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CDI System |
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The essential feature of Capacitator Discharge Ignition (CDI) systems and what differentiates them over conventional electronic systems, is that the ignition energy is stored in the electrical field of a capacitor at approximately 400 volts. The storage capacitor is charged either with a constant current or with pulses. Regardless of the method, the charging stage contains a small transformer which boosts the voltage level to approximately 400 volts in order to achieve the required stored energy results. At the ignition point the thyristor is triggered. The capacitor then discharges via the thyristor to the ignition coil. The main advantage of CDI systems is their virtual insensitivity to electrical shunts (eg fouled plugs) in the ignition circuit. Originally designed in the late fifties, they were intended for higher revving applications, where their high intensity / short duration spark increased the total spark energy available over points systems, and was able to ignite mixtures more effectively. Another feature of some of these CDI systems is their multiple sparks at low RPM (usually under 3000 RPM, and particularly below 1000rpm), increasing the total spark energy available. However, these multiple sparks always diminish with increasing RPM until a single spark is left above 3000 RPM. The most common CDI system that most people in the performance arena have heard of is the MSD range of high performance ignition systems. CDI systems can be triggered either by breaker points, (ie: an original single point distributor - as the role of the points is not critical with the CDI system) or inductive type pulse generator, (as found in many O.E and aftermarket electronic distributors). CDI systems also employ coils specific to their method of operation and should not be used with coils from other systems and vice-versa. They must also never be used with straight wire plug leads as this will cause massive interference with the units themselves and other electrical equipment as well as arcing to earth through the leads. |