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Re: ignition coils

Hi Kevin,

	I just posted this to the list the other day but you and some others may
have missed it.  It seems like a popular post.

Cheers,

	Terry


==============================

Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi Nick,

	First of all let me say be VERY careful with these coils.  The ~10kHz
operating frequency is WELL within what you nerves will feel.  A shock form
such a coil will send you through the ceiling!!!  Yes I have tested it! =8-O

When you hooked the coil up to the dimmer, it probably quickly overheated
which contributed to the early breakdown.

So here's how to make it:  

1.	Get a brand new GM ignition coil (76 Cadillac 500 cid engine) from the
cheap auto parts store (~$15).  Old ones out of cars will have cracks and
flaws in the vacuum impregnated core which will fail in this ~200kV service.

2.	Grind off the welds on the outer steel laminated care and discard it.
Beware the very sharp edges.

3.	Epoxy a 16 inch long 2 inch diameter PVC pipe over the high voltage
button.  Solder long wires to the primary connections and connect the
secondary ground lead to a wire connected to a good earth ground.  Position
the coil in an oil bath with the tube pointing up.

4.	Fill the tube with oil too so that the whole thing is in, and insulated
by, oil.  You will have to space the coil off the bottom of the container
too so there is about an inch of oil there.  There is a lot of HV in a
small place so the oil is all that is keeping the thing together.  I put it
all in a big pan to collect the coil if something goes wrong.

6.	Position a metal rod down the center of the tube and place some little
ball or something on the top for a terminal.

7.	The spark gap will have to fire at about 1000 - 1500 volts.  I used two
sharpened nails that points could be closely adjusted to about 1 mm (that
is a millimeter ;-)).  Tungsten would have been the material of choice.

8.	I used 0.1 uF 630V poly caps (well over their rating, EMMC work was
going on then too...) for the primary cap.  I needed 1.7uF in the primary
but your mileage may vary.  I added or subtracted caps to adjust the value
for the best spark.  

9.  I used a high voltage (rectified ignition coil) power source to slowly
charge the primary cap up.  The wider the gap the longer the sparks.  Don't
go over one pulse per second or the coil will die too soon.  10 inch arcs
at 1000 volts seemed pretty safe.  1500 volts at near a foot is getting
close to the destruct point of the coil.

I got 13.25 inches from one (single coil not two - that's cheating ;-))
coil to a pointed ground rod before I blew my best setup.  This all shows
dramatically the advantages Tesla coils have over conventional transformers
for making big sparks.  You would be very lucky to get a 6 inch spark out
of a GM coil using it as a transformer or induction coil.  The steel core
will saturate and et up all the power after a certain point.  With the core
removed, you have a True Tesla coil air core resonant circuit that can
develop as much voltage as the epoxy in the coil will stand.  I cut open
and examined a number of coils I blew.  One was defective, one was cracked,
but the 13.25 inch one was perfect.  Ford also makes a similar ignition
coil but I have never tried them...

I wanted to make a simple "beginners" coil with this project but the whole
thing quickly got too dangerous.  Be very careful with these simple but
potentially deadly coils!

Some Zipped JPG pictures are at:
http://users.better-dot-org/tfritz/COIL.ZIP

A search of the archives at www.pupman-dot-com for "GMHEICSLR" will pull a
number of old posts on this like:
http://www.pupman-dot-com/listarchives/1998/November/msg00694.html

	Terry
	Still proud holder the coveted GMHEICSLR* at 13.25 inches. :-))

*General Motors High Energy Ignition Coil Spark Length Record

Don't EVEN think of trying to take the coveted GMHEICSLR* away from me
either ;-)))

===================================



At 10:38 PM 01/07/2000 -0500, you wrote:
>Can someone offer some good instruction on how ignition coils can be used
>for tesla coils.  I have a small system just getting sparks between two
>coils.  I have read about ignition coils and tesla coils but am not getting
>the full picture, can you make one from the other?
>
>thanks
>kevin wahila
>