Date:         Wed, 1 Oct 2003 16:12:19 -0700
Reply-To:     Pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Pensioner <al_knoll@PACBELL.NET>
Subject:      Re: The details of Motronic (long but no cigar)
In-Reply-To:  <200310011952.h91JqsCH166810@mailapps4-int.prodigy.net>
Content-Type: text/plain; charset="iso-8859-1"

The time the points are closed is the dwell time allowing the current
through the primary to create magnetic field saturation in the windings of
the coil.  The capacitor just keeps the points from "burning" when the gap
is opened and the current suddenly drops to zero.  This change in the
current from saturated value to zero causes the collapse of the magnetic
field in the coil and the change in the magnetic field from saturated to
zero in a very short period causes a high voltage to appear across the
secondary.  This is what causes the spark to occur. The voltage induced is
proportional to the first derivative of the current with respect to time.

That is in a Kettering or points coil type of ignition.  A magneto operates
differently.

The Subaru ignition operates by sequencing driving pulses to an ignitor
amplifier which feeds high current pulses to coil over plug ignition.  One
coil per plug.  Governed by the cam position and crank position sensors and
various other parameters.  Individual control on a per cylinder basis.

"It's just fizzix, it's always just fizzix"  -- Feynmann

DwEEb