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*To*: tesla-at-pupman-dot-com*Subject*: Re: [TSSP] Measured vs. Operating coil coupling?*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Tue, 15 May 2001 20:18:41 -0600*Resent-Date*: Tue, 15 May 2001 20:44:23 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <NdROE.A.ztG.BmeA7-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Terrell W. Fritz by way of Terry Fritz <twftesla-at-uswest-dot-net>" <terrellf-at-qwest-dot-net> Hi Paul, At 11:46 AM 5/15/2001 +0100, you wrote: >Terry, > >I agree with your comments to Ray, but I'll add a few of my own... > >4. With a large toroid, the top current can be a large proportion of >the base current, eg 70%, so that there can be a sizeable current >available for induction at the top. So we could see say 10 amps in the toroid. Interesting since we do not often think of the toroid as a current loop. However, perhaps we should!! > >5. The induced currents in a shorted turn, toroid, or ground sheet >are not in themselves a bad thing - in fact they can be quite useful >if carefully managed. Its the I^2R loss in the shorted loop that >really counts, and whether or not the shorted loop destroys the Q of >the coil depends on the impedance match between the loop resistance >and the rest of the system. For any shorted loop there will be a >worst possible loop resistance that will have, for the particular k >factor involved, the max impact on system Q, and that worst resistance >will be the matched resistance. If the loop R is below or above this, >the impact on Q will be reduced accordingly. Thus a shorted loop which >has a very low R will only have a tiny effect on Q, even though the >induced current can be quite high, as seen by the apparent reduction >of the secondary inductance. To demonstrate this qualitatively I've >generated a set of response curves for a resonating solenoid coupled >to a shorted turn: > > http://www.abelian.demon.co.uk/tssp/tmp/eddy-coupling.gif > >The green curve is the worst-case scenario - the resonator is well >matched to the shorted loop resistance of 1K ohms and the Q is very >low. The blue and red traces show the response with a loop resistance >of 100K ohms and 10 ohms respectively, and you can see that, when we >are well away from the 'matched' resistance, the effect of the >shorted turn on the Q is much reduced. > >So the moral is - if you're going to have a shorted turn, make it a >good one, eg the nice wide conductor of the toroid. There is an >advantage to this ... What a fascinating set of curves! It is not a big deal to add an outer aluminium tape ring to a toroid made from dryer duct to vastly decrease the resistance of the loop. Dryer duct toroid tend to have strangely poorer performance than smooth toroid. Perhaps this is a truly new concern for toroid builders! I also note that 5% frequency shift!! E-Tesla does not consider such things affecting resonant frequencies... I feel some experiments coming on :-)) snip... > >Yes, I've prepared two graphs showing the V/I profiles of Marco's >Thor system when driven by a CW voltage applied to the (untuned) >primary terminals, as modeled by tssp: > > http://www.abelian.demon.co.uk/tssp/tmp/tviplot.thor-p.60.gif > http://www.abelian.demon.co.uk/tssp/tmp/tviplot.thor-p.66030.gif > >for drive at 60Hz and at 66.03kHz respectively. Clearly we can expect >the k factor at the operating frequency to differ from that measured >with low frequency currents, although of course the mutual inductance >is the same in both cases since that is frequency-independent and is >fixed by the geometry of the coils. > >As you know, tssp's time domain simulator is currently under test, so >hopefully over the next few months we can turn up some reliable >statements about how the effective operating k relates to the mutual >inductance M. Note that the familiar formula k=M/sqrt(LpLs) only >applies to coupled resonant circuits where the two separate coils are >tuned to the same frequency, and when the system is driven near to >that frequency. Away from resonance, or with mis-matched resonators, >the k is a more complicated expression, so we are on shaky ground if >we try to talk about k at 60Hz - better to stick with M. > >On the whole, I'd expect a modest Fres shift - say of order 1% down, >on making a radial cut through the toroid, but no noticeable >difference in performance. I believe this has been reported by those >who have taken the trouble to test this. E-Tesla tends to have a little unaccounted for error in the sub 1% area. Perhaps this is the key! > >Just to add one final piece of speculation, there is some possibility >that the shorted turn of the toroid may be of some slight benefit, in >that it's resistance may dampen the higher resonant modes rather more >than the two desired operational modes either side of Fres, thus >perhaps usefully suppressing the unpleasant consequences of higher >mode excitation, eg racing arcs and difficult quenching. Plenty of >research to be done on this topic. Yep!!!! > >By all means forward these comments to the pupman list if you wish. I did! > >Cheers, >-- >Paul Nicholson, >Manchester, UK. >--

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