- CDI systems are used in many motorcycle engines.motorcycle image by Greg Pickens from <a href='http://www.fotolia.com'>Fotolia.com</a>
Capacitive discharge ignition, or CDI, systems have been in use since the 1960s. These electronic ignition systems are one of two varieties of ignition systems in use, with the other being induction ignition, or transistor controlled ignition. CDI ignition systems trigger transistor switches using sensors and are mainly used for marine, aircraft and automotive engines. - Capacitive discharge ignition systems store energy in an external capacitor. When required, that energy is then discharged into the primary ignition coil winding. This generates a voltage high enough to ionize the gas between the spark plug electrodes of the secondary coil winding. This creates a high-current spark.
- Capacitive discharge ignition system coils are not powered; the module sends a pulse through the coil that is roughly 250 volts, and the coil multiplies this voltage. The CDI coils commonly used today amplify this voltage 100-to-1, and an average 250-volt output becomes a 25,000-volt output. The spark lasts for approximately 10 to 12 microseconds. Some CDI coil outputs can reach up to 40,000 volts. In comparison, transistor-controlled ignition systems have coils that are powered at 12 volts and collapse to spark on command from the ignition module.
- An advantage of capacitive discharge ignition systems is that since CDI engines have no moving parts they require little maintenance. Also, the intense, fast-rising spark generated by these systems reduces fouling, which is especially beneficial for low-efficiency engines. Disadvantages of CDI engines are that the spark plugs have limited lifespans, and these systems use expensive electronics, making them pricey to replace.The reliability of CDI engines has been questioned extensively, as some components are sensitive to vibrations, power surges, moisture, thermal stress and heat.
How CDI Works
Power
Advantages and Disadvantages
SHARE
