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Deze reply is gepost in de afdeling Main Forum in het onderwerp 'neon en die andere electriker-job 4 joe' (ID 887).
De reply is geschreven door Joost (UserID 6) op 26-6-2001?06:57.

Capacitor Discharge Ignition Circuit (CDI)

The CDI ignition circuit produces a spark from an ignition coil by discharging a capacitor across the primary of the coil. A 2uF capacitor is charged to about 340 volts and the discharge is controlled by an SCR. A Schmitt trigger oscillator (74C14) and MOSFET (IRF510) are used to drive the low voltage side of a small (120/12 volt) power transformer and a voltage doubler arrangement is used on the high voltage side to increase the capacitor voltage to about 340 volts. A similar Schmitt trigger oscillator is used to trigger the SCR about 4 times per second. The power supply is gated off during the discharge time so that the SCR will stop conducting and return to it's blocking state. The diode connected from the 3904 to pin 9 of the 74C14 causes the power supply oscillator to stop during discharge time. The circuit draws only about 200 milliamps from a 12 volt source and delivers almost twice the normal energy of a conventional ignition circuit. High voltage from the coil is about 10KV using a 3/8 inch spark gap at normal air temperature and pressure. Spark rate can be increased to possibly 10 Hertz without losing much spark intensity, but is limited by the low frequency power transformer and duty cycle of the oscillator. For faster spark rates, a higher frequency and lower impedance supply would be required. Note that the ignition coil is not grounded and presents a shock hazard on all of it's terminals. Use CAUTION when operating the circuit. An alternate method of connecting the coil is to ground the (-) terminal and relocate the capacitor between the cathode of the rectifier diode and the positive coil terminal. The SCR is then placed between ground and the +340 volt side of the capacitor. This reduces the shock hazard and is the usual configuration in automotive applications.

Hmm, meschien is het nu wat duidelijker. De honda cdi vroegt de ontsteking bij zo'n 8000 toeren omdat de zuiger dan sneller is dan het vlammen front. Zouw je niet vevroegen dan krijg je zeg maar relatief na-ontsteking.
Je merkt dat ook wel bij het rijden want meestal begint ie pas bij 8000 toeren te trekken. Voor elke toerental heb je eigenlijk een ander onstekings tijdstip nodig. Met een voledig instelbare cdi, kun je de timing zelf instellen zodat het bij jouw optimaal loopt.