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*To*: tesla-at-pupman-dot-com*Subject*: Re: E-Tesla = Medhurst*From*: Terry Fritz <twftesla-at-uswest-dot-net>*Date*: Sun, 11 Jun 2000 23:04:48 -0600*Approved*: twftesla-at-uswest-dot-net*Cc*: alwynj48-at-earthlink-dot-net, malcolm.watts-at-wnp.ac.nz*Delivered-To*: fixup-tesla-at-pupman-dot-com-at-fixme*In-Reply-To*: <001301bfd3cc$2aaaf7e0$03000004-at-oemcomputer>

Hi Bob, At 01:40 PM 6/11/00 -0400, you wrote: >Hi Terry. > >After a little more thought or was it a lot more thought. > >For a large parallel C the voltage a long the coil approaches a linear >function regardless of what the distribution is with out parallel C. ie the >current flowing in the distibuted intrinsic C hardly effects the voltage >across the coil because the coil current is much higher than the intrinsic C >current. > >Hence the additional current flowing in to the distributed intrinsic C is >only a function of the voltage and C. This is even true for low H/D (<0.25) >with almost unity coupling (auto transformer action). > >Under such condition the distibuted intrinsic C can be refereed to one end >by simple summing the currents. Because the currents are proportional to >the voltage a voltage weighted intrinsic C is equal to a single C you must >put in parallel with the coil to have the same total current flow that the >distibuted intrinsic C had. > >Hence if you run E-Tesla with a linear voltage and on an isolated coil it >will produce med C. This is a theoretically valid comparison and should >correlate to approximately. 1% in C not F. A good test of the theory and >model. Ok. I stripped out E-Tesla5.50 to put a linear voltage on the secondary and stick it in free space and all that. The program is at: http://users.better-dot-org/tfritz/site/programs/ETMED.ZIP I then ran the program with a 200 grid on 10 inch diameter coil of various lengths. I then compared the results to Medhurst. H/D Cmed C ET5 calc Error % 10.0 1.32 1.2056 -8.66 9.0 1.22 1.1238 -7.89 8.0 1.12 1.0482 -6.41 7.0 1.01 0.96745 -4.21 6.0 0.92 0.88716 -3.57 5.0 0.81 0.80313 -0.85 4.5 0.77 0.75848 -1.50 4.0 0.72 0.71428 -0.79 3.5 0.67 0.66897 -0.15 3.0 0.61 0.62244 2.04 2.5 0.56 0.57424 2.54 2.0 0.5 0.52573 5.15 1.5 0.47 0.4758 1.23 1.0 0.46 0.42783 -6.99 The graph is at: http://users.better-dot-org/tfritz/MedComp.gif Note that both graphs have a bend at 5.0!?! Must be something magical happening at that point. Below 5.0 Medhurst tracks very well until the coils get really small. I wonder if the error is him or us? :-) ET5 looks like two straight lines while the Medhurst graph is showing obvious signs of a little experimental error. The program did about 300 billion more calculations than Medhurst did so it should be straight! :-)) I wonder if I dare say that the computed numbers "may" be more accurate than Medhurst's in the 2.5 to 5.0 range? Looks like Bob is again right!! > >If you run it with a ground plain it will produce med C with a ground plain. >But as Medhurst did not produce such a table you can not make any valid >comparison. The true C / TM equation is again theoretically valid for an >isolated coil. > >When I say valid for..... I dont mean its not valid for other conditions it >means only that I can only prove its valid for that condition/s. > >So E-Tesla can be said to be theoretically accurate for coils with >approximately 1000 turns (low turn to turn C effects), for large top loads >and with a ground plain sufficiently below the coil (at least several >diameters) that the inductance is valid. > >Note E-Tesla must include some internal C (turn to turn C) effects because >the C is determined with a voltage profile as opposed to a unity profile >(the correct way to calculate intrinsic C) then weighting the result with >the voltage profile. However as the internal C has mostly internal >current I don't know if it can be refereed to the one end and I don't if how >you treat the internal coupled flux is valid or correctly produces a >reffered C to one end. That will require more thought but as I believe its >a small effect I am not motivated to try. If you try it both ways and the >answer (refereed C or med C) is significantly different then I will be >motivated to try. > >Now what about the self resonant case. When the only current flowing in the >coil is due to the distributed intrinsic C both the voltage and current are >not linear so the above method of referring the intrinsic C to one end is >not valid. A 5% to 10% error in F is 10% to 20% error in C or L. I am working on such things to further increase accuracy... Cheers, Terry > >Regards Bob > >You can put this on the list if you think anybody else is interested >

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