Re: OLTC update

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Terry,

On 20 Sep 2002, at 17:28, Tesla list wrote:

> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Hi All,
> 
> Although I have been a bit lazy lately ;-)  I still am working on the OLTC
> quite hard.  Much of the work right now is very time consuming trying
> models and stuff.  Pretty boring especially when the results are not
> significant...  Also been playing with streamer currents and such.  Also
> fixing blown fiber probes as a result ;-))
> 
> I decided not to pursue the cascade Marx configuration right now.  Seems
> just to complex and Ken points out some problems that would be messy to
> fix.  That configuration is very interesting indeed!  But too far different
> from what I have now.  It would need a multi turn primary and the caps
> would probably have to be charged through very large inductors or
> transistors.  Primary losses may also be a problem since fewer IGBTs and
> four in series now...
> 
> I am also holding off on the OLTC-2 effort until I can find out more about
> streamer loads.  Even though the losses are high right now, The early
> streamer data seems to suggest that it is not that terrible of a problem.
> So I am going to learn more before changing the configuration much.  I
> don't want to do a be redesign and find out I didn't accomplish much.  I
> was considering rewinding the secondary on a plastic form but the data say
> to wait for now till I really know what the benefits will be... 
> 
> The thing I am really excited about right now is I think I found a way to
> get rid of the iron core split 150mH inductor and increase power!!  By
> changing the inductor to an air core 34mH coil, I can run at 240BPS.
> Nothing else changes but the inductor.  The control circuit will
> automatically lock on at 240Hz and run just fine.  I need to use #20 wire
> to keep the resistance down but since I only need 34mH that is not a great
> problem now.  Many thanks to Richie Burnett for clueing me on to this!!
> This also eliminates saturation problems and gives very "nice" inductance
> properties.
> 
> The schematic is at:
> 
> http://hot-streamer-dot-com/temp/OLTC09-20-01.gif
> 
> The charging waveform looks like it did before but now I have an extra
> smaller bang between them:
> 
> http://hot-streamer-dot-com/temp/OLTC09-20-02.gif 
> 
> The current is nicely balanced still:
> 
> http://hot-streamer-dot-com/temp/OLTC09-20-03.gif
> 
> The line current gets strange now but it won't hurt anything.  So hopefully
> I will get more power, 10 pounds lighter, and simpler (no split inductor
> just a coil of wire now).  All for free basically ;-))
> 
> So I'll order up a 1000 feet of #18 wire (and a few miles of #26 in case I
> redo the secondary)and get it going at 240 BPS.
> 
> I am interested if anyone has any tips on how to wind a 34mH air core
> inductor with #20 wire using the least amount of wire (least resistance).
> I figure a very short large diameter coil?

The highest inductance per length of wire is scored with highest 
coupling between all turns. Therefore, a multi-layer coil with the 
number of layers = number of turns per layer is the way to go.

Regards,
Malcolm