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*To*: tesla-at-pupman-dot-com*Subject*: Coil Efficiency (was megavolt)*From*: "Greg Leyh" <lod-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)*Date*: Sat, 09 Sep 2000 12:43:37 -0600*Delivered-To*: fixup-tesla-at-pupman-dot-com-at-fixme

Original poster: Terry Fritz <twftesla-at-uswest-dot-net> >> >> [1/2 * Cp * Vp^2] * 75% = 1/2 * Cs * Vs^2 >> > > This equation could be re written to: > > Vs = Vp x SQRT(Cp/Cs) x SQRT(0.75) > > Which can be equivalent to: > > Vs = Vp x SQRT(Ls/Lp) x SQRT(0.75) > > Which is: > > Vs = 0.866 x SQRT (Ls/Lp) > > "i" usually estimate the secondary voltage as: > > Vs = 0.5 x SQRT (Ls/Lp) > > For most small coils, I am fairly confident that "the factor" is 0.5 to 0.6 > > If your are fairly confident that the factor is "around" 0.87 for your > "really big" coils, (that the rest of us can only dream of ;-)) it would > provide an interesting comparison of the efficiencies of large coils vs. > smaller coils... I am not confident of the exact efficiency values by any means, but I would expect a TC to be easily above 70% efficient. A 'factor' of 0.87 implies an efficiency of 75% (0.87 * 0.87) A 'factor' of 0.60 implies an efficiency of 36% (0.60 * 0.60) A 'factor' of 0.50 implies an efficiency of 25% (0.50 * 0.50) My rotary drops about 1300V at 2800A. Since the primary is a 26kVDC system, the rotary loss is about 1300/26000 or about 5%. There are no other obviously dissipative components (warm to the touch, at least) in the coil system. So I can't imagine how more than 20% of the coil's throughput could be dissipated as heat. I'm sure that the stationary electrodes would glow red, if they were radiating any more than a kilowatt or two. The throughput with the new primary configuration is only 28kVA. Empirical evidence seems to hint that the smaller coils are more efficient than larger ones. I suspect that this has to do with the squared/cubed scaling laws -- A coil that's twice as big has to fill *eight* times the volume with magnetic flux.. -- -GL www.lod-dot-org

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