The secondary winding consists of thousands of turns of smaller wire, insulated from the high voltage by enamel on the wires and layers of oiled paper insulation. The primary winding has relatively few turns of heavy wire. The energy that is stored in the magnetic field of the core is the energy that is transferred to the spark plug.
Unlike a power transformer, an ignition coil has an open magnetic circuit - the iron core does not form a closed loop around the windings. Ignition systems are not required for diesel engines which rely on compression to ignite the fuel/air mixture.Īn ignition coil consists of a laminated iron core surrounded by two coils of copper wire. A modern passenger automobile may use one ignition coil for each engine cylinder (or pair of cylinders), eliminating fault-prone spark plug cables and a distributor to route the high voltage pulses. More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil. Originally, every ignition coil system required mechanical contact breaker points and a capacitor (condenser). The wire that goes from the ignition coil to the distributor and the high voltage wires that go from the distributor to each of the spark plugs are called spark plug wires or high tension leads. Some coils have an internal resistor, while others rely on a resistor wire or an external resistor to limit the current flowing into the coil from the car's 12-volt supply. Dual ignition coils (blue cylinders, top of picture) on a Saab 92.Īn ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel.
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