Beginner coil thoughts

To: tesla-at-pupman-dot-com
Subject: Beginner coil thoughts
From: "FRITZ, TERRY" <terryf-at-ftc2.aei-dot-com> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Mon, 16 Nov 1998 20:42:46 -0700
Approved: terryf-at-verinet-dot-com

Hi All,

	It occurred to me why my GM HEI ignition coil system can push 10 inch
sparks when experiments of pulsing the primary of a stock coil with 250
volts and such only produces sparks of a few inches.  The key was my
removing the core.

	Originally, the primary will have 12 volts energizing the core.  However,
at 200 or 600 volts the core simply saturates and acts like a short (and
the over-current blows the primary).  Core saturation is what is limiting
the stock coils.  When the core is removed, the saturation problem is
eliminated.  
	
	Removing the core also removes the high coupling from primary to
secondary.  So you still will not get much out of it.  However, if you now
tune the primary and secondary to resonance and turn it into a Tesla coil
circuit, the voltage is then allowed to fly up to the 200X primary voltage.
 That is what I did and that is why I got very big sparks.  The operating
frequency is also vasty improved too but the secondary will still limit the
frequency to the 10kHz range.

	This does make the GM HEI coil unique in that the cores are so easily
removed.  The Mallary, Accell, Jacobs and other fancy rod shop coils don't
have removable cores as far as I know.  This will eliminate them for my
uses.  Thanks to everyone that suggested them anyway!

	 One bit of good luck.  I went to the parts store and bought a brand new
generic HEI coil for $14.  I instantly noticed that it was EXACTLY like my
original GM coil.  No GM part numbers or anything like that but it was
definitely made by the same OEM.  The advantage here is that I paid $15 for
something that would cost $70 from the GM dealer.  The inductances and all
that should be just the same.  So a new coil, which my testing showed is
better, is definitely the way to go and it is very economical to buy too!

	 It looks like this will work out pretty well at this point.  Having to
use the mineral oil is sort of a pain.  It will give the beginner a chance
to use mineral oil which will demonstrate it's uses and the potential mess.
 Lots of dish washing detergent is the key to keeping it under control!

     So the cost so far is as follows:

Primary cap		$10
HEI coil		$15
Mineral oil		$3
600 volt source	??
other stuff 	free?

Total		$28

	Not bad at all!  The charging circuit will be challenging in keep safe and
cheap.  Electrically there are many options.  Just have to select the best.
 Probably won't be running at 120BPS but even at 1 BPS it is really neat
and will provide the needed "thrill" value.  Perhaps I can push the power
up even more to get longer sparks!  You know how this Tesla coil stuff is
:-))  

	This would allow a common platform for a little competition.  I don't
think hooking a 20kW pole pig to these HEI coils will allow that old trick
to work anymore :-)

	At this point, I will go ahead and claim to be the present holder of the
GM HEI Coil Spark Length Record  (GMHEICSLR)  at 10 inches :-)    Remember,
I haven't even tuned it up yet!  As far as I know, my distant competitors are:

Ed Phillips		3.5 inches
Sam Barros		1.5 inches
Terry Fritz 	10 inches

Of course, that was my first attempt.  The epoxy is drying on number two
(20 inch possible) right now ;-)



	Terry
	Holder of the coveted GMHEICSLR :-))