Ignition Coil: Description and Operation

Fig. 103 Ignition Coil:

Construction
The ignition coil, Fig. 103, consists of a metal housing which accommodates metal plate jackets for reducing stray magnetic fields. The secondary winding is wound directly onto the laminated iron core and connected electrically to the center tower in the cap of the ignition coil via the core. Since the high tension is applied the iron core, the core must be insulated by the cap and an additional insulator inserted in the base.

The primary winding is located near to the outside around the secondary winding. The insulated ignition cap contains the terminals for the battery voltage and the connection to the contact breaker, symmetrically with the high tension tower. The windings are insulated and mechanically locked in position by potting with asphalt. Oil filled ignition coils are also available. The heat is dissipated through the metal plate jackets to the can.

Fig. 77 Charging the Ignition Coil:

Coil Saturation
The rotor slots shield the Hall effect switch from the magnetic field, preventing voltage generation by the Hall switch, Fig. 77. The output module is energized, thereby closing the primary circuit, and the primary winding becomes saturated with voltage.

Fig. 78 Discharging the Ignition Coil:

Spark Generation
When the rotor shield moves clear of the Hall effect switch, a voltage is generated, Fig. 78. This voltage is sensed by the control unit, which opens the primary circuit. The magnetic field in the coil collapses, thereby generating a voltage in the secondary coil, and a spark is generated.