From: "Malcolm Watts"
Date: Tue, 15 May 2001 17:54:29 +1200
Subject: Re: [TSSP] Measured vs. Operating coil coupling?
Hi Terry,
On 14 May 01, at 22:20, Terrell W. Fritz wrote:
> Hi All,
>
> I am wondering if the measured (at say 60Hz AC) primary to secondary
> coupling is the same as the coupling an operating coil sees? What
> makes me wonder if they are different is the current profile along the
> secondary at 60Hz AC may be different than the operating profile such
> as example 8 at:
>
> http://www.abelian.demon.co.uk/tssp/pn1710/
>
> Perhaps the 60Hz AC and operating secondary current profiles are very
> close. However, if there is any difference, it seems like the
> coupling would also be affected buy the different secondary current
> profiles in the two cases. Perhaps there is a resonant or dynamic
> coupling coefficient that is different from the low frequency steady
> state coupling? I imagine they would not be too different at any
> rate, but the effect may be real...
According to my measurements there is little difference. That's not
to say that there isn't a measureable difference - just that if there
is it appears to be small. I normally measure k off the beat envelope
or by doing the spectral sweep in the coupled system with a high Z
source across the tank circuit.
> The effect of the top toroid as a shorted turn came up on the Tesla
> list and I copied it below for reference...
That topic has cropped up a few times in the past. I note that you
stated the simulation assumed that the terminal was 10" above the
windings. The k you found was entirely reasonable for that degree of
separation but is much too low for many coils whose terminals are
mounted just a couple of inches above the windings. It should
definitely be subject ot modelling in my opinion. Also, the modelling
should investigate the profiles when it is a shorted turn and when it
is slitted. Curious that the frequency differences are not greater in
practice than one would think. Something else for Paul to choke over.
Regards,
malcolm
> Cheers,
>
> Terry
>
>
> >From: "Terry Fritz"
> >To: tesla@pupman.com
> >Subject: Re: Toroid Eddy Current?
>
> >Hi Ray,
> >
> >I think there are three factors at work that diminish the shorted
> >turn effect for toroids.
> >
> >1. The coupling is not real high. I used MandKV31 (coupling
> >calculation program*) to find the coupling for a 22 inch C-C toroid
> >with an 8 inch cord that was 10 inches above a 30 inch long 10.25
> >Dia. secondary with 1000 turns. The coupling was only 0.028.
> >
> >*
> >http://hot-streamer.com/TeslaCoils/Programs/Programs.htm
> >
> >2. Toroids are not real good conductors. Corregated dryer pipe and
> >other aluminum materials are faily resistive to RF currents. Not
> >sure how much difference that makes but...
> >
> >3. There is not much current near the top of the coil. As Paul's
> >TSSP project and my tests have shown.** Thus, there is not a lot of
> >nearby current to couple to the toroid.
> >
> >**
> >http://hot-streamer.com/TeslaCoils/MyPapers/NSVPI/NVSPI.htm
> >http://www.abelian.demon.co.uk/tssp/pn1710/
> >
> >I think all three of these have some affect and add up to only a
> >small Eddy current effect from the toroid. The actual numbers and
> >all are a bit fuzzy but it could probably all be figured out with a
> >fair amount of precision.
> >
> >Cheers,
> >
> > Terry
> >
> >
> >At 09:58 PM 5/13/2001 -0700, you wrote:
> >>Doesn't the toroid form a single shorted turn that would dampen the
> >>secondary by lowering the Q? It seems that the toroid is close
> >>enough to the secondary to have an effect. An interesting test could
> >>be performed if someone had a working coil with an identical spare
> >>toroid. That spare toroid could be cut with a band saw radially
> >>toward the center stopping couple of inches from the middle.
> >>Probably 3 or 4 (maybe more) equally spaced cuts would be adequate
> >>and maybe dabs of epoxy to stabilize the cuts. Then install the
> >>modified toroid, retune the coil and compare the results with the
> >>original toroid.
> >>
> >>Maybe I'm off base but I have never seen this discussed and if the Q
> >>of the material for the secondary coil form matters, seems this just
> >>might.
> >>
> >>Ray
> >>
>
>
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.