bigger capacitor requires more current at a given voltage to charge the same amount in the same time. quite simple really.
the magneto cant generate enough voltage which is dependent on the current required.
the size of the cap has no bearing on spark duration. discharge it into the same resistance, ie, the coil primary, it just delivers more current. unfortunately the step up works on voltage rather than current.
ohms law sneaks back into electronics at every turn, no matter how hard one tries to defeat it!
farad... 1 amp at 1 volt for 1 second... or a coulomb or something...
love wiki at times, it always backs me up
Definition[edit]
One farad is defined as the capacitance of a capacitor across which, when charged with one coulomb of electricity, there is a potential difference of one volt.[1] Conversely, it is the capacitance which, when charged to a potential difference of one volt, carries a charge of one coulomb.[2] A coulomb is equal to the amount of charge (electrons) produced by a current of one ampere (A) flowing for one second. For example, the voltage across the two terminals of a 2 F capacitor will increase linearly by 1 V when a current of 2 A flows through it for 1 second.
also, the point of triggering the scr is the opposite polarity to the charging current. so the capacitance cant affect it, it being separated by a blocking diode.. though i havent verified this with a silly scope, so i could just be talking shyte.
reduce the resistance on the triggering side, voltage will increase less rapidly, due to increased current flow, trigger point will be retarded. increase resistance, and the opposite will occur.
or use a CR delay circuit.
increase current flow, and watch the gate on the SCR fry
fiddle with alternate SCR that trigger at different voltage/current levels.
or use an IGBT, that requires NO current flow to be triggered.