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    Hot Rod Tech and Tools Main Page

    Understanding Ignition Coils


    An ignition coil, which is also known as a spark coil is 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 at 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.

    Now days 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 so called Direct Ignition module.

    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 they are fired simultaneously. While one cylinder is toward the end of its compression stroke, its piston pair is nearing the end of the exhaust stroke, and both plugs are then fired.

    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. While the 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 instead of the voltage just going straight to ground after firing the first one. 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, and it is cheaper than having a coil on plug. The disruptive discharge tesla coil is an earlier coil of the ignition coil in the ignition system. It also used the same principles of the ignition coil that is used in today's vehicles.


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