Understanding Ignition Coils

Engine Ignition Coil

Ignition coils, also known as spark coils are an induction coil in an automobile’s ignition system. It transforms a storage battery’s 12 volts to the thousands of volts needed to spark the spark plugs.

This particular form of the autotransformer (an electrical transformer with only one winding and it has three electrical connection points called taps), together with the contact breaker (a type of switch found in the distributor of the ignition systems of non-diesel powered internal combustion engines) will convert the low voltage from the battery into the high voltage that is required by the spark plugs in an internal combustion engine. The purpose of the contact breaker is to interrupt the current flowing in the primary circuit of the ignition coil.

In modern ignition systems, there is no ignition distributor and ignition is electronically controlled instead, and firing voltage is then achieved by one of the following ways:

  • Coil on plug
  • Waste spark

In the coil on plug system, each spark plug will have its own individual coil that sits right on top of it. This is a Direct Ignition module.

Ignition Coil Types

Ignition Coil Types
Ignition Coil Types

In a waste spark system, the two spark plugs will share the same coil. So, therefore, in this system, both spark plugs are attached to the coil and are fired simultaneously. 

Even though the spark plugs are manufactured exactly the same, if they are re-installed after there has been some extended use, they should then go back into the cylinder from which they came from. The reason for this is because the electrons will align themselves favorably with one direction of current flow.

Ignition System Wiring Diagram

While one plug will receive positive potential (voltage) at the wire side, the piston pair will receive the negative potential. The negative potential is what causes the second plug to fire. Vehicles seem to use the conventional theory as opposed to the electron theory of current flow.

The waste spark system is better than having a single coil. It is also cheaper than having a coil on the plug. The disruptive discharge Tesla coil is an earlier coil of the ignition coil in the ignition system. It also uses the same principles of the ignition coil that is in today’s vehicles.

Ignition Systems Engineering Explained