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*To*: tesla-at-pupman-dot-com*Subject*: Re: Toroid Eddy Current?*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Tue, 15 May 2001 07:23:54 -0600*Resent-Date*: Tue, 15 May 2001 07:43:01 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <-NdAUD.A.4gD.FJTA7-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz> Hi Terry, I think of your three possibilities below, the current distribution is possibly the one that counts most unless the terminal is plonked right on the top of the windings. I can't buy the conductivity argument - toroids can and are made to be very conductive. It's an interesting one though - the presence of the terminal does modify the current distribution. As far as coupling goes - consider the difference between a flat spiral positioned a couple of inches below the bottom resonator turn (which can easily give k of 0.2 to the resonator) and a flat-bottomed "toroid" of the type I use positioned a couple of inches above the top of the coil. ?? Malcolm On 14 May 01, at 21:49, Tesla list wrote: > Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net> > > 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-dot-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-dot-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 > > > > >

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