Ah, 15A peak. That were the old days.
Certainly, the dI/dt in the moment of switching off the coil is important. But IIRC I calculated something in the 10µs range to get the 500V on the primary side. But I may be wrong. Anyhow, 10µs isn't that fast and I even don't switch off as fast as I can.
Right. That's what's happening if the secondary has no spark plug connected. Some of the cheaper ignition systems warn you of that problem. The coil's isolation won't be good enough. With my vacuum-impregnated coil and the voltage-limiting on the primary, that doesn't happen.
Slow and "big" coils (high R_i and high L). As I said, my coil has a charge time of 0.5ms, even "fast" coils (the big type know since decades) do have several ms and their limit is at about 200 sparks per second with already reduced energy. I couldn't measure it right at the moment I tried because I lacked a suitable power-supply (now have one). But it looks like I get about 1000 sparks/second out of that coil. I really don't know wether there is some such thing like recovery time (for the coil), but I'll investigate on that later.
Thanks for the explanation. Looks to be too complicated to do, except for one-offs. I can't measure the capacitance of the coil, but it *looks* like I didn't make a bad job (looking at the rise-times on the secondary). I learned, that the inter-layer isolation reduces capacitance too. The means is simple: Increase the physical distance between windings with a high voltage difference.
Thanks for your input, Nick