From: "Malcolm Watts"
Date: Fri, 18 May 2001 10:53:11 +1200
Subject: Re: [TSSP] Measured vs. Operating coil coupling?
Hi Paul,
There's no doubt in my mind where a spun toriod lies
(leaving oxide layers aside):
On 17 May 01, at 18:25, Paul wrote:
> Hi Terry, All,
>
> Terrell W. Fritz wrote:
>
> > ...Dryer duct toroid tend to have strangely poorer performance
> > than smooth toroid. Perhaps this is a truly new concern for
> > toroid builders!
>
> It would be interesting to know where abouts the average toroid
> sits in relation to the curves in
>
> http://www.abelian.demon.co.uk/tssp/tmp/eddy-coupling.gif
>
> in other words, is a dryer-duct toroid more resistive than the
> 'worst case', ie somewhere between the green curve and the
> blue curve, or is it less resistive, ie between the green curve and
> the red curve? If the former, then reducing the resistance may make
> things worse. And how about a spun aluminium toroid - where does that
> sit? In view of the small Fres shift reported by those who have tried
> cutting the toroid, it may be nearer the blue than the red.
My guess is nearer the red. A cut terminal would be on a par loss-
wise with a good quality shorted turn wouldn't it?
> Plenty of room for useful experiments with this. Eg, take a toroid
> with a radial cut. Measure Q and Fres with a range of resistances
> bridging the cut. Should be able to form a graph showing the locus of
> the response peaks (imagine a U-shaped curve joining the peaks of the
> three curves in the image, touching the peaks of all the intermediate
> response curves. Question boils down to whether or not the resulting
> curve shows the whole U, or maybe just the left hand half, ie with
> zero bridging resistance the response doesn't go as far down as the
> green curve, and never gets up the other side because the toroid
> resistance itself is too high.
>
> It should be possible to demonstrate a U-shaped locus of the
> coupling by doing the above expt using the primary, with a
> variable resistance across the primary terminals (no gap, no cap), and
> CW feed into the base.
>
> Most interesting for me is the possibility of preventing the
> magnetic field from going into the ground - but that test will
> have to wait till the weather improves.
Well I ran my very first "proper" coil on a stainless steel benchtop
about 20 years ago. While its performance was not stunning (it
followed the wonderful recipe mentioned on the builder's list of a
single heavy turn in the primary and b-all turns in the secondary :)
it was a bit of a puzzle as to why it worked as well as it did until
I realized that the conductive benchtop was basically reflecting
energy rather than absorbing. the primary was positioned less than
three inches above the bench surface. And just for the record, its
relatively poor performance was unchanged when it was run on a wooden
desktop instead. The benchtop was earthed and used as an earth for
the coil.
Regards,
malcolm
> Cheers,
> --
> Paul Nicholson,
> Manchester, UK.
> --
>
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.