Ignition coils are used to ‘step up' the voltage of the engines primary circuit of the 12 – 24 volt range to 20,000 to 40,000 volt range. The increased voltage is required for the current to jump the spark gap in spark plugs, producing the ignition of the air/fuel mixture. The increase of the voltage is matched by a proportionate decrease in current.
At its most basic an ignition coil is made up of a primary winding, a secondary winding and a laminated core.
The secondary winding is wound with considerably more turns than the primary winding. The resulting difference in number of turns is proportional to the ‘step up' in voltage. An inductive ignition system will charge the primary winding with generally 12 volts, when the current is removed a large EMF is generated in the secondary winding of up to 40,000 Volts, more than enough to jump across a spark gap.
In practice ignition coils will have some extra components but are in operation practically the same.
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Introduction to Ignition Coils
