature. Figure 13-2 shows
two sides of the loop. The voltage and current produced
an armature in place in a generator. Note that many
will relate to the direction of the magnetic field and the
turns are used in the armature windings.
direction of rotation. If each end of the loop is connected
b.
Smoother Current Flow.
The windings are
to a metal segment of a commutator on which brushes
assembled in a soft iron core because iron is more
rest (fig. 13-1), this electrical pressure will cause a
permeable than other substances that could be used.
current to flow through any external circuit that may be
The windings are connected to each other and to the
connected across the two brushes.
commutator segments in such a way that the current
b.
Commutation. If the loop is rotated through a
impulses overlap and produce a smooth flow of current.
complete revolution (fig. 13-1), sides 1 and 2 will cut
This could be compared to the overlapping of power
magnetic lines of force in first one direction and then in
impulses in an 8- or 12-cylinderenglne.
the other. This will produce current in each side of the
loop, first in one direction and then in the other. That is,
in side 1, current will flow in one direction when it is
provide rated output, it must be operated at sufficient
passing the north pole and in the other direction when it
speed. Because military vehicles spend a large amount
is passing the south pole. However, because the
of time at engine idle, it is important to note that during
commutator segments also rotate with the loop, the
these periods the generator may be required to supply
current always will leave the right-hand brush (4) and
full rated current on a large portion thereof. Therefore,
enter the left-hand brush (3). The directions of current
the requirement for establishing the speed at which full
produced in each side of the loop can be determined by
rated output must be delivered is the controlling factor for
use of the left-handed rule, described in paragraph 11-
optimizing the size of the generator. As a general rule,
14.
engines have a speed ratio between four and five to one
from idle to maximum speed; that is, the typical engine
13-3. Multiple-Loop Generator. The advantages of a
idles at 650 rpm and has a maximum speed of 3,000
multiple-loop
generator
are
explained
below.
rpm. Typical
13-1
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