What Does a CDI Box Do?

Commodore Gandalf Cunningham/CC-BY-SA 2.0

A CDI box is a Capacitive Discharge Ignition found on most bikes and is linked to the ignition, where it stores an electrical charge and increases the power of the spark in the spark plug. A CDI box can only be found on vehicles that are gasoline engine based.

The ignition system has several parts, and these parts are all important when learning about the way the CDI box works with the ignition system. The parts include the flywheel, the stator, the charging coil, the hall sensor and the timing mark. The flywheel is a permanent magnet in the system that spins on a crankshaft. The stator is a plate that can hold the electrical wire coils that work to power the lights, battery charging circuits and ignition. The charging coil is a coil that is found on the stator and produces power for the flywheel, condensor and spark plug. The hall sensor will measure the point where the flywheel’s magnet changes from the north pole to the south pole and will send a pulse to the CDI box. This pulse will trigger the CDI box to move the energy that it has obtained from the capacitor to the high voltage transformer. Then the timing mark is simply an alignment point that the stator plate and engine case share. This “mark” is useful because the stator plate can be rotated left and right according to the mark and it will change the trigger point of the CDI.