Re: Directions for tesla coil research

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Rob,

On 5 May 2002, at 20:47, Tesla list wrote:

> Original poster: "rob by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<rob-at-pythonemproject-dot-com>
> 
> Tesla list wrote:
> > 
> > Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <scepp-at-mts-dot-net>
> > 
> > Question about increasing Q, See below,
> > 
> > ----- Original Message -----
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > To: <tesla-at-pupman-dot-com>
> > Sent: Sunday, May 05, 2002 6:44 PM
> > Subject: Re: Directions for tesla coil research
> > 
> > > Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <evp-at-pacbell-dot-net>
> > >
> > > Tesla list wrote:
> > > >
> > > > Original poster: "Malcolm Watts by way of Terry Fritz
> > > <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> > > >
> > > > HI Paul, Jim,
> > > >
> > > > On 3 May 2002, at 10:41, Tesla list wrote:
> > > >
> > > > > Original poster: "Paul Nicholson by way of Terry Fritz
> > > > <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> > > > >
> > > > > Jim's comments cut to the heart of the matter:  The question is,
> > > > > what is the relative significance of topload voltage and topload
> > > > > charge in determining streamer performance?
> > > >
> > > > Absolutely agree. It's been a hobby horse of mine for quite a while
> > > > now. For one of my coils, increasing Ctop by an effective 100% (Ctot
> > > > increased from about 26pF to 33pF or so) resulted in a 25% increase
> > > > in reach with the same primary energy and breakrate. However,
> > > > unloaded primary Q was also increased by 50% as a result of retuning
> > > > so the Ctop factor did not sit alone. Given half a chance (like a
> > > > suitable test room), I'd like to boost Ctop further and check for
> > > > further improvement. Maybe in the semester break in June.
> > > >
> > > > Regards,
> > > > malcolm
> > >
> > > I've long suspected that the beneficial effect of big topload
> > > capacitance is to reduce the L/C ratio of the secondary, thereby
> > > lowering the resonant frequency and increasing the Q for the same
> > > streamer loading.  Result is there should be more energy stored before
> > > breakout, and coupling should be easier to adjust.
> > >
> > > Ed
> > >
> > 
> > How does a bigger top load increase Q.    if Q = Xl / R      and     Xl  =
> > 2 * pi * f * l.
> > 
> > from these equations, one would assume that if frequency goes down, due
to a
> > shift in resonant frequency, then Q decrease because Xl decrease.  I know
> > I'm missing something important here, right?
> > 
> > Shaun Epp
> 
> Perhaps is a conservation of energy thing.  A bigger top cap can store
> more energy without it leaking away in small streamers.  Then when the
> energy builds up high enough, you get the big bang :)  It is definitely
> true with my tiny 2Mhz test coil.  With no top cap on the pvc pipe, I
> don't get much streaming out of it.  Plus it raises the freq up beyond
> where my MosFET circuit can efficiently drive the coil. Rob.

In some cases that would definitely be true. In the case I cited 
however, while Ctop was increased, the minimum radius of curvature of 
the terminal was maintained (if not decreased somewhat due to the 
less smooth surface on the larger topload).

Regards,
malcolm