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Ignition Coil (spark coil) is an induction coil which is used to increase the low voltage of the battery – 12 Volt to a very high voltage – about 50000 Volt to produce spark within the engine cylinder for the combustion of fuel. It is used in automobile ignition system. We can also say that it is a short step-up transformer.

Working Principle

Ignition coil or Spark Coil mainly consists of primary winding, a secondary winding, and an iron core. 

When the current Pass through the primary winding, makes and breaks repeatedly by contact breaker, it induces a very high voltage in the secondary winding – about 50000 V. This high voltage from the secondary winding is transferred to the spark plug through ignition distributor to produce spark within the cylinder.

Main Parts

The various main parts of ignition coil are
1. Primary Winding
2. Secondary Winding
3. Iron core

1. primary Winding (coil) – 

It is made up of thick copper wire having 200 to 300 turns insulated from each other

2. Secondary Winding (coil) – 

It is made up of thin copper wire having a large number of turns about 21000 turns. The wires in the secondary winding are insulated from each other by enameled on the wire.

3. iron Core

It consists of a laminated iron core. It is used to store energy in the form of magnetic field.


In ignition coil, the iron core is present at the center, and the primary and secondary windings surround it. The primary winding consists of a thick wire of copper having 200 to 300 turn insulated from each other. On the other hand, the secondary winding is made up of thin copper wire having 2100 turns and insulated from each other by enamel on the wires and layers of oiled paper insulation.


When the ignition switch is ON, the current through the primary winding starts to flow, this creates the magnetic field in the iron core and around it.

As contact breaks in the contact breaker, the primary current collapses. This also collapses the magnetic field in the core. This sudden breaking of the magnetic field induces a very high voltage across the secondary winding. The magnitude of the voltage induced is about 50000 Volt.

This high voltage then is transferred to the spark plug through the ignition distributor to produce a spark for the ignition.


It is mostly used in automobile ignition system and in those vehicles which is run by petrol engines such as scooter, motorcycles, cars etc.It is not used in the vehicles running form diesel engine.

Symptoms Of Ignition Coil Failure

  • Backfiring
  • Starting problems
  • Less fuel economy
  • Engine misfiring
  • Vehicle stalling
  • Engine shaking

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