Re: [TCML] For the SISG experienced out there

[FIFTYGUY@xxxxxxx]

In a message dated 5/8/08 9:18:54 P.M. Eastern Daylight Time,  
bartb@xxxxxxxxxxxxxxxx writes:

>Now, if I use my 14.4kV pig, a little over 5 boards. Maybe, I  should just 
settle on 5 to 

>make it easy and keep 1 board as a spare.



I'm using 6 boards with my 14.4kV pig, but I'm  also running it through a 
home-made stack of 2 paralleled 20A+ variacs on each  leg (4 total variacs ganged 
on 1 shaft). I'm using a homemade fixed ballast  choke as well to limit the 
pig current to 60A. Haven't tripped the 50A breaker  feeding my control box 
yet. But I can put 280V into the pig to get the voltage  out for 6 SISG4 boards 
to work. 
    It's weird to ramp up the variac until all hell  breaks loose. It sounds 
nice and smooth, like a synch gap, at the "breakover"  point. About 30A draw 
with .150 uF primary cap. Cranking just a bit more, and  up to the max on the 
variacs, suddenly gives the streamers a mean, obnoxious,  metallic ringing 
tone, and makes the streamers dart out much more chaotically  (doesn't seem to 
support sustained arcs as well). The Pig current draw maxes  as well. 
    It would be nice if you could do some breakrate  measurements with your 
setup and verify that the bps is going through the roof  when this happens. 
Probably not good for the SISG (or the primary caps!).  Maybe if we were clever 
we could find a way to pulse this voltage in, but  sustain the streamer with a 
normal rate. Only seems to make a 15% increase in  streamer length, but boy 
does it look angry!
 
>Are there any coil specific issues? For example, can I use a standard  

>8.5" x 40" coil with 9"x30" spun toroid? This coil is a bit lossy  (wound 

>with 24 awg at 1790 turns). 
 
    With a 6" coil, I had to eliminate my strike rail  or the secondary would 
arc to it (from a bunch of points from halfway up to  the top). The SISG 
doesn't seem to care one bit about primary strikes. But I'm  so overpowering the 
6" coil that the secondary streamers are reaching around  under the primary and 
killing electronics under there. Maybe put everything  under the primary in a 
big steel box, like Bunnikiller does with his 30kV pig  coil!
    See my next post for a simpler solution that I  tried and works really 
well!
 
>Are there any preferences for cap sizes? If 

>I use the pig, I'll likely go with my 60kV pulse caps at 0.06uF tank  size.


My understanding is that primary current over  800A is lossy through the 
IGBTs. They really start to heat up if you push  things past the "breakover" point 
or jack up the primary current too much. I  set another board on fire a few 
weeks ago, and I chalk *that* failure up to  overheating. 

>My original plan (bought the 6 pcbs from Mark about a year ago)  was to 

>use 4 boards for an sisg coil and 2 boards to power my attempt at  

>Tesla's flat coil at 1/2 scale.
 
    I'm making a twin 6" setup with two SISG4 boards.  I'm trying to be 
conservative on the design.
 
> So, if there are some "coil LC preferences", then that would  likely 
dictate a new coil.


I think keeping it around 130kHz and 800A peak on  the primary would make the 
SISG happy. Nobody has reliable data yet on how to  "tweak" the resistances 
for performance, efficiency, or longevity. Might want  an to at least do some 
temp monitoring on the heatsinks to see what works.  
I haven't been scientific in my approach, just  fooling around trying to 
break the darn thing!
 
-Phil LaBudde



Center for the Advanced Study of Ballistic  Improbabilities



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