triggered gap idea

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

There has been much discussion on various and sundry triggering circuits
for a triggered gap.  Since most of us are using auto ignition coils,
rather than cobbling up something from dimmers, etc., why not just use the
electronic ignition amplifier that typically accompanies that HEI coil.

In several systems I've built, I've used various MSD ignitions to fire an
auto coil from a TTL timing source.

Wretchedly expensive if bought new, but, if you're scrounging coils at the
junk yard, you might be able to grab the solid state driver as well, since
it's all encapsulated in the distributor.  Maybe a good source would be the
ones that Ford is replacing in the big recall?  They don't meet car spec
(temperature related failures, I believe), but they'd be more than good
enough for triggered gap use.

These amplifiers typically trigger of a very small pulse from a magnetic
pickup, and should be readily adaptable to being triggered of an
optoisolator or 555 or something sync'd to the power line.  Modern
ignitions need to time the spark to better than 1 degree of crank rotation
at 6000 RPM (= 100 RPS = 10 mSec/360 = 27 microseconds) to meet emissions
requirements.  All you'd need is a beefy(probably 5A minimum...)12V supply
to run them.