i know im not the questionee here, but when i was making these things, i could get a spark from the 15 volt winding of a regular AC transformer. ie, 15volts, RMS. at 50Hz. it also burnt out resistors, im guessing because of too much current flow. fine on the engine, even 1/4 watt ones, but 5w ones would start smoking and turn brown on standard 50Hz AC!
the stock cdi couldnt do a thing until i got to 30+ volts.
no difference in output sparks either, once sparking.
remember that the output of the HT also is NOT a sine wave.
the multimeter test is just that, a test. not a definitive result. it shows the things work!
whats needed for true readings of output voltage, which also varies depending on load, is a silly scope.
(oscilloscope if you arent familiar with the most necessary tool of electronics)
this way, you not only get an idea of the shape of the waveform, you can get an average voltage output. remember, its a slope. the peak voltage is not the same as the "average" voltage, which is what RMS means. root mean square, or about 0.707 of the actual peak voltages.
just about every CDI unit, be it the self powered ones on HT's or pitbikes or dirtbikes, use roughly 400V RMS. RMS doesnt work if the waveform isnt a sine wave. so you may get a peak voltage of 600-700 volts. while a RMS meter will only read 100 volts or so.
battery powered CDI units have an inverter circuit, converting DC 12v (or whatever the power supply is) into, you guessed it! approximately 400 volts.
further complicating the issue are the diodes, which always drop 0.7 volts, and any resistance in the circuit, and the "chargeability"(ooooh, no spell check so it must be a real word!) of the capacitors. a capacitor NEVER fully charges, nor will it completely DISCHARGE, even when short circuited.
well, not very quickly, at least... especially if theres any resistance. the basics of the CR timing circuit. and every conductor has resistance. excepting superconductors. which are another kettle of fish. ohms law breaks down completely as soon as theres a 0 in the equation... 1000000 volts = infinite current x zero resistance. substitue one millionvolts for any voltage....you still get infinite current. think about it
you cannot multiply or divide by zero! super conductors dont actually conduct electricity. more like standing waves of energy. induced currents, that never fade away, unlike the LC tank circuits used in a radio, for instance.
fiendishly complex, electricity. its like juggling eels! one part affects another part and you gotta keep your eyes on everything at the same time... oh, the basics are simple enough, but it can get rather confusing if youre not careful.