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Re: Tesla Coil Q Factors
Date forwarded: Tue, 25 Aug 1998 23:36:08 -0600
Date sent: Tue, 25 Aug 1998 23:08:50 -0600
To: tesla-at-pupman-dot-com
Subject: Re: Tesla Coil Q Factors
Forwarded by: tesla-at-pupman-dot-com
From: Tesla List <tesla-at-pupman-dot-com>
From: bertpool-at-ticnet-dot-com
> 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. 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.
> Compute this value for a number of sample shots for the correct log
> decrement value and divide into pi to obtain the actual dynamic operating Q
> factor. The value is usually accurate to within 1% for most systems. Once
> this Q factor is determined the peak currents can be easily calculated and
> other interesting data drops out as well including max peak system
> potential, system characteristic impedance, etc. The derivation of this
> equation is via simple substitution with the energy conservation equation,
> ie, 1/2cv^2. Morecroft and Termain both discuss this Q decrement factor
> equation but John is the first among modern theorists to discuss its
> application.
>
> 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
>
> ----------
> > 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 --
> >
>
>
I would like to second DC Cox's support of John's program and manuals. I
have
found both to be of great value, and that value comes from John using
real-world
coils as the foundation for his program's calculations. I too have sent John
detail info on several different coils as a base-line. Maybe one day we'll
have
enough experience in magnifier construction to begin the process of designing
a decent maggie program!
Bert Pool