Jeremy,
I built a primary out of two strips of brass ribbon and one strip of copper in between and it was really bad, not to mention very expensive.It worked but it was difficult to tune and the output wasn't that great. You also have more to worry about with turn to turn arcing. I didn't see any corona but I'm sure a time exposure would have shown a lot and I didn't think of that at the time. I'll post a picture later when I am at home. Maybe if you encase the whole thing in epoxy will you get rid of the corona but good luck tuning it. :)--- On Mon, 7/28/08, DC Cox <resonance@xxxxxxxxxxxx> wrote:
Not sure I follow with "two strips of brass ribbon and one strip of copper in between" ?.. some things to watch out for is your cap bank must be able to maintain the load also. My primary at just 10mR would set a figure of 200amps to 800amps. So chances are you would have to retune and add a larger toroid to lower the frequency to match.
A lot of caps maybe only capable of 10-50amp pulses, in general most coils would have problems with less than 5 turns.. by the time you get to 3turns your getting into KA pulses. As resistance goes down current pulses will rise, as inductance goes up, so does resistance, but the inductance will lower the current pulse also.
It can get pretty complex when you sit down and crunch all the figures. I think anything over 5 turns cap banks should be happy with, then resistance is not much of an issue. To keep a happy balance, if you add more turns for much inductance (which limits the current pulse) then increase the dia of the pipe to prevent resistance losses going up also.
Resistance is a real problem for me in my design.. I wanted to increase the inductance to limit the current pulse ( cap bank sux) and then in doing so the resistance goes up which also limits the current pulse and increases losses. So I resorted to 2" wide strap which now gives 6uH ( 4 turns) at 0.002ohm. which at about 50VDC input is 250amps.
Resistance isn't as much of an issue when you get into KV ranges. Though I still like to get the best out of everything. I favour strap over pipe, though of course there is nothing wrong with pipe, I have used it for a great number of years. Though when you start to push every inch of efficiency out of the coil then you start to think about things a lot more.. a small increase in efficiency here and there over a lot of elements can add up!
A lot of coils have all become "in general" in design.. in general it was 5-10 turns ? overall it works out well, but why not use 3 turns or less ? if your primary pulse 5KA with 1 turn and your caps can only deliver 10amps, then 1 turn , or even 3 turns will not work as well as 5 turns or more.. Increase your cap "quality", we now have high DVDT/DVDI caps so now we can start to explore more like 3 turns... the problem is so many people using so many different parts, what works for one, may not work for another.
Build 2 identical coils, only different the number of turns on the primary and the cap back pulse ratings.. one coil could work 50% better than the other... As said before, no use trying to pull KA's from a 10amp cap bank. Use "poor caps" use 10 turns, use "good caps" 5 turns.. the list of configurations is endless. This is why things get generalised as 5-10 turns, as in general most cap banks can uphold 10-50amps.. has worked fine for the last 50 years or more ? Though if you cap bank can deliver KA pulses then why not use ?
Its not however as simple as that, someone is going to say pushing more current across the gap will make it harder to quench.. so again its why things get done in general... overall there is no 100% perfect design... design "in general" and in general get good results... however with some thought and a little bit of thinking things can be made much better......I think my first primary used 15-20 turns, I could never get anything to work better than that until I built my own cap bank, progressed to 3 turns and it doubled the efficiency... does not mean that if someone else did the same that it would work as well.. always other factors to take into account... Like another poster said someone could use copper pipe and change to strap and it not work, another person could change and it could work a lot better... Unfortunately you cannot just alter one thing and expect it to work better.
my 2c worth... Chris _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla