Re: [TCML] For the SISG experienced out there

[FIFTYGUY@xxxxxxx]

In a message dated 5/7/08 10:32:31 P.M. Eastern Daylight Time,  
bartb@xxxxxxxxxxxxxxxx writes:

 
>Question: Has anyone ran an NST type transformer (shunts minimized)  into 

>an SISG setup (or beyond)? 
 
    I started with a non-modified Franceformer  15/60 before I kept cramming 
too much power into the 6" secondary. 
 
>I'm planning on basically an 11kV/200mA NST of which will be  rectified with 
15kV/540mA HV diodes >(full bridge configuration using 4  diodes).
 
    With a standard full-bridge rectifier, each  leg sees the peak voltage 
from the AC supply.  So with your 11kV AC NST,  each leg of the bridge will have 
to be rated at an absolute minimum of 11  kV * 1.414  = 15.6 kV. That's not 
counting all the "funny" stuff  from NST inductance, harmonics, static 
discharges, corona, and transients from  all the high-current discharges running 
around. Not to mention the biggest  killer of my rectifiers - direct secondary 
strikes!
    I made each leg of my bridge out of 40 1kV  1A diodes seriesed. These 
were fast-recovery (75nS) UF4007's, My thinking was  that their fast-recovery 
would block any RF from getting back to the power  supply. 
    I also put a 200 Ohm 100W resistor in each DC leg  off the bridge. I 
later replaced two legs with "bar" rectifiers that came from  a 3-phase rectifier 
for the HV power supply of an AM radio station. Two weeks  ago I killed one of 
those "bars" from a direct secondary strike. 
    I'm getting annoyed enough that my next move will  be to recycle the 
rectifier assys from my XRT, and protect everything with  a zillion TVS's...
 
>I'll be using 6 boards, so there will be some decent power to deal  with. 
I'm just curious if anyone's >been down this road that I'm traveling  and could 
offer any advice on high power 

>into the SISG.


    6 boards with 4 sections each will just sit there  and twiddle its thumbs 
until you hit 15.3 kV. Trust me, no current draw, no  sparks, no _nothing_ 
until the voltage across the 6 x SISG4 hits the nominal  21.6kV peak. I've got 
old-school amp and volt panel meters for the Pig primary,  and there's a magic 
point at which suddenly it all happens. Yes, disconcerting  when you're used 
to ramping up spark-gap coils! But you won't get any results  unless you use 17 
sections (4 and 1/4 boards), or 5 boards if you boost the NST  primary with a 
variac. 
    Remember, there's no resonant rise because the  rectifier is blocking it. 
Anything like level shifting or boosting it with a  choke would give you more 
voltage than you need, eh?
 
    BTW, where did you get an 11/200 NST??
 
-Phi LaBudde

Center for the Advanced Study of Ballistic  Improbabilities



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