An ignition coil (also called a spark coil) is an induction coil in an automobile 's ignition system which transforms the battery's low voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel.uch smaller coils are used with one coil for each spark plug or one coil serving two spark plugs (for example two coils in a four-cylinder engine, or three coils in a six-cylinder engine). A large ignition coil puts out about 40 kV, and a small one such as from a lawn mower puts out about 15 kV.