Re: OLTC

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

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

Hi David,

At 09:16 AM 8/10/2002 -0400, you wrote:
>
>Hey Terry,
>
>I'm going to have to show my ignorance and ask what the "OL"
>in OLTC stands for? I have started following this thread with in-
>terest but can't recall what the "OL" stands for for :-/
>
>David Rieben
>

No worries, if this works, that question may get asked again someday :o))))

It stands for "Off-Line".  This coil runs right 'off line' voltage AC
without step up transformers.  The primary circuit is not 10,000 to 20,000
volts like in a conventional coil but rather about 500 volts resonated up
from the 240 VAC line voltage.

http://hot-streamer-dot-com/temp/OLTC8-8-01.gif

(BTW - I think hot-streamer-dot-com will be working much better now ;-)) 

In this diagram (a littles sketchy I guess, prolly should make a nice
one...) the top two circles are the AC line voltage like from a dryer
outlet.  120 - 0 - 120 split single phase. That voltage is simply rectified
with a bridge rectifier and feed through the inductors to C7 which is the
main primary cap.  It is like 28uF in this case since the voltage is only
about 500 volts.  The switch in the lower left is an IGBT array in real
life that can switch the 500 volts with very low loss (2500 amps!).  The
rest of the coil is conventional but the primary is only a single big turn
and the secondary has many more turns since the operating frequency is lower.

This shows the main waveforms:

http://hot-streamer-dot-com/temp/OLTC-08-07-1.gif

The green is the AC from the rectifiers, the red is the voltage on the main
cap, and the blue is 100X the charging current.

The advantage is that there are no transformers, variacs, PFC caps...  I am
trying to get the entire system (control cabinet, and coil, to weigh very
little, like 30 pounds) The main gap is solid state and eliminates the
giant loss of a conventional spark gap.  Therefor, if this coil has 700
watts input, that is easily equivalent to a 1kW+ conventional coil.  If the
power is scaled up, there is very little additional weight.  I think such a
system could do 7 foot arcs if the cap and IGBT array are beefed up to take
about 5000 amps peak.  But that is all one would have to do.  There really
is just not much "stuff" to such a coil and the theory is actually simpler
but "new".

Right now, it is just all theory and computer models but I am trying to
build it up to see if it really works.  It really "has" to work.  It just a
matter of getting components to do what the models says they have to do.
Modern caps and IGBTs seem to be very capable of the task. 

I should make a nice web page and explain all the details in a nice format.
 But I could spend my time doing that or building the coil.  So... this is
all you get :o))  I have kept and reported all the details to the list if
you sort for posts beginning with "OLTC". 

BTW - Some of us remember the days when people said computers could never
predict a Tesla coil's functioning (and you know who you are! :o)))).  Now
it seems we can't build Tesla coils without them ;-))  LTR coils were first
predicted by computer, but we would have figured it out fairly quickly
without them.  Computers certainly figured out the best component values
for them far faster than say "trial and error..."  However, this OLTC thing
would have been virtually impossible to "whip up" without a LOT of computer
power.  There are some pretty tight regions it needs to work in and specs
it has to meet to operate.  One could never figure out how to get every
thing to "sing" together without lots of study by computer.  Also, many of
the ideas that make it work, where from others here on the list.  I sort of
had the idea, but great ideas from many people could be quickly gathered
here that really provided the set of keys to make it run.  On-line data
sheets and parts ordering saves a few months too :-))

If this works, it will truly be a modern state of the art Tesla coil that
will be very new and different.  It may also be far better in many ways.
If we can get it at 30 pounds, keep it simple, $400, and seven foot
sparks...  It would "change things"...  

Cheers,

	Terry