Re: Ignitions

[Steve Stegmann <stegmann@domain.elided>]

I can't imagine why you would want to vary the amount of voltage to the
coil. The goal is to get the magnetic field of the coil as saturated as
possible.  Then the spark is generated when the field collapses.  This is
how the typical points work, and the older electronic ignitions which are
just replacing the points with solid state. 

In the MSD (& probably the Jacobs) and all modern OEM systems I believe
the spark is generated on the rise of the magnetic field in the coil. 
This rise is provided by discharging a capacitor through the coil.  It
builds the field faster because the spike from the capacitor rises to its
peak (200 volts maybe) much quicker than the 12 volts from the points
collapses to zero.  The faster you can build or collapse the field, the
quicker you can build the secondary voltage, the less chance it has to
bleed off before the plug fires, the more goes through the plugs.  And, at
50,000 to 80,000 volts it leaks like water through a diaper. 

The other deal is the capacitor charges faster than the coil so you can 
fire the plugs more often, and at higher voltage.  You no longer have to 
wait for the 12 volts to charge the coil, it's just used as a transformer.

The spark can be generated by the buildup of the field or the collapse of
the field.  All that is really needed is for the field to be moving.



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Steven A. Stegmann
     _/_/_/    _/      _/_/_/ "No free man shall ever be debarred the use
   _/    _/   _/_/   _/    _/  of arms.  The strongest reason for the 
   _/        _/ _/   _/        people to retain the right to keep and bear
    _/_/    _/  _/    _/_/     arms is, as a last resort, to protect 
       _/  _/_/_//       _/    themselves against tyranny in government"
 _/    _/ _/    _/ _/    _/    
 _/_/_/  _/     _/ _/_/_/         Thomas Jefferson, June 1776
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