IGNITION COIL (or Induction Coil)
The ignition coil is simply a transformer to step up the voltage in the ignition system. It consists of a soft iron core, primary winding, and secondary winding. The primary winding consists of 200-300 tums of thick wire (20 SWG) and the secondary winding 15,000-20,000 turns of fine wire (40 SWG). The core is formed by the lamination of soft iron.
The ignition coils may be of two types:
1.Core type ignition coil
In this type of coil, the primary winding is wound around the iron core forming double C with air gaps. The secondary winding is wound outside the primary winding. The core is of rectangular cross-section and is made of soft iron lamination.
2.Can type ignition coil
In this type of coil, the secondary winding is wound around the core, and then the primary winding is wound over the secondary winding. The core assembly is placed in a steel casing that is fitted with a cap of molded insulating materials. The terminals are provided in the cap. The windings are immersed in oil to improve insulation and to reduce moisture effect.
hen the ignition switch is turned on, the current flows from the battery through the primary winding. When the contact breaker points open, the primary circuit breaks and the magnetic field collapses. Rapid collapsing of the magnetic field induces a high voltage in both the primary and secondary winding.
The current flowing in the primary winding runs towards contact breaker points and is observed by the condenser placed across them, and the circuit is completed through the earth. The high voltage current flowing through the secondary winding goes to the distributor from where it is distributed to the proper spark plug through the high tension lead, where it jumps the spark plug gap producing the spark.
How does an Ignition Coil work?
Materials of Ignition Coil
Early, ignition coils are made with paper and varnish insulated high-voltage windings, inserted into a steel can and filled with oil or asphalt for insulation and moisture protection. Coils on modern automobiles are cast in filled epoxy resins that penetrate any voids within the winding. A modern single-spark ignition system has one coil per spark plug. To prevent premature sparking at the start of the primary pulse, the diode or secondary spark gap is used in the coil to block the reverse pulse that would otherwise form.
In the coil meant for a dual-spark system, the secondary winding has 2 terminals isolated from the primary, and each terminal connects to the spark plug. With this system, no extra number of diodes are needed since there would be no fuel-air mixture present at the inactive spark plug. In a low-inductance coil, fewer primary tuns are used, so the primary current is higher. This is not compatible with the capacity of mechanical breaker points, so solid-state switching is used.