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*To*: tesla-at-pupman-dot-com*Subject*: RE: Q Factor and Overall Efficiency*From*: "John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)*Date*: Sat, 02 Sep 2000 13:49:17 -0600*Delivered-To*: fixup-tesla-at-pupman-dot-com-at-fixme

Malcolm - It looks like we are back to square one as in the past posts. So maybe when more coilers are interested we can review this again. John Couture ------------------------------ -----Original Message----- From: Tesla list [mailto:tesla-at-pupman-dot-com] Sent: Tuesday, August 29, 2000 8:07 PM To: tesla-at-pupman-dot-com Subject: RE: Q Factor and Overall Efficiency Original poster: "Malcolm Watts" <M.J.Watts-at-massey.ac.nz> On 29 Aug 00, at 18:41, Tesla list wrote: > Original poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net> > > > > -----Original Message----- > From: Tesla list [mailto:tesla-at-pupman-dot-com] > Sent: Monday, August 28, 2000 7:32 PM > To: tesla-at-pupman-dot-com > Subject: Re: Q Factor and Overall Efficiency > > > Original poster: "Malcolm Watts" <M.J.Watts-at-massey.ac.nz> > > hi John, > > On 28 Aug 00, at 0:50, Tesla list wrote: > > > Original poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net> > > > > > > The Q factor tests have been discussed many times in past List posts. > > However, these tests give the Q factor in a low voltage condition. This is > > not the TC operating Q factor. The operating Q factor would give the > > secondary voltage with the equation > > Vs = Vp * Q > > where Vp is the primary peak voltage. > > I don't agree that this is valid for a disruptive TC and I > have stated why many many times so I won't repeat myself yet > again. Operating unloaded Q can easily be found by measuring > the decrementing waveform on an oscilloscope. I have found it > is pretty much the same as the results I've obtained in low > level tests. > ---------------------------- > It is a well known fact that increasing the primary voltage (Vp) will > increase the secondary voltage (Vs) of a disruptive TC with no other > changes. This means the Q factor would also increase. Does this mean there > is a flaw in what you stated in the past? Are you speaking of secondary unloaded Q or system Q? Qs hardly changes. Qp (which is really undefined due to its voltage/current dependency) also goes up if Vp is increased but it is a time-arying quantity. But why is a change in any Q necessity at all? Suppose Q in your equation is constant. Then Vp is proportional to Vs. I can't see any flaw in what I've stated in the last few years with regard to this subject. > You indicated that you found the operating Q and the low level Q to be > pretty much the same. In your "Effective Resistance" post you said you did > not believe your coil with an unloaded Q of 300 (low level) would generate > 2.7 MV (operating). This would mean you did not believe the low level Q was > not pretty much the same as the operating Q. Am I reading this conflict > correctly? No, definitely not. See above comments regarding the constancy of Q. Also note that in a disruptive coil that relationship (Vs = Q.Vp) *cannot* apply. Why? Let Q = infinity. Then the implication is that Vs is infinite regardless of primary voltage. But primary voltage *is not constant*. It is decrementing from the moment the gap fires. You are feeding a limited quantity of energy in and that shot of energy *has to* charge the secondary capacitances. Even in a lossless coil (i.e. Q = infinity), that limitation remains. Malcolm > ----------------------------- JHC > > > To find the operating Q factor would require only a scope and the proper > > probe and the knowhow. To do the test find the half power points while the > > Tesla coil is operating. Then determine the Q factor with the equation > > Q = Fr/(Fh - Fl) > > I think there is some misunderstanding here. You can find Fh > and Fl in low power tests by sweeping a signal generator > feeding the coil above and below Fr but how do you get a > frequency sweep on a coil that is ringing all by itself? The > only resonable way to measure Q when there is a single > frequency present is to calculate Q off the decrementing > waveform (as you've already stated). Both methods are > equivalent and the second can also be done at low power if the > secondary is shock excited. > ---------------------------- > You are 100% correct in that the operating Q cannot be found by sweeping the > frequency of a coil that is ringing all by itself. The equation Q = > Fr/(Fh-Fl) cannot be used in this test. As you state the Q would have to be > found by the decrementing waveform (as I show in my TC Notebook). The > equation Q = Pi/Log Dec would have to be used. So now I have stuck my > foot in my mouth. > > -----------------------------JHC > > > where Fr is the resonant frequency, Fh is the higher half power frequency, > > and Fl is the lower half power frequency. The Q factor would be the > voltage > > gain from the TC input to the TC output. This gain could then be used to > > find the overall efficiency of the TC system. This would be done using the > > energy equation > > Vs = sqrt(2J/Cs) > > Overall efficiency would be the Vs(half power) test volts divided by the > > Vs(energy) theory volts. > > Am I correct in thinking you want to compare Vs (=sqrt(2J/Cs) > with Vs = Q.Vin? You are comparing apples and oranges sorry. > > Malcolm > ------------------------- > Overall efficiency is = energy out/energy in. However, because energy out > with a disruptive TC cannot be determined an overall TC efficiency can be > roughly estimated with the equation > Vs = Vs test/Vs theory where Vs test = Vs = Q Vin and > Vs = sqrt(2J/Cs). > Another method to estimate the overall efficiency of a TC is shown in my > Tesla Coil Construction Guide. Coilers often mention TC efficiency but do > not indicate how they determined this ellusive parameter. > ---------------------------------- JHC > > > This operating Q factor and TC overall efficiency may be a first in the > > design and engineering of Tesla coils. However, Terry Fritz may have > already > > done this? Have other coilers done this? > > > > John Couture > > > > --------------------------- > > >

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