DeTomaso Mailing List: March 2000, Message #58

Well, I will admit, I didn't read the whole thing, but I think Andy was
referring to the dual-post coils that are used on many distributorless
ignition systems these days.

As I understand them, the coil on a standard car fires once for each
cylinder, this is done by the coil acting like a large capacitor (not
exactly mind you) whereby an electrical field is generated then released,
on cue.

In the dual post coil, what is being taken advantage of is the subsequent
"collapsing" field after firing.  This field is strong enough to fire the
oppossing post.  Thus, a dual post coil has the affect of firing both in a
"forward" and  a "backward" field direction.  This does NOT however mean
that it fires the opposing post at a polarity reverse that of the primary.
It simply uses the collapsing field to generate another "shot" of current
to another plug.

It's kind of like if you ran your alternator backwards, you'd still
generate a charge (except that you'd probably fry the diodes, I can't
remember) in the same direction as before.  It's all dependent upon
electronic field affect.  A coil is nothing more than a transformer that
multiplies the voltage to the plug.  A transformer works on a field effect
theory, whereby the primary and secondary windings are not connected to
each other, but are rather in proximity to each other, such that the
ensuing magnetic field induces current flow to the other.  Somehow this is
taken advantage of  in a dual post distributor.  I'm not really up on the
exact science.

And now that I've totally confused myself, does anyone want to straighten
us out?

Asa Jay

At 12:56 PM 03/02/2000 -0500, Steve Liebenow wrote:
>As a hardware engineer.... I have a real problem with a software type
>trying to esplain hardware functions.....  :)))
>
>Andy's description of the wasted spark theory has my brain buzzing
>backwards.... not getting into the theory of electron flow and
>what-have-you.... but, how can a plug fire backwards when the ground
>potential is the same as another plug....
>
>The plug fires, just during the exhaust stroke... just like Harleys....
>just like the wife-taxi (92 Ford 4.6V8) which use coil packs...firing two
>plugs each....
>
>Nice esplanation... I don't buy it....  current flow does not reverse thru
>the engine block..... in a dead cycle.... just no compression to do
>anything!  Sorta like trying to lite a burp instead of a fart..... ?  HAH!
>
>Are we both seeing something wrong here???
>
>$.03
>Steve
> 
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Asa Jay Laughton
Global Handheld and Mobile Systems (GHAMS)  Engineering

Itron, Inc.
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