Re: Desktop Bipolar Coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Yes, Antonio's correct. The term overcoupling with TC's is in several years 
of postings and probably website write-ups. We're probably stuck with this 
incorrect and often misunderstood term.

In any event, the term (overcoupling) used with TC's and performance 
problems has to do with the percentage of electromagnetic interaction 
between coils adjusted too high and results in unwanted racing sparks from 
the secondary winding instead of the top terminal. The voltage gradient is 
too high somewhere along the secondary and enough to cause breakout form 
the secondary winding (in my experience, at or near the top).

Tighter coupling is great up until those pesky breakout problems begin. 
That is the point of "overcoupling" which has been used here (incorrectly) 
for so long. And yes, performance will bite the bullet as soon as that turn 
opens or shorts.

Take care,
Bart

Tesla list wrote:

>Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
>
>Tesla list wrote:
> >
> > Original poster: "Stephen Conner by way of Terry Fritz 
> <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
>
> > >I've seen many bipolar coils many of which have overcoupling on both
> > >secondarys which will result in a shorter spark length than optimum
> > >performance would
> >
> > Can overcoupling really make performance fall off? In my own (limited)
> > experience I've only ever found that the tighter the coupling the better it
> > works.
>
>The most that can happen is a very slight drop in performance if the
>coupling coefficient happens to be between two of the optimum values.
>But this is only observable without instruments when the coupling
>coefficient is above 0.28 or so. There is a significant dip between
>0.6 and 0.38 and another smaller between 0.38 and 0.28. But usual
>Tesla coils operate with significantly lower coupling, and in that
>range what dominates is the smaller losses that result from higher
>coupling. There is nothing that can be called "overcoupling" in a
>normal Tesla coil. This term is used in doubly tuned bandpass filters,
>and is characterized by a frequency response with two peaks instead
>of just one (the also so called "frequency splitting").
>But these filters are far more lossy than the worst of Tesla coils,
>that are always very deep in the "overcoupled" region, and so
>the quoted terms above, in their normal sense, don't apply.
>
>Antonio Carlos M. de Queiroz
>
>
>
>