Concerning CDI's

[twitch]

I have two questions about CDI's.

First: What exactly is the CDI? I mean, is it the "brain" of the scoot, or is it simply a relay? By "brain" I mean the electronic control module like is used in cages.

Second: If it is just a relay, is there a way to bypass it and still have a working bike? I ask cause mine is bad and I have a new one ordered, but have no clue how long it will take to arrive. Since my bike is my only transport, it is kind of a big deal if I CAn bypass it.

[Jacine]

Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in motorcycles, lawn mowers, chain saws, small engines, Turbine powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive ignition systems, making the ignition system more suitable for high engine speeds (for small engines, racing engines and rotary piston engines). Capacitor discharge ignition uses capacitor discharge current output to fire the spark plugs.

Most ignition systems used in cars are inductive ignition systems, which are solely relying on the electric inductance at the coil to produce high-voltage electricity to the spark plugs as the magnetic field breaks down when the current to the primary coil winding is disconnected. In a CDI system, a charging circuit charges a high voltage capacitor, and during the ignition point the system stops charging the capacitor, allowing the capacitor to discharge its output to the ignition coil before reaching the spark plug.

A typical CDI module consists of a small transformer, a charging circuit, a triggering circuit and a main capacitor. First, the system voltage is raised up to 400-600 V by a transformer inside the CDI module. Then, the electric current flows to the charging circuit and charges the capacitor. The rectifier inside the charging circuit prevents capacitor discharge before the ignition point. When the triggering circuit receives triggering signals, the triggering circuit stops the operation of the charging circuit, allowing the capacitor to discharge its output rapidly to the low inductance ignition coil, which increase the 400-600 V capacitor discharge to up to 40 kV at the secondary winding at the spark plug. When there's no triggering signal, the charging circuit is re-connected to charge back the capacitor.

The amount of energy the CDI system can store for the generation of a spark is dependent on the voltage and capacitance of the capacitors used, but usually it's around 50 mJ.

CDI modules can be generally divided into two:-

AC-CDI - The AC-CDI module obtains its electricity source solely from the alternating current produced by the alternator. The AC-CDI system is the most basic CDI system which is widely used in small engines.

DC-CDI - The DC-CDI module is powered by the battery, and therefore an additional DC/AC inverter circuit is included in the CDI module to raise the 12 V DC to 400-600 V DC, making the CDI module slightly larger. However, the vehicle that uses DC-CDI system has more precise ignition timing and the engine can be started easier when cold.

So to answer your question, the CDI is not a relay but contains the necessary components to fire the spark plug based on the tuning of the engine. It also usually has a rev limiter built in. Depending on the type of scooter it may be possible to use another CDI and get it to run.

[AZscooter]

Jacine
Karma to you. I find you explanations on this forum consice and understantable.
Thanks for all your input.
Mike