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Re: [TCML] LTR/STR and spark length
Just thought I'd share my little coil with you since it's similar (4" x
20" these days) and uses a supply voltage about 10.6kV at 200mA
(modified 12/60 NST), so similar to your power supply. I'm also running
a static gap on this coil. Early on and in the pics below I have had
some primary strikes but hardly get those any longer. In the pics (at
the link below), the coil ran with a rather tight coupling. Some months
later after these pics, I ended up catching the bottom of the secondary
on fire (bottom turns shorted). When I realized the glowing red spots, I
decided to just continue and let disaster happen (which did). I ended up
removing about 1/2" of winding which also lowered coupling. The coil
these days is painted red, but nothing else has changed other than a
slightly looser coupling. No more problems with the sec bottom turns.
This coil has also ran very long runs (which I did mainly to verify
coupling was good for it's duration and I was curious as to how
everything would do over a long duration). I was happily surprised.
Well, I just wanted to show why I think your coil could probably do
better than it is now. BTW, the MMC is 18.8nF, so I also am running STR
with this setup. Other than maybe the gap and toroid, our coils are
probably not that different. Also, on this coil, I typically run about
90 to 100 volt input via a variac to keep sparks out of harms way.
With a 9/180 supply, you should be doing much better than 18" sparks.
I have to assume spark gap losses are a large reason why you are not.
I don't know any details of your static gap but I have to assume it's
running an extremely high bps as the gap is set narrow to due the 9kV
The sphere should have done better than the small toroid you
described. But, a larger toroid in the 5" x 20" range would double the
top capacitance beyond that of the sphere and also add a couple more
turns on the primary and do even better. It would be nice if you could
upgrade the cap bank to 70 or 80nF and run LTR. You might want to
start heading towards an SRSG upgrade if you can get a cap size up
there. Both cap and rsg upgrades can get expensive and I know it's
easier said than done.
The larger secondary looks real nice! This should be a nice coil but
it will require all new components and all the same upgrades.
Neal Namowicz wrote:
First, I'd like to thank Gary Lau on the previous advice you gave me
re: resonance and capacitance. If you'll recall, I started out with a
2nf cap bank, bumped it up to 4, and then after I was told that was
significantly str I managed to bump it up to 25 nf. (I had more caps
laying around than I realized). Here's my question- how much is one's
potential spark length limited by the height of the secondary? Here's
basically what I have; 4" x 18" secondary, flat spiral primary using
.25" cu tube, and I changed to a 9kv, 180ma power supply. I've tried
various toploads, and I've found that I'm still partial to the sphere
shape. I tried a dryer duct toroid that ended up being just slightly
wider than the secondary is high, and had good arcs breaking out all
over at 18"+ . Then I went back to a 10" sphere with a 12" brass rod
stuck into a hole in the sphere. I'm getting easy 18 to 20" streamers
off the top. Given that I'd like to stick to my quenched single
static gap (for now, at least), can I expect to get any better, or is
it time to "upgrade" to a bigger secondary? A long time ago I started
a bigger coil, but didn't get any farther than winding the secondary
(8"x48", wound with 18 ga). Thanks everyone, for your help and input.
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