I believe that I have the definitive analysis of why the current through
the spark plugs is NOT supplied by the capacitor.
I humbly believe that Barney has made another mistake in his anaylsis: he
refers to a 'wad' of electrons being built up on the capacitor when the
points open, but in fact, it is the reverse, the plate (terminal) of the
capacitor that is connected to the points is depleted of electrons -- as
the points open, the current flow is into the capacitor, but as we all
know, electrons are negatively charged, so for current to flow into the
capacitor, electrons must flow out of it.
Check the graph -- you will see a large positive voltage spike on the points.
Now, the current in the secondary: as we all know, electrons flow from the
centre electrode to ground. So, they must flow in this direction through
the secondary. This would further deplete the number of electrons in the
capacitor. However, another source of electrons is current through the
primary windings and from to the battery.
All this implies a small reverse current in the primary.
Some of the peak current will also be provided by parasitic capacitances in
the wiring. This will reduce the visibility of this current when measured
in the primary windings.
Let the flames begin!
Simon
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Simon Matthews MailTo:simon_matthews@avanticorp.com
'57 MGA
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