OLTC update

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

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

Hi All,

I have been working pretty hard on my Off-Line Tesla Coil project.  Mostly
ordering things and running computer models to check things out.  But I am
starting to get some "real" stuff going too ;-)  All still looks well...

I built the 240VAC controller today.

	http://hot-streamer-dot-com/temp/OLTCcontFRONT.jpg

	http://hot-streamer-dot-com/temp/OLTCcontBACK.jpg

	http://hot-streamer-dot-com/temp/OLTCcontSCHEM.gif

	http://hot-streamer-dot-com/temp/OLTCcontTOP1.jpg

	http://hot-streamer-dot-com/temp/OLTCcontTOP2.jpg

It came in at 4 pounds 15 ounces instead of two pounds ;-))  Hey, that is
still lighter than just a big variac knob like you "big iron" guys use
:o)))  It is designed for about 1+kVA but it could do about 4kVA if it had
to.  All heavy duty stuff that can take a big "hit" if things go...
"bad"...  Really not much to it.  Just a nice safe way to control 240 VAC
into a Tesla coil.  I have not had a chance to test it yet since the dryer
outlet is being used for the stupid dryer ;-))  I got to use the Brother
P-Touch label maker a lot :-))

I am also collecting parts for the IGBT switch:

	http://hot-streamer-dot-com/temp/P8040005.jpg

I guess it does not look like much yet :-)  Actually, only the 10 IGBTs in
the tube, the bag of MOVs, and the section of heat sink I sliced out right
quick in the band saw are for the IGBT spark gap.  The box and protoboard
are for the IGBT firing control.  Hopefully it will look cool pretty soon
;-)  I was going to get the milling machine working on the heat sink
tonight, but getting too late...

I found that I need to fire all the IGBTs within 1.3uS of each other.  Dave
Sharpe clued me into the Toshiba TLP250 driver chip (just another DigiKey
part...) which will be great!  I still need to work a lot on the SYNC
timing stuff...  The IGBTs will be paralleled together with less than 15nH
of inductance.  More than that and their phase angles start to get goofy.
It is really very simple in practice...  I guy at work gave me a big beat
up 300 amp brick but I was surprised it was rated at "only" 600 amps peak :-p 

Seems the big bricks are not designed well for really high peak currents
like my project will need.  No matter, since many small IGBTs are like
1/10th the cost...  I wonder if an extreme Tesla coil use of IGBTs will
teach the "big boys" a few trick like the MMC caps did ;-))  The bricks are
really not designed all that well...  they are mostly worried with slow
speed high thermal dissipation stuff...

I think I will go with a primary coil of three 14 inch diameter copper
tubing loops (1/2 inch diameter tubing) spaced 2.5 inches apart.  Everyone
can find this "stuff" and the IGBTs can evenly push current into such a
structure.  Tuning will probably be through a variable number if primary
caps.  Might need a multi-taped resonant inductor too, but I'll see...  A
lot depends on the inductance of the cap and switch structures...  Maybe I
can have an adjustable inductor in there somehow...  Talking like 300nH...
Still thinking...  It is all brand new territory here...

OLTCs are sort of complex from a theoretical point of view, but the
hardware is really very very simple once the gnarly details are figured
out.  Hopefully, it might actually work!!  I am trying to keep it really
simple so others could easily make one.  There are fancy improvements and
stuff I am neglecting in the name of "keep it simple"...

We will see....

Cheers,

	Terry