Lesson3/Learning Event 1
How much voltage will be induced into the primary and secondary windings by the collapsing
magnetic field? Well, that will depend on the speed with which the field collapses (speed of the
motion) and the number of turns of wire in each coil. The more turns of wire in the windings, the
greater the induced voltage will be. In the primary winding of most automotive coils, there are a
few hundred turns of wire and the voltage induced will be about 200 or 250 volts. Because the
primary circuit is now open (that is why the magnetic field collapsed), this voltage is not going
anywhere except into the capacitor, which we will study later. While the magnetic field is
collapsing across the few hundred turns of primary winding, it is also moving across the thousands
of turns of secondary winding. Voltage induced into each turn of each winding is about the same.
Since the secondary winding has many more turns, the total voltage induced into it will be in the
thousands of volts. This voltage is high enough to force current to flow out of the coil, through
the secondary terminal, and through the conductors to the spark plug in the cylinder. There the
current is forced, by the high voltage, to jump the air gap and ignite the fuel mixture. This current
then returns to its source, in this case the secondary winding of the coil.
IGNITION DISTRIBUTOR
We stated earlier in this lesson that the ignition distributor has two separate and distinct jobs to do.
One job involved the primary circuit, while the other job was concerned with the secondary circuit.
Let us discuss the primary circuit first. The parts we will discuss are the distributor breaker points,
distributor cam, and the capacitor (condenser).
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