There are two systems of electric ignition:-
1. Battery ignition ( or coil ignition )
2. Magneto ignition
1.Battery or coil ignition system -:
It relates to four cylinder petrol engine it has two circuits, the primary circuit and the secondary circuit. The function of ignition coil is to set-up 6 or 2 volts from the battery to the high tension voltage of about 24,000 volts . Closing the switch, the current from the battery passes through the ammeter , the primary of the induction coil and contact breaker point , the contact pint being closed. The secondary of the induction coil is connected to the distributor arm. The primary winding has a small number of turns of coarse-wire ( between 100 to 200 )whereas a secondary winding has a large number of turns of very fine wire ( of the order of 10,000).
When spark is required in a cylinder, the contact breaker points are opened by the cam and this induces high voltage( the order of 2400 volts ) in secondary. At the same time the distributor arm comes opposite to the point from from where the wire leads to the saprk plug of these cylinder. The high voltage induced in secondary give spark at the spark-plug .
Fig. Battery ignition system
2. Magnet Ignition System-:
In magnet type ignition system , is not required a battery for voltage . It generates its own voltage for the primary. Here an armature having wound upon it in the primary coil of a few hundred turn of enamelled copper wire and secondary coil of several thousand turns of fine insulated wire, rotates in a permanent magnetic field.
In the mordern trend , the armature is to keep stationary and magnets is to keep rotating. By this action, the primary voltage is generated in accordance with the law of electric generator , which is then transformed into a very high secondary voltage exactly on the lines described in the battery ignition system. Generally magneto system is used in high speed engines like scooter, racing cars aeroplanes etc .
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