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Re: Tesla Coil Q Factors
X-Envelope-From: DR.RESONANCE-at-next-wave-dot-net Wed Aug 26 14:06:03 1998
to: Bert
Wattage vs. Q is an interesting challenge. I think it could be derived as
follows: first, realizing that wattage, ie, power, is potential times
current. Now current depends on load impedance, ie, a certain amount of
resistance will "draw" or allow on a certain amount of current flow. Q
also uses resistance in its equation so it is indirectly related to power
or wattage thru its common tie of circuit resistance and impedance. I
think a mathematical derivation is quite possible to tie wattage levels
directly to dynamic operating Q factor assuming other good design factors
are being followed (perhaps a good job for Mark R. --or John). Have fun.
DR.RESONANCE-at-next-wave-dot-net
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Tesla Coil Q Factors
> Date: Wednesday, August 26, 1998 7:42 AM
>
> Tesla List wrote:
> >
> > to Bert
> >
> > John's second equation is the foundation for all of Tesla's magnifiers:
> > The output potential of an RF inductor is equal to the applied
potential x
> > its dynamic operating Q factor.
>
> OK... but the original discussion refered to 2-coil systems, and the
> seeming disparity between the predicted and actual behavior of Q as
> input wattage was increased. John's materials do not cover magnifiers.
>
> The third equation is perhaps the most
> > interesting of all. It allows all coilers to easily find their dynamic
> > operating Q factor of any system (classic or magnifier) by simply using
a
> > storage scope or shooting some camera pictures of a regular scope's
display
> > and then finding the decrement factor, ie, log amplitude 1/ amplitude
2.
> <SNIP>
>
> I agree. This, and other similar approaches, are very valuable for
> measuring dynamic Q on a "sparking" system.
>
> >
> > I've also noticed on this List that ocassionally some "builders" like
to
> > "pick on" John as a theorist --- much like experimental physicists
> > jealously like to "pick on" theorists in their field. Many years ago I
> > provided John with the hard data on dozens of our commercial coils --
data
> > that he has carefully and thoughtfully distilled to produce his
manuals.
> > His manuals and books are correct from both a practical and
theorectical
> > standpoint and will withstand scrutiny from any builders standards.
John's
> > books and manuals provide excellent guidelines for all coil builders
and
> > are especially invaluable to the new coil builders on the Tesla List.
It is
> > unfair and most of all blatantly incorrect to assume John is an ivory
tower
> > builder. His data is correct and not all derived for theorectical
> > constructions. Enough said on this subject (ps Bert -- I wasn't
implicating
> > you in any manner). Your insights are always a welcome treasure to the
> > List.
> >
> > DR.RESONANCE-at-next-wave-dot-net
>
> No problem! I also have provided John with measurement data on various
> occasions, including instrument and dynamic Q using an approach that was
> similar in principle to log-decrement. My concerns were more from the
> theoretical side to address what was probably a typo in the first
> equation, and to better understand the applicability of Q = Vs/Vp in the
> classical 2-coil case. It's not yet clear to me how this relationship
> holds for the classical 2-coil case.
>
> After exploring the derivation with John, we may find that the apparent
> disparity in Q vs wattage to which John refers stems from one or two
> assumptions that are being violated in the 2-coil case. It's still not
> clear that a direct relationship should exist between wattage level, Vs,
> and Q, although there may be a degree of correlation for other reasons.
>
> -- Bert --
>
> >
> > ----------
> > > From: Tesla List <tesla-at-pupman-dot-com>
> > > To: tesla-at-pupman-dot-com
> > > Subject: Re: Tesla Coil Q Factors
> > > Date: Tuesday, August 25, 1998 5:26 PM
> > >
> > > Tesla List wrote:
> > > >
> > > > ----------
> > > > From: John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> > > > Sent: Monday, August 24, 1998 11:57 AM
> > > > To: Tesla List
> > > > Subject: Tesla Coil Q Factors
> > > >
> > > > To All -
> > > >
> > > <SNIP>
> > >
> > > Q = 6.283 x F x L Q = Vs/Vp Q = 3.1416/ Log Dec
> > >
> > > <SNIP>
> > > > With real coils the secondary voltage Vs increases when the input
> > wattage
> > > > is increased. This means that in the equation Q = Vs/Vp the Q
Factor
> > would
> > > > increase with an increase in wattage. However, with real coils just
the
> > > > opposite happens. The Q Factor decreases as the wattage increases.
I
> > show a
> > > > graph in one of my books of this relationship where the Q Factor
> > decreases
> > > > with an increase in the wattage. To my knowledge there is nothing
in
> > the
> > > > present literature that shows why there is this apparent
discrepancy
> > with
> > > > the equations.
> > > >
> > > <SNIP>
> > >
> > > John,
> > >
> > > The first equation is not quite right - it should be:
> > > Q = (6.283 * F * L)/Reff
> > > where Reff is the combination of AC resistance in the circuit due to
> > > resistance, skin effect, winding proximity effects. As you indicate,
> > > determining the Q's of the primary and secondary circuits in a
sparking
> > > coil is tougher, but can be estimated by looking at waveforms and
> > > back-calculating.
> > >
> > > However, output voltage is not directly relatable to input wattage,
> > > although you will see a degree of correlation: larger systems tend to
> > > use larger tank caps and higher primary voltages, and need more power
to
> > > achieve similar breakrates. Output voltage is more directly a
function
> > > of bangsize and system losses, since disruptive coils do not build-up
> > > secondary energy from bang to bang. Sparklength is another matter...
> > >
> > > I'm not familiar with Q = Vs/Vp - how was this equation derived?
> > >
> > > -- Bert --
> > >
>