Re: double firing power pack?
Hello Jeff,
I try to tell you my ideas, sorry for the english.
On the flywheel plate there is a sensor coil with a north and a south pole, generating a positive and a negative voltage with each revolution.
Only the positive voltage is needed for triggering a thyristor SCR) in the powerpack (CDi), by which the voltage of a charged capacitor is switched through to the high voltage coils to initiate the ignition at the right time.
The negative sensor voltage pulse is normally short- circuited through a diode so a second trigger is suppressed.
Remember a two stroke engine normally only needs one spark / cylinder / 360 ?.
If the diode in case of a fault has a high instead of low resistance the negative voltage pulse will trigger the thyristor a second time wihin one revolution and you may have double firing.
Normally if the flywheel key is in a correct position this shouldn't be a big problem, because combustion only takes place with sufficient compression of the gas/air mixture.
If the piston is in down position there is no compression at all and so a second spark will cause no further firing.
Problems may only occur when firing takes place in a piston position with sufficient compression in both directions.
I hope I explained it clearly enough.
Greetings from Germany
Peter
