Induction coils were originally developed in 1836 and were previously known as Ruhmkorff coils, although they were actually invented by a man named Nicholas Callan.
The term induction refers to the act of generating electromotive force in a closed circuit by means of a change in the current flow. Ignition coils and induction coils share the nickname of “spark coils”, since an ignition coil is a type of induction coil.
Having been around the longest of currently-in-use electrical coils, induction coils are widely utilized in diverse industries including: medical, for imaging equipment such as x-ray machines; electronics, for equipment such as wireless radio transmitters, telephone circuits, cameras and strobe lights, automotive, for use in ignition systems for vehicles featuring internal combustion engines such as cars, trucks and vans; agriculture, for farming machinery such as balers, combines and tractors; and industrial manufacturing, for use in powering parts and equipment such as vacuum tubes.
Induction coils consist of four main parts: a ferromagnetic core, a primary coil, a secondary coil and an interrupter. The ferromagnetic core is typically manufactured from solid iron, solid steel or powdered iron, although solid iron is probably the most popular of the three materials. The primary coil is a heavy gauge of conductive metal wire, commonly copper, that is wound around the core a small number of times (the winding is referred to as turns).
The primary coil is attached to the low-voltage DC power supply. The secondary coil is a finer gauge of the same conductive metal wire, and instead of being wound directly around the core, the secondary coil is wound over the primary coil. The secondary coil, as it is made from a finer gauge, consists of many more turns than that of the primary coil.
The secondary coil is not attached to the DC power supply, but is instead attached to whatever requires powering, serving as a high-voltage output of AC current flow. An interrupter, also referred to as a break, is a magnetically-activated vibrating arm. The interrupter functions within the inductor coil to ensure a quick connection as well as break-up of the current flowing into the primary coil. The interrupter is typically mounted on the end of the induction coil, close to the core.