An ignition coil (also called a spark coil) is an induction coil in a automobile's ignition system which transforms a storage battery's 12 volts to the thousands of volts needed to spark the spark plugs.

This specific form of the autotransformer, together with the contact breaker, converts low voltage from a battery into the high voltage required by spark plugs in a internal combustion engine.

In modern ignition systems each spark plug has its individual coil, sitting right on top of it, in a so called Direct Ignition (DI) module.

The disruptive discharge Tesla coil is an early predecessor of the "ignition coil" in the ignition system. Tesla also gained U.S. Patent 609250, "Electrical Igniter for Gas Engines", on August 16, 1898. It used the principles of the ignition coil used today in automobiles. A. Atwater Kent, in 1921, patented the modern form of the ignition coil.

Related coils

• A Oudin coil is a disruptive discharge coil.

Patents

• U.S. Patent 1391256 - Induction coil structure - Arthur Atwater Kent - 1921
• U.S. Patent 1474152 - Induction coil - Arthur Atwater Kent - 1923
• U.S. Patent 1474597 - Induction coil - Arthur Atwater Kent - 1923
• U.S. Patent 1569756 - Ignition coil - Arthur Atwater Kent - 1926
• U.S. Patent 1723908 - Ignition system - Ernst Alexanderson - 1929