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Re: Getting back into coiling

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

At 06:14 AM 5/16/2005, you wrote:

HI All,
I have been collecting transformers and tubes and stuff in hopes of getting back into building a coil.
I have also been reading through my copies of John Coulter's books which now seem to be a little out dated.
I have a couple of questions, to start out with, that I have not been able to find adequate explanations in text
or on the web and I hope one of you could give me a site or an explanation. Although I have two degrees in EE I and
work with high powered radar systems, I have embarrassing little knowledge in Tesla theory. 

Interesting, I think Dan and Ed are also radar guys...  Here is a nice site:

http://www.richieburnett.co.uk/tesla.shtml

Don't worry, you will catch on very fast!


1) My first and only coil was a simple spark gap. I have been reading about the rotaries but am slightly confused.
Are these just used for pole pigs? 

Nowadays, synchronous gaps are used very well with NSTs and larger capacitors:

http://www.richieburnett.co.uk/indkick.html#kick

They are generally known as LTR coils since the primary capacitor is larger than is used in the resonant case. The precise timing of the sync gap allows larger capacitors to be used and proportionally larger output.

I have read implications that they are used with NSTs. If so does the motor have
to be synchronous? 

Yes!

I would assume so or is it the capacitor that just stores the energy within each cycle. If this is all
still good then does the motor have to be timed so that the breaks occur at the optimum point within each cycle? 

Yes, there is a "sweet spot" in the timing normally found by trial and error.


2) Could someone explain in simpler terms the relationship between the length of the spark gap and how it effects the coil tuning and
ultimately the bolt emissions?

The spark gap does not affect tuning. If it is just a static gap, than the gap should be set to fire at the NSTs maximum voltage. That charges the primary cap to the maximum voltage for firing with the most energy.


3) Is there a good site that explains the process of tuning the primary and secondary circuits? I have read that, at least for the primary, tuning is
done unpowered. That is as much as I know. 

The primary circuit is just an LC     Fo = 1/ (2 x pi * sqrt(L C))

The secondary is also lust an LC but the C is a bit trick to find

The secondary has the inductance of the coil and the natural capacitance of the coil (Medhurst Capacitance) plus the capacitance of the top terminal. The coil's capacitance and the top load capacitance can be calculated using finite element programs that find it based on the physical dimensions:

http://hot-streamer.com/andrewb/

But this nice big program sort of does it all!!

http://www.classictesla.com/java/javatc.html

If you have the test equipment available you can just measure it too. There was a website that had a nice explanation of how to do that but "I" don't know it right off...


I apologize for the sophomoric questions but I would like to start my next coil with as information as I can gather.

No Problem ;-) None of use are born knowing this stuff and it is not a normal thing you find in school ;-)) I think you will happy to find however that there is some really good science behind it all nowadays!

Here are some handy and very well tested formulas too:

http://web.archive.org/web/20040308060705/http://home.earthlink.net/~electronxlc/formulas.html

Cheers,

        Terry