Paul -

I've been lurking on your CDI info flow lately, and chatted with
another EE friend about it.  He was interested enough to look up specs
on the chips you're using, and find alternative designs.  He sent me
this to read:
    http://www.molla.org/DIY-CDI/SC-DIY-CDI-article-hires.pdf

I certainly don't want to devalue your effort thus far - in fact just
the opposite.  I am personally getting some interesting design
explanations by reading the article, and hope that you might gain some
useful info as well.  In essence, the article may prevent you (us)
from reinventing the wheel - something you often preach re: cooling
designs.

If you want to group to read the article, and if it doesn't simply
regurgitate stuff you already posted, feel free to post the link.

-Vince Orton

That is the Aussie system I have been talking about.
You must have missed it. Here is one of the early
messages on the subject.

Paul Lamar

Paul -

At first glance the circuit discussed in:
    http://www.molla.org/DIY-CDI/SC-DIY-CDI-article-hires.pdf
may appear to be the Aussie system you've been talking about, but it
isn't.  Similar, but different.  I'll refer to it as the "John Clarke
System" - the author of the Silicon Chip article.  I'm learning A LOT
by studying it.

The nice thing about the article is that it explains IN DETAIL each
stage of the circuit, and options for changes.  I recommend taking the
time to read it for anyone seriously interested in CDI for aircraft
and rotaries - if only for educational and research reasons.  Mainly
to keep from ... reinventing the wheel.  It's a 1997 article, so some
improved chips should be used in new circuits.

Some nice features of the John Clarke System:
- Open source (and yes, there are other contributors of changes &
updates - google it)
- Multiple spark output - multiples of two strikes (2, 4, 6, etc.)
- Operates on reluctor, points or Hall effect signals.
- Usable to beyond 1000 sparks/second (60,000 RPM for 1 coil/sparkplug).
- Regulated 300V supply for consistent spark energy.
- High frequency operation eliminates audible oscillator noise.
- Efficient circuitry for minimum heat generation.
- Needs only 9V to start, but then keeps operating down to 5V -
important in aircraft!


Now on to a few thoughts on the Aussie system ...

In general, I don't think shared high voltage pulsing outputs is a
good idea.  Especially when some are pulsing high voltage, and others
are "yanking" to ground.  They are bound to eat each other's energy.

The Aussie circuit diagram (as you've published in ACRE) has the 4
stages all pulsing the same coil line at 600V.  I strongly suspect
that when one stage fires that there is some serious back-EMF into the
other 3 stages.  You mentioned that the output FETs in the Aussie
system were blowing.  Probably related.

600V into a coil may lead to internal breakdown.  It seems that a 300V
target comes up a lot, with a few warnings about excessive voltage
burning out coils.

I hope you enjoy the John Clarke System article, and find it worth the
time to read.

-Vince Orton

John Clarke is an Australian. Silicon chip is an Aussie magazine
as I recall.  If there are any differences it is due to the way
it is written up. John Clarke apparently did not author either
article. Some of the illustrations are identical. The second
one has a better parts list.

The design has one or two flaws namely it's sensitivity to input
voltages less than about 9 volts which causes one or more FET's
to blow. In the unit I was given that had happened more than
once. It is based on the IR2155 which has been improved to deal
with that situation. The ST L6384 has been improved over the
old IR2155.

We will find out if it works or not.

Paul Lamar