Interesting articles... but I have to say that the guy at Century Performance scares me when he says a coil "has to build resistance" so it can fire. Uh, no... I'm guessing this guy doens't have much electrical background, but then, how is he making product? Anyway, Inductors, which is what your coil is, has two properties: Resistance and Inductance. Resistance is what we all know and love, measured in ohms, which is the what describes the hinderance of electrical flow. Inductance, measured in henrys (no I'm not making this up) describes a not so easy to explain property of how much energy a coil can store in its magnetic field. I guess to make it simple, it's the same thing as a capacitor, only in reverse. Confused? Good...
Coils or inductors, are interesting animals. They get bent out of shape when you either introduce a current flow to them, or, remove it once you have established one. Anybody who has been shocked when they have connected jumper cables to a *really* dead battery has experienced a very crude, but effective inductor in action.
So, for a coil to fire a plug, you don't build resistance, you build the magnetic field that is created by applying more current to the coil. (for all intents and purposes, adding more voltage adds more current since the resistance of the coil is a constant; ohm's law) Once you have enough field, you dump the current out of it, and wham, the field tries to raise the voltage to maintain the current flow, which it can't, so the voltage climbs higher. At some point this voltage is high enough to bridge what ever gaps are in your electrical system, and makes a spark. The spark is maintained as long as there is sufficient magnetic flux in the field. As this decays, the voltage comes back down, to a point where eventually the spark is extinguished. Now it's ready for the next cycle of firing.
CDI and digital systems pretty much do the same thing, but their method is a little different, making lots of pulses at a controled rate to get the desired effect. The easiest and probably the most widespread and obvious demonstration of this would be any of the newer mig welders or plasma cutters. You hear that whine they do when the arc is on? That's about 10,000 pulses a second, building and collapsing the field of the inductor inside. Truely an industrial spark box!
This concludes our class for today.
