Capacitive discharge

(CD) A type of ignition system. It can be either all-electronic or breaker point controlled. The primary power is drawn from the engine's battery and put into the CD power supply, where it is changed from 12 volts direct current to about 300 volts of pulsating direct current that is stored in a capacitor (condenser). The release of this energy through the coil is governed by a silicon-controlled rectifier (SCR). When the SCR switch is closed, the voltage stored in the capacitor is supplied to the coil, which acts as a voltage step-up transformer boosting firing voltage to around 30,000 volts to fire the plugs.