Cars Simplified: Everything Automotive Explained

Ignition Coil

An ignition coil is a transformer that converts the roughly 13.5 volts[1] available from the vehicle's electrical system and converts it into a very high voltage (about 20,000 to 60,000 volts) that is capable of jumping the spark plug gap. Coils can be designed individually, or as a coil pack.

Ignition coils have a pair of windings inside of them, a primary winding for the primary circuit, and a secondary winding for the secondary circuit. The primary side is supplied voltage from the car (either about 12.6 volts from the car battery during start-up, or about 14 volts from the alternator once it starts working) and is made up of a wire winding wrapped around an iron core.

The secondary windings are also wound around the iron core, but the number of windings from the primary compared to the secondary creates a conversion, based on the number of windings. For example, if the primary side has 100 windings and the secondary side has 500,000 windings, it will convert[2] 12 volts on the primary side into 60,000 volts on the secondary side.

Inside an Ignition Coil by


  1. Although combustion-powered vehicles are known to have 12V batteries and are said to have 12V systems, the runs at a higher voltage, which is needed to recharge the battery.
  2. This assumes an ideal transformer, which allows for easier math and a less complicated understanding of the math.