A capacitor discharge ignition or CDI works by passing an electrical current over a circuit capacitor. This type of ignition builds up charge quickly. It is ideal for smaller vehicles and motors.
A CDI ignition starts by generating a charge and storing it up before sending it out to the next component in the system. Once the electrical level reaches a proper value, the current signals and charges a spark plug that lets off its excess electricity in pulses that power the engine. This power passes through a capacitor and is transferred to an ignition coil that helps boost the power by acting as a transformer and letting the energy pass through it instead of catching any of it. CDI ignition systems therefore allow the engine to keep running as long as there is a charge in the power source.
CDI ignition systems have fast charging times and power themselves more efficiently than inductive ignition systems. These types of power sources are ideal for smaller machines such as motorcycles, chainsaws and outboard motors.
Despite its usability, there is a limit to the amount of charge a capacitor holds before it burns out, so it is not a usable resource in larger machines and vehicles. The faster a CDI system spins, the less power it exudes, and therefore it cannot successfully power a car or truck.