OLTC update - A problem!

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

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

Hi All,

I retuned the coupling and all

http://hot-streamer-dot-com/temp/OLTC08-28-08.gif

on the OLTC and the performance was better but still not as I had hoped.  I
think I know why now.

Using the output impedance calculation method at:

http://hot-streamer-dot-com/TeslaCoils/Misc/impedance/impedance.html

I came up with an output impedance for my coil of 2,044,989 ohms!!  That is
really high!  My big coil is only 26500 ohms.  So I think the coil's output
impedance is too high to fry nitrogen the way we would like it too.

Output impedance is governed by the Lsec and Csec ratio.  So I think I need
a smaller secondary L and a top terminal the size of a cow or something...
I'll have to work on this...  I was worried about this, but I didn't think
I would make it this far so soon :o))  I suspect this problem plagues most
low frequency coils.  I was modeling the coil to run into a 220KOhm + 2pF
streamer load which has a magnitude of 2,191,278 ohms so it "should" have
worked from that point of view.  Source and load "should" have been closely
matched.  But it looks like there are a few unknowns still out there ;-)
With 286 watts in I should be able to get streamers of 28 inches according
to John's formula.  Much more considering I am not burning power in a spark
gap.  But either the low frequency (I note that I am at the frequency of
Greg Leyh's Electrum which seems to come in a little low for streamer
length given the input power) or the impedance thing is causing a problem.
Probably time to get out them fiber-optic probes ;-))


In other news...  I designed in IGBT current tester.  Here is the simple
diagram:

http://hot-streamer-dot-com/temp/OLTC08-28-06.gif

Here is the messy one:

http://hot-streamer-dot-com/temp/OLTC08-28-07.gif

It is basically a copy of a single section of the coil.  I played the
values to get an almost perfect matching current waveform to the real one
but I can push 600 peak amps here on a single IGBT (1200 amps with a slight
modification!).  I will probably use the coil's drive modules to run it but
making another drive circuit is pretty easy too.  With this tester I can
run the IGBTs until they break and determine how hard I can push them.
apparently nobody knows how hard IGBTs can be pushed in such case.  Be
interesting to see :-))

The impedance problem is the first real "obnoxious" problem with the OLTC.
But it is not a mater if an OLTC works now but rather how to perfect it ;-))


BTW - For 50 Hz UK operation. the charging inductor needs to be:

50 = 1 / (2 x pi x SQRT (47e-6 x L))  Where L = 215.6mH    Big ~6 to 10
pound split core (E-core may be better)) that does not saturate given the
current.  I guess it could be designed for a saturable reactor if one were
really good at that stuff...

You need to watch that the peak value of the primary voltage does not go
too high with the longer charging time and the line voltage you have over
there.  I can't think of anything else that would be affected.  I am not
sure my IGBTs can take 240VAC yet until I do the destructive testing...
The IGBTs and stuff will be here Friday so I can do that this weekend.


I should point out that this OLTC stuff is all brand new bleeding edge
stuff and I am using a ton and a half of computer models and extravagant
test equipment to get it to work.  The goal is to make it very simple and
easy, but right now the guarantees are zero for those that wish to try it
themselves.  Things have gone extremely well, but if you try it and have
trouble right now, just don't blame me :o)))

Cheers,

	Terry