Re: 8" coil :(

[Terry Fritz <twftesla-at-uswest-dot-net>]

Hi Chris

At 11:53 AM 7/20/00 -0600, you wrote:
>The data on Chris' coil:
>
>Sec: 8" wound 29" with 20 ga

First we can find the inductance of the secondary coil which is really
important.  20ga. magnet wire is very close to 29.4 turns per inch.  So you
have 853 turns of wire.  Using the standard formula's like the ones at
Matt's site (Helical Coil Inductance)...

http://home.earthlink-dot-net/~electronxlc/formulas.html

You can calculate the inductance of the secondary coil very accurately as
35.71mH.

E-Tesla5 will find the resonant frequency:

http://users.better-dot-org/tfritz/site/programs/programs.html

Guessing at a few dimensions, I get 143.9kHz as your system resonant
frequency.  You can use the formulas (Archimedes Spiral Coil Inductance) to
find the tap point.  I used my "TeslaPro" program at the above site which
is not the best in the world but it is mine so "i" like it :-))

With a 0.035uF cap you want a primary inductance of 34.87uH which will be
at 8.03 turns.
With a 0.045uF cap you want 27.14uH so tap it at 7.06 turns.
Using the "Resonant Circuit Formula".

You will have to probably add a 1/2 turn or so to make up for steamer
loading.  A little adjustment is always needed from these numbers to get
the best streamers.

Your coupling is about 0.18 which should be fine.  If you get racing arcs,
raise the secondary and inch or so to reduce the coupling.

I'll leave adjusting the pig power, gap, and such to those that have more
experience than I with that.

Cheers,

	Terry






>primary: 1/4" copper 1/2" c-c turn spacing, 11" ID 12 turns ( I had it tapped 
>at the outermost turn)
>bottom winding of sec is 3/4" below bottom of pri.
>cap: .035uF -at- 20kv Mica pulse.....045 with my plasticcapacitors cap
>60bps sync gap, which is very clearly out of phase, so that needs to be 
>addressed. 
>topload is 6 x 24" toroid
>
>I wish there was some low power, non "violent" way to adjust the phase. I 
>really don't like to have my safety gaps firing like that. I'm not willing to 
>widen them yet, though, as the caps may not handle the overvoltage...that 
>remains to be seen.
>
>It is pig powered. I started at 1500 watts, which wasn't enough, and so I 
>added an NST as additional ballast, whoch added about 400 watts to the pig, 
>and did indeed help matters, so I think is is really a matter of enough power 
>to drive this coil. I think between 3 and 4 kVA is where this is going, but I 
>can't get that right now. THanks for any ideas!
>
>Chris
>