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Re: [TCML] LTR/STR and spark length



Hi Neal,

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.

http://www.classictesla.com/photos/ba45/ba45.html

Take care,
Bart

bartb wrote:
Hi Neal,

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 output.

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.

Take care,
Bart

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.

Neal.
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