Re: Richie's Homepage and other topics

To: tesla-at-pupman-dot-com
Subject: Re: Richie's Homepage and other topics
From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sun, 12 Dec 1999 17:42:55 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Alan,
              Measuring resonator Q isn't a major problem. If you want 
an accurate figure for resonator comparisons, minimal output 
loading, great isolation of the resonator and a near-zero impedance 
base feed is required. Loading includes dangling scope probes near 
the coil. 
     Otherwise, measure the coil in situ to get the actual running 
figure (before breakout)..

> Original Poster: Alan Sharp <AlanSharp-at-compuserve-dot-com> 
> 
> Message text written by INTERNET:tesla-at-pupman-dot-com
> 
> Malcolm,
> I certainly with your comments on Richies web page.
> Thanks for the comments on my web page:
> >(1)     Mark Barton's 10kW flamethrower was definitely using IRF840 
> FETs. 
> This makes sense to me - Mark refered to irf540 in an email somewhere
> but these are 100V max compared to 500v for the irf 840. Do you have
> any other details of Marks "flamethrower"? (This was a 10kW Solid
> State Coil that produced a 3 foot wall of flame before the smoke came
> out)

He told me that the turns ratio in the driver was critical. I can't 
remember which way round it was  but having too many (few) turns 
in the primary prevented power going in and too few (many) resulted 
in smoke. The driver transformer had a closewound secondary with 
a wall of insulation and a primary wound along the outside so that k 
was in excess of 0.9. There isn't much more that I remember. Z 
matching does become critically important in CW operation and 
doesn't seem to matter for cap discharge operation.

> >(2)     Duane Bylund's use of DC resistance as a starting point for
> >matching a driver to a secondary could IMHO be bettered somewhat but
> >there is still a rider.  Firstly, a better match for the driver to a
> non-
> >sparking coil could be done by *accurately* measuring the Q of the
> >coil and deriving its ESR using  R = SQRT(L/C)/Q.  This figure is
> >considerably higher than the DC resistance of the coil in general and
> >should be good for direct coupling. For k < 1 this figure would be
> >higher. The rider: this figure would also be better for sparking
> >conditions (corona in particular) as the impedance at the base of the
> > secondary rises while the load impedance at the top reduces ( I have
> >measured this and infer that 1/4 wave transformer principles do apply
> >to the secondary - the base impedance swings about Zo^2 in accordance
> >with loading).  This is my opinion anyway. I measured this using link
> >coupling to the base of a resonator a few years ago.  Comments,
> >measured refutations welcomed.
> 
> That still leaves the problem of measuring the Q. I really now resort
> to making multitap output transformers. Good old suck it and see!

That's basically the approach Mark took I think.

> My page in at
> http://ourworld-dot-compuserve-dot-com/homepages/alansharp/
> 
> Alan Sharp (UK)

Regards,
Malcolm