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Re: [TCML] For the SISG experienced out there
Hi Phil,
Thanks for the great advice. For DC charging in the past, I also used a
series of diodes, but thought I would just go the route of some hv
diodes to keep construction easy. I'll be using 15kV diodes, but it
sounds like it might be wise to double up and series 2 per bridge leg.
Unless I do a voltage doubler or something, the 6 boards sounds like out
of the question for the NST. So, the topology for firing a series of
boards is per the 300V Sidac's at 3600V per board, so 3600V x 6 boards =
21.6 kV. It looks like for the 11 kV NST = 4 boards. 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.
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). 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 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. That coil is mostly done and maybe I
should stick to that plan. If I use the 4 boards, I planned on the NST
mentioned with my smaller 4.5"D coil. As you can see, I'm totally unsure
if I should use existing coils or wind a new coil altogether for the
sisg. So, if there are some "coil LC preferences", then that would
likely dictate a new coil.
Oh, the NST was a 12/60, after removing some windings and shunts, 11/200
(nothing special, but it sure can dance).
Take care,
Bart
FIFTYGUY@xxxxxxx wrote:
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
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