Re: Ref: RRich,LEVE,others... : Dspark Ign Mod Qua
DC is used as pulsed DC. On Off On Off.
The coil is a transformer of sorts, but it's an auto transformer (not to be confused with automotive transformer.)
Kinda the same idea as a flyback transformer - kinda.
The primary and secondary are wound backwards as opposed to a regular transformer, and the secondary (bottom end) is tied to the primary (top end.)
And it uses an iron core.
When current flows - module's on or points are closed - a magnetic field builds up - lots of energy goes into the iron core - you can say that energy is "stored" there for awhile. Charging time is called dwell. If it was a regular transformer it would have a big output - 12 volts multiplies by the turns ratio, but this doesn't. You can barely feel it.
Once charged with lots of energy and it's "ready," the module stops current flow.
The magnetic field collapses - a voltage is induced in the secondary like a regular transformer - maybe 500-1000 volts, depending on the turns ratio.
BUT----since it's also collapsing around the primary it too develops a big voltage - about 250-300 volts. Since the primary is feeding the secondary through the internal connection, that voltage gets multiplied by many times - essentially the turns ratio - and that voltage adds to the other secondary voltage.
Makes big spark!
Sounds goofy, but it works. That's called the Kettering principle.
So -- the big secondary spark happens when the primary current goes away!
The HEI just does it better than most everything else.