An induction coil is a type of electrical transformer that uses a low-voltage DC supply to produce high-voltage pulses. The coil is made up of two coils made up of insulating copper wire wound around a common iron core. The first coil is small, usually made up of tens or hundreds of turns of coarse wire. This is known as the primary winding. The second coil, known as the secondary winding, is made up of thousands of turns of fine wire.
The coil works by sending a small electric current through the primary coil. This creates a magnetic field. Since both primary and secondary windings are wrapped around a common iron core, the primary winding is coupled with the secondary winding. When the voltage going into the primary is suddenly interrupted or stopped, the magnetic field collapses quickly.
The sudden collapse of the magnetic field creates a high voltage pulse to be developed across the terminals connected to the secondary windings, by a process known as electromagnetic induction. Since the secondary coil has thousands of turns of wire, the pulse created is in thousands of volts. In most cases, when the pulse is created in the secondary coil, it creates a spark or jump between terminals. This is why the induction coil is often referred to as the “spark coil.”
In order to get the induction coil to work, the electrical current that is fed to the primary coil has to be interrupted on a continuous basis. The device that causes the interruption is known as an interrupter. The interrupter that connects and breaks the current to the primary winding is made of a vibrating mechanical contact.
When a magnetic field is created in the primary winding, this field attracts or pulls an iron armature that is attached to a spring. This pulling of the iron armature breaks a pair of contacts that connect to a power source. Once the power source is broken, the magnetic field collapses, resulting in the spring closing the contacts. When the contacts close, the cycle starts over again.
Induction coils are used quite often in television sets and other electronic devices where low-voltage needs to be converted to high-voltage. A car's ignition system uses an induction coil to convert power from the battery. Induction heating is the use of an induction coil to provide localized, controlled heat objects placed inside the coil.