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Powering up an SGTC

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Shaun

Fri May 11 2007, 03:08AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

So I just finished my first coil about 2 weeks ago, and I'm ecstatic that it works with 18 inch streamers from the topload.
I have not published its official stats and pics to the tesla coil list yet, but I will very soon.

Suffice to say that its powered by a 15 kV 30mA NST, with a 7.5 nF cap.
My big question is (and I'm knew at the beginning I would eventually end up here), how do I make it more POWERFUL!?
I have gathered that If I can get another NST in parallel, and double the cap value to compensate for quicker charge time, that should double my output power.

But a lot of little questions bug me, like should I try to get the same brand of NST? (Transco)
If I just add another cap in parallel to the one I have now, will it matter if they were constructed differently?
(The one I'm using is 7 parallel strings of 14 .015 uF in series, the spare is 12 .1 uF in series)
Am I missing anything important?

Sparrow338

Fri May 11 2007, 06:22AM

Registered Member #661 Joined: Sat Apr 21 2007, 03:17AM
Location: Ventura, CA
Posts: 41

Congrats on making your first coil! I'm glad to hear it's putting out. :)
Since I don't know what your setup there arn't many things I can think of that you can do to make it more powerful. However you can increase the spark gap distance, this will allow your caps to charge to a higher voltage thus dumping more power into your primary. You can also try increasing the size of your top load. Also might want to try a bigger tank cap. At the moment this is all I can think about without having more info. As for paralleling NSTs you probably don't need to do this since the NST you have has plenty of power. Although I don't know what size coil you have so maybe you do need more power. :) If it was me I would make sure you have two exactialy the same NSTs if your gonna parallel them, same output and manufacture.

Hazmatt_(The Underdog)

Fri May 11 2007, 10:03PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Increasing your spark gap distance...umm...yea.... that's probably not a very good idea. You're going to end up going over voltage on your transformer and burning out the windings when the LC tank rings down at 2X the input voltage.

No, rather what you need to do is start reading a lot of the Tesla Coil threads and do a lot of homework.
There are a few of us who have been doing a lot of reasearch on these systems and tuning out their efficiencies. Terry Fritz, Hot Streamer, the Tesla Coil Mailing List, myself, Both Steve's, Finn Hammer, and a lot of others contribute a lot of information, and what you really ought to do is the reading.

You will find pretty fast that 18" -24" is about as big as it gets for a 30mA transformer, and if you want more output you're going to have to push more current.

My systems would push 18" from 30mA transformers, and I'm getting ~40" from 60mA transformers, so you're definately in the ballpark. After that comes tuning for efficiency which is much more difficult and requires a lot of testing and some simulation.

Matt

...

Fri May 11 2007, 10:24PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

you should have no problems widening the spark gap, just makre sure that you have a safty gap somewhere that is set to fire at the NST's no load voltage (if you remove the tank circuit the safty gap should fire)

Coronafix

Fri May 11 2007, 11:47PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Yeh, there's no problem with opening the spark gap, as long as you've got a properly set safety gap.
When your spark gap starts firing during operation, then you know you've opened it up too much. This is of
course using a LTR cap bank, which you are.
How many primary turns have you got and where is it tapped at?
If tapped at the end you could add more turns and a bigger top load.
Bigger top load definitely increases streamer length but you need enough primary
to bring it back in tune.

Shaun

Mon May 14 2007, 08:05PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Okay, first of all, my primary is 13 turns total (30 deg inverse conical) tuned at around turn 11. The toroid is 4 in dia tube by 16 in wide. Sec is 20" winding of 24 ga wire on 4" thin-wall PVC. I have tried widening the primary gap, however past a certain point my safety gap begins firing AS MY MAIN GAP. This scared this living sh*t out of me when it happened cause my safety gap is mounted on the control board, about 8 inches from my hand on the variac wheel. It also worries me because it means I have an untold number of amps flowing through my filter inductor and other such things with much thinner wire (24 ga in filter inductors compared to 6 ga in capacitive discharge circuit).

I have done the reading, and instead of blowing the extra money on a second NST and another cap, I think I might try an equivalent sized DRSSTC. From what I've learned so far, these are capable of FAR greater arc length per watt, are much more controllable, quieter, and the parts under high stress (that break a lot) are less expensive to replace. Before I got Tesla Fever, I always used to have thoselow voltage electronics kits (with the breadboard and such), so I know my way around mildly complicated solid state circuits. It'll be a BIG challenge, I know. But as with all challenges, the harder you work the bigger the reward. :)

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