Lesson 1/Learning Event 1
As you can see, to induce electricity in a conductor, we must have a magnetic field and motion. In
automotive generators, mechanical energy from the engine is used to supply the motion. On some
types of generators, the conductor is moved through a stationary magnetic field, while on others the
magnetic field is moved and the conductor is stationary.
The induction principle is also used in TRANSFORMERS. A transformer is an electrical device
that is used for stepping up or stepping down electrical voltage. The ignition coil of an automotive
vehicle is actually a transformer that steps the 12- to 24-volt battery voltage up to the several
thousand volts needed to ignite the fuel mixture. In the following paragraphs, we will discuss the
construction and operation of transformers.
A simple transformer often contains an iron core and consists of two coils of wire. One coil is
actually an electromagnet and is called the primary winding. The second coil is called the
If the primary winding is connected to a battery, current will flow through the winding causing a
magnetic field to build up around the coil. As the field builds up, its lines of force move outward
cutting across the coils of the secondary winding. The secondary winding will have a voltage
induced in it as a result of the lines of force cutting across its coils. Now, if the ends of the
secondary winding conductor were connected into a complete circuit, current would flow until the
induced voltage dropped to zero.
When the primary winding is disconnected from the battery, the magnetic lines of force will
collapse and disappear. As this happens, the lines of force move rapidly inward toward the primary
winding. Again, the moving lines of force cut across the coils of the secondary winding inducing a
voltage. This time the lines are moving in the opposite direction so the induced voltage causes
current to flow in the opposite direction.