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From: firstname.lastname@example.org (Bob Wilson)
Subject: Re: CDI Ignition Circuit
Date: Sat, 02 Nov 2002 04:51:34 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article <4JmdnVk967vsBF-gXTWc2Q@comcast.com>, email@example.com says...
>Am looking for a simple CDI circuit to use on a Kettering equiped Kohler
>engine. I want to maintain the points and condensor.
>I have already produced the Inverter, but need circuit to trigger SCR
Delete the "condensor" it is useless and causes points wear excessively when
triggering an electronic ignition. Triggering the SCR via the points is
trivial. The points open when it is time to fire the plug, so all you need
is to feed the points via a load resistor from 12V, then just buffer this
signal to the gate of the SCR using capacitive coupling. This will trigger
the SCR with a narrow positive-going edge, but won't try to keep the SCR
gate biased ON after the energy storage cap has discharged into your coil.
This allows your inverter to start recharging the energy storage cap almost
immediately after the spark is over, instead of forcing the SCR to stay ON
until the points close again. Use a points load resistor that will allow
wnough points current to clean the points, yet not wear them out prematurely
(a points current of half an amp is a good compromise).
There are all sorts of schematics for these things out there, since people
have been building them for years (I built one in the '60s!).
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