Re: Q Factor and Overall Efficiency

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

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.
 
> 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.
 
> 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
  
> 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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> 
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