ABSTRACT
The simplified ignition system described above would not work very well because the induced voltage in the primary winding would be strong enough to bridge the contact breaker gap and carry current to earth. This would reduce the secondary voltage and also lead to excessive sparking at the contact breaker points; the
to Motor Vehicle
points would ‘burn’ and the efficiency of the system would be seriously impaired. This problem is overcome by fitting a suitable capacitor (approximately 0.2 mF) across (in parallel with) the points. Figure 27.6 shows the capacitor in a circuit. One
terminal of the capacitor is connected to the low-tension connection on the distributor and the other terminal is earthed. Capacitors store electricity so that when, in the case
of the coil ignition system, the contact points begin to open, the self-induced current from the primary winding will flow into the capacitor instead of ‘jumping’ across the points gap. This flow of current will continue until the capacitor is fully charged. When the capacitor is fully charged it will automatically discharge itself, back into the primary winding. This capacitor discharge current is in the opposite direction to the original flow and it helps to cause a rapid collapse of the magnetic field. This, in turn, leads to a much higher HT voltage from the secondary winding.
