Figure 15-23. Magneto Generator.
provides mechanical energy for motion between the field
the ratio of the number of turns on the primary winding to
and the conductor. There are two types of magnetos:
the number on the secondary winding. This makes
armature-wound, in which the coil moves while the
about 15,000 volts available at the spark gap.
magnets are stationary; and the inductor type, in which
the reverse is true, the magnets move and the coil is
15-12. Interrupting Device (Fig. 15-22).
stationary. In the inductor type, for example, a rotor that
is a permanent magnet is used to direct the magnetic
a. Breaker Points. The interrupting device, which
field flow through the windings, first in one direction and
breaks the primary circuit when the high voltage spark is
then in the other. Because the winding is stationary, it is
desired, is a set of breaker points. One end of the
easier to make connections from it. Either type of
primary winding is connected to a ground; the other to
construction satisfies the first requirement of an electric
the insulated breaker point. When the points are closed,
Ignition system, that Is, a means of developing electrical
the circuit is completed through them to a ground; when
open, the circuit is broken. Lobes on a cam actuate the
breaker points, Interrupting the primary circuit and timing
15-11. Transforming Device (Fig.
the Induction of maximum voltage in the secondary
engines require about 15,000 volts at the spark gap in
circuit. The cam Is mounted on either the armature or
the cylinder. The problem when the magneto is used is
to raise the low voltage induced in the conductor (primary
winding) to the required high voltage.
b. Capacitor. When the breaker points are opened,
accomplished in the same way that it is in the battery
the current then flowing in the primary circuit tends to arc
ignition coil. When the current in the primary winding or
across the points due to self induction. This reduces the
conductor is at its maximum flow, the circuit Is broken
speed with which the circuit is broken and the magnetic
suddenly, collapsing the electromagnetic field set up
field collapses. This action is controlled by inserting a
around the primary circuit as the result of current flow.
capacitor In parallel with the breaker points. When the
The lines of force In the field collapse at an extremely
primary circuit is broken, the capacitor receives the surge
high rate of speed across the secondary winding, which
of current and then, on discharging, reverses the normal
is made up of many turns of fine wire, whereas the
flow of current. The capacitor thus hastens the collapse
primary winding is composed of relatively few turns of
of the magnetic field around the primary winding and
coarser wire. This rapid movement of the lines of force
Increases the amount of voltage induced.
across the secondary winding induces a momentarily
high voltage in the secondary winding, in proportion to