Lesson3/Learning Event 2
Learning Event 2:
DESCRIBE THE CONSTRUCTION AND OPERATION OF IGNITION SYSTEM
The ignition coil is really a step-up transformer. You have probably noticed transformers on the
light wire poles near your home. These are usually step-down transformers which change the high
voltage in the transmission wires on the poles to the 110volt current you use in your home. Our
ignition coil does just the reverse of the step-down transformer. It changes the low voltage supplied
by the battery or the generator to the high voltage needed at the spark plugs.
To understand how a coil works, let us review the relationship between electricity and magnetism.
We know that when current flows through a conductor, a magnetic field is created around the
conductor. The strength of the magnetic field depends on the number of loops or coils of wire and
the amount of current flowing through them.
Magnetic fields differ in their flux paths when there is a single, double, or multiple coil of wire
carrying the current.
We can make a magnetic field stronger simply by increasing the number of coils or turns of the
The strength of the magnetic field around the coil can also be increased in two other ways. First, it
can be strengthened by increasing the amount of current flowing in the coil; second, it can be
strengthened by inserting a soft iron core inside the coil of wire. Placing a soft iron core in the
center of the coil will provide an easier path for the magnetic lines of force, or, to put it another
way, the core will increase the number of lines of force because it will reduce the resistance in the
magnetic field. It is much easier for the lines of force to travel through an iron core than through
Now, recall that a magnetic field can induce current into a conductor, provided the conductor is
moved through the field or the field is moved across the conductor. In the case of our coil,
however, as long as direct current flows through the conductor, no current will be induced because
there is no relative movement between the coil and the magnetic field.