Ignition coil

Modern car engines often use a distributor-less system (such as coil-on-plug), whereby every cylinder has its own ignition coil.

When the electrical circuit connected from the power source (e.g. the car's battery) to the primary winding is closed (by a contact breaker or transistor), current flows through the primary winding, which produces a magnetic field around the core.

Once the coil is charged, the circuit is opened, and the resulting oscillation in the magnetic field induces a high voltage in the secondary winding.

[citation needed] A modern single-spark system has one coil per spark plug.

], ignition coils were instead cast in filled epoxy resins, which penetrate any voids forming within the windings.

An advantage of coil-on-plug systems is that in the event of a fault, a single ignition coil can be replaced rather than, unnecessarily, those for all of the cylinders.