Saturday, March 28, 2009

How works CDI

Since I need to modulate the engine power, I need to understand the CDI technology:

Capacitor
The Capacitor is the main component: in the fist phase it is charged whle in the second phase it is discharged trought the coil and the spark. Typically is value is from 0.47uF to 2µF .

Switch
The Switch element has the purpose to transfer the energy from the capacitor to the coil, typically it is composed of one SCR ( Silicon Controlled Rectifier) or TRIAC combined with one diode for the reverse current coming from the ignition coil.

Ignition coil
The ignition coil has the goal to increase the voltage to 5 .. 20 kV

Spark plug
The Spark is such component capable to fire the combustible mixtures. The mixutures could start burning only if about 20 milli joules will be given to it.

Finally also a position sensor and an CPU is required:


Let's try to understand the hot part:


Seems that when the SCR start to be conductive, the current Ith goes from the capacitor to the coil, while the negative impulse is conducted by the diode. Finally the current that goes into the coil is:


Uhmmm.... this is not all what I would need to fully understand it, but is a good starting point!

Sito segnalato da:

La risorsa Italiana per l'elettronica.

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