Typical coil charge times

[Ed Lansinger]

Someone, I think it was Bill Lewis (my stupid mail program tossed the
message), wanted to know if distributorless systems took advantage
of the additional charge time, perhaps for the purpose of using
cheaper coils.  The writer also inquired about "typical" charge times.

I don't have an answer for anything in production.  I can say that when
I was working on ignition systems at school having a distributorless
system, or specifically a multiple-coil system, allowed me to take
advantage of larger dwell angles (i.e. hit higher RPM's) than I would
have with a conventional distributor.  The important difference is the
multiple coils, though, not the lack of a distributor per se (an old
Mercury outboard motor I worked on had two coils and a distributor to
allow increased dwell at high RPMs).

The system I developed at school aimed for a coil current of 10A (using
a coil pack from a Dodge Spirit R/T).  The charge rate was 1.4A/msec,
so I would charge for at least 7msec.  Current limiting circuitry took
care of any excess time.  Through experimentation I had determined that
with that coil/drive circuitry/wires/plugs combination, just under 4 msec
was the minimum time I needed to reliably fire a spark with the plugs out
of the engine.  In the engine with 12:1 compression and swirling fuel
and air I figured I was going to need more.  How much more, I don't really
know and never really got to test, but I do know that the engine would
comfortably achieve 11,000 RPM without breaking up which would have been
just about 4.0 msec of charge time.

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Ed Lansinger
General Motors Powertrain
Powertrain Control Center
Premium V Software & Calibration Group
Milford Proving Ground, Milford, MI
elansi01 at mpg.gmpt.gmeds.com  8-341-3049  (810) 684-3049
The crepes a l'orange stated above are mine, not my employer's.
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