From: "Terrell W. Fritz"
Date: Wed, 30 Aug 2000 12:49:28 -0600
Subject: Re: [TSSP] Q mesurements
Hi Paul, I once (2 years ago) measured the Q of this secondary but with a bit larger toroid for modeling purposes. Q bare = 63.5 Q terminal = 78 So with about two years in between I get roughly the same numbers. That was done with the secondary on the coil in a none perfect environment but still fairly close for comparisons. I used this to come up with my lumped element model for this coil. Please refer to: http://63.225.104.218/test/TeslaCoils/Misc/PaulNich/LumpedSecModel.gif In this secondary model, the 75.4mH coil (L1) is seen with the effective 391 ohm AC resistance Rsec (I think I did an AC resistance measurement to find that). The self capacitance (Cself) is just the Medhurst type but this is an actual measured value. Ct is the added terminal capacitance. What is of interest here is that I added the two resistances Rcself and Rct to account for the Qs of the bare and terminated cases. The self capacitance seemed to have its own loss as did the terminal capacitance. I figured that the terminal had a lower AC resistance do to its greater size and larger current path the ground. I assumed the current "loop" in this circuit was not a perfect conductor and the added resistors accounted for the currents traveling through various objects like the ground, wall, floor, etc. In other words, Cself and Rct or far from loss less capacitors. Thus, the terminated case did indeed have a higher Q. I just made all this up at the time, but perhaps the idea is of use to us now... I can't think of anything that would raise the Q 2X as you suggest. All my setup and techniques should be sound (at least on the third try ;-)) but I am open to any ideas... I would think such a thing makes sense and it could be easily added to the computer model's discrete transmission line calculations. Of course, "finding" the values of the resistances in the new model is left to the reader ;-)) Richard Hull once told me trying to figure out Tesla coil secondary theory will "simply drive you nuts!!" Welcome to the club ;-))) Cheers, Terry At 11:33 AM 8/30/00 +0100, you wrote: >Another set of Q measurements from Terry. > >Terrell W. Fritz wrote: > >> OK, I redid the Q measurements with a <0.5 ohm signal >> generator and measured peak voltage instead of RMS. >> So I "think" I did it right this time ;-) > >Yup, I dont think it matters RMS or peak so long as you >keep to one or the other. > >> I put the signal generator and a tiny antenna near to >> the base of the coil out of necessity but they should >> not have had any great effect. > >OK, we expect it to pull the frequencies around a little, >no problem so long as its all stable during the run. > >These are still for the familiar Big LTR coil. > >> 45 inch Torroid coil: >> Fl2 = 97.28 kHz >> Fo = 97.84 kHz >> Fh2 = 98.45 kHz >> Q = 83.62 >> >> Bare coil: >> Fl2 = 147.1 kHz >> Fo = 148.4 kHz >> Fh2 = 149.7 kHz >> Q = 57.08 > >Qualitatively different now, the toroided coil now has the >best Q, so somethings changed. Q factors are more realistic >now. Ultimately I think we should be seeing 150 to 200 at >least. > >> I then took my trusty knife and slashed my foil ground plane >> right down the center with only the center connecting both >> halves... > >...expecting a significant improvement, now that the longest >and therefore the heaviest coupled current loops are broken... > >> 45 inch Torroid coil: >> Fl2 = 96.55 kHz >> Fo = 97.2 kHz >> Fh2 = 97.92 kHz >> Q = 70.95 >> >> Bare coil: >> Fl2 = 145.5 kHz >> Fo = 147.1 kHz >> Fh2 = 148.5 kHz >> Q = 49.03 > >Aargh! Both Q factors have gone down in the same ratio, when >they should have gone up! Frequencies have not altered much so >the basic geometry was unchanged by the cut - good, but they've >gone down slightly rather than up - puzzling. > >> I remeasured the secondary's inductance at 75.1mH. > >Good, the inductance has increased slightly from the >original measured 74.1mH, which is consistent with >splitting the ground plane, but the frequencies have gone >down! > >> Looks like the measurements are going a little opposite to >> what is predicted. I assume that just makes it more >> interesting and fun :-)) > >Gosh, you're right about that! Usually means we're about to >learn something. This'll certainly take some explaining, right >now I'm at a loss (excuse pun!). > >Cheers, >-- >Paul Nicholson, >Manchester, UK. >--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.