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From: awalker@topaz.ARPA (*Hobbit*)
Newsgroups: net.auto
Subject: Zap!
Message-ID: <217@topaz.ARPA>
Date: Fri, 11-Jan-85 02:23:13 EST
Article-I.D.: topaz.217
Posted: Fri Jan 11 02:23:13 1985
Date-Received: Sun, 13-Jan-85 07:50:39 EST
Distribution: net
Organization: LCS Expert gang, Rutgers
Lines: 37

Want your points to last forever?

It is real easy to upgrade a ''standard'' points-capacitor-coil ignition
to an electronic version that will deliver close to twice the spark power
of the stock ignition.  I put one in my 4-by project and it's been kicking
out the EMF ever since.

Basically you place a two-transistor amplifier between the points and the
coil.  However this involves moving the capacitor so that it is in parallel
with the coil rather than the points.  This allows you to use the points as
a low-signal switch, and the coil/capacitor circuit to resonate when the 
points open.  It's this resonance that actually generates the spark.  Since
the fall time of a transistor is so much faster than a pair of points, you
get a bigger bang from the business end of the coil.  At this point, the 
question about eliminating distributors becomes academic.

The problem with stock ignitions arises just when the points open.  At the
exact time when they start to separate, coil current falls.  The coil, as
most coils will, tries to compensate for this current drop by generating
a 300 or so volt backlash, which the secondary picks up and turns into your
15 or so KV.  But as the points open wider, the voltage across them increases
at the same time, so you get a spark.  This makes a raggedy falling-edge
situation at the coil, and tends to reduce the output voltage.  Since the
transistor unquestionably turns *off* when the points open at all in the 
amplifier circuit, you get a nice clean falling edge and the coil generates
its backlash against the resulting *zero* voltage instead of whatever's 
left around from the sparking.  So you get a much heftier kick at the
secondary.

You have to find a transistor whose VCE is close to 400 volts, or the
backlash will kill it.  You could even replace your points with an inductive
or IR pickup, but I didn't bother with that, because just in case the 
amp *does* die at 3 in the morning and I don't have an extra transistor
with me, I can switch back to regular ignition mode and get home.  I haven't
had to do this yet...

_H*  [here, just hold this wire for a sec]