OLTC - Primer

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

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

Hi All,

Since I am doing just "busy work" on the coil that is not too interesting,
I thought I would put together a little primer on the whole OLTC thing.

Here is the "basic" diagram of the Off-Line Tesla Coil (OLTC):

http://hot-streamer-dot-com/temp/OLTC8-14-01.gif

There is really very little to it.  No variacs and no high voltage
transformers.  Thus, it is very light weight.

It plugs into your 240 VAC dryer outlet.  Basically, the AC voltage is
rectified by a simple beefy bridge rectifier ($4 from DigiKey) through an
inductor to charge a 47uF cap.  The cap is actually ten 4.7uF 600V caps
that look much like the Geek group's MMC caps).  Ten IGBTs act as the spark
gap:

http://hot-streamer-dot-com/temp/P8050015.jpg

Little heat, no sound, no light...  I think it will dissipate about 30
watts.  About 400 watts less then a normal gap ;-)

The primary is actually a single turn at only 500nH (0.5uH).  Very low
inductance and very low resistance (loss):

http://hot-streamer-dot-com/temp/P8060019.jpg

The secondary is a very high inductance (600mH coil) made from #28 wire.
It is not made yet but will look much like the secondary in this photo
(note the more complete primary too):

http://hot-streamer-dot-com/temp/P8100020.jpg

The IGBT controller is an electronic circuit the monitors the current to
the cap and decides when and how long to run the IGBTs.  I looks like this:

http://hot-streamer-dot-com/temp/OLTC-PowerContFront.jpg

http://hot-streamer-dot-com/temp/OLTCigbtC-8-12-03.jpg

Just a hand full of parts plugged into a protoboard.

http://hot-streamer-dot-com/temp/OLTCigbtC-8-13-03.gif

Your done!  That is all there is to the thing!!

Just a rectifier, inductor, cap, primary, IGBT array, electronic
controller, secondary, top load...  and you have a coil!  Very simple (but
very "different" in theory).  This is what I am trying to do.  It is not
built yet and the thing has never been demonstrated to actually work in any
form.  It's all just theory and computer models ;-))

However, it is taking shape fast ;-)  Here is the bridge rectifier part
with fuses and other general power control "stuff" to connect the 240VAC to
the coil:

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

The MOVs have to be about 700 volt types rather than 240 volt ones as
modeling has showed.

I have been spending a lot of time with computer models like:

http://hot-streamer-dot-com/temp/OLTCigbtC-8-13-01.gif

But I have a lot of stuff on order and coming in so it should be taking
shape fast :-))

Will be spending time on the IGBT array and inductor next.  Maybe this will
help bring some folk up to speed on this whole thing ;-)

Cheers,

	Terry