Ignition Coils: Dead, Deader, Deadest

V = A x Ω is a formula familiar to anyone who's done a little electrical work: Voltage = Current X Resistance.

In spark ignition (gasoline) engines, this formula is an important one: to take our fixed amount of current from the battery/alternator and overcome the high resistance of the spark plug's air gap, we need a lot of voltage to make a spark that'll jump the gap. This is where ignition coils come to the rescue.

Essentially miniature transformers, ignition coils use a high current primary (input) winding of thick copper wire and a high voltage secondary (output) winding of many loops of thin copper wire, all wrapped around an iron core:

1. Electricity flows through the input winding's coils of wire
2. The electricity traveling along the multiple loops of the input coil winding makes a magnetic field
3. The loops of the output winding capture the magnetic field and turn it back in to electricity

The ratio of output winding to input winding coils determines voltage, so ignition coils typically have hundreds of input winding coils but thousands of output winding coils to step up the voltage to a high enough level to make a strong spark. A usual ignition system voltage might be anywhere from 20000 to 40000 volts, with greater voltage needed to keep the spark from blowing out in high compression or high boost engines.