OLTC Update - The baby has arrived :-)))

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Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

Our local Tesla meet was tonight and I barely got everything together and
thrown into the car to Denver.  Lots of last minute stuff...  I got some
thick poly sheet on the way since primary to secondary arcs were a problem
yesterday.  On the way down, I decided to run it till it explodes :o))

So we got there and set it up in Bill's lab:

	http://hot-streamer-dot-com/temp/OLTC08-25-01.jpg

Note the poly sheet and raising the secondary modifications.  This was
after the primary to secondary arcing punched a hole clean through a sheet
of 3/16" G-10 (brand new too!).  The dielectric properties of G-10 allowed
enough leakage current to carbonize a path "through" the G-10.  The many
layers of poly act like many caps in series so there is very little leakage
current.  A great trick!!  After these mods, the coil worked perfectly with
no arcs.  I think the coupling neared the optimal 0.095 for this coil.

I was a little worried since reviewing the flight tape yesterday suggested
that the coil was damaged buy the "odd sound".  The output decrease
instantly with the sound.  As it turned out, it was just corona spraying on
the back side of the coil.  There was no damage after all ;-))  That shrink
wrap is wonderful stuff!!  What IS that stuff anyway??

Earlier in the day, I had added a cap to my Tesla Coil Tuner (TCT) so it
could work with a low frequency coil like this and calibrated it with the
frequency counter function of the HP meter.  I could simply tune the coil
by raising or lowering the toroid on the brass all-thread rod.  So I tuned
the secondary about 5% low, which as I write this, I realize was incorrect
=:O  Arauugh!!!!  Should have been 5% high and the streamers would have
brought it down...  So the darn thing was about 10% out of tune >:-P


So we ran it off the variac slowly adding more and more power.  It easily
lit all the florescent lights in the room as shown here:

	http://hot-streamer-dot-com/temp/OLTC08-25-05.jpg

Soon, I had weaned it from the variac (and high power limiting resistor)
and it was running in it's full "low power" mode!  It was now a true
transformerless Tesla coil running as a 35 pound unit.  The controllers and
all worked perfectly!  The IGBTs were running at about 2500 amps.

Here is the schematic of the system:

	http://hot-streamer-dot-com/temp/OLTC08-25-02.gif

The sparks were a little short:

	http://hot-streamer-dot-com/temp/OLTC08-25-03.jpg
	
But there were sparks and a heck of a lot of "power" that filled the room.
I could kick myself now for screwing up the tuning thing but...  The heck
with it ;-))

The power of the coil was "ferocious".  None of the usual "let me touch it"
folks wanted to go near it :o)))

	http://hot-streamer-dot-com/temp/OLTC08-25-02.jpg

It was like burning the aluminum tape off and pitting the aluminum toroid
:-))  Seemed to have low voltage, but very high current, arcs.  I thought I
may have messed up the coil's output impedance, but now I think it was 10%
out of tune :-p

Here is some testing at full power (still, just off the weenie 120VAC...)

	http://hot-streamer-dot-com/temp/OLTC08-25-06.jpg

This is after we had optimized the dwell time with a wooden stick attached
to the controller dial.  It was really cool and had a giant blue glow that
the picture didn't capture well.  The arcs were about a foot and a half.
The dwell time was only 45uS and the arcs seemed "short", but with my darn
tuning error...

Here we are frying a Microsoft CD :-))

	http://hot-streamer-dot-com/temp/OLTC08-25-04.jpg

So there was a bad tuning error but all else went just fine.  The
controller did perfectly.  The IGBTs ran at 2500 amps just fine.  Messing
around with the dwell and all proved that the transorbes and all the
protection circuits work just fine.  Everything came home alive and well
:-))  If wee "could" have blow the electronics, they "would" have blown...
Sorry Marco, my dead IGBT bucket is still empty :o)))  Bill did not have
240VAC available (probably a good thing :o)) but at 120VAC the OLTC seemed
to run just fine.

Much to ponder... But not as much as it "could" have been :o)))

So, now, there is now doubt, the OLTC is born!!! :-))))))

Cheers,

	Terry