Re: TESLA COIL REVISED

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


At 3.5 MHZ your radiation losses would be significant.

Dr. Resonance

Resonance Research Corporation
E11870 Shadylane Rd.
Baraboo   WI   53913

 >
 > > >I said no such thing.  A 50-turn secondary would result in a very high
 > > >resonant frequency.  Since AC resistance increases with frequency, such
 > > >a coil would have a higher resistance than one operating at a lower
 > > >frequency.  The lower Q would probably result in inferior performance.
 >
 > >NOT SO. Let's compare a 1000-turn 3" diam. thin wire secondary with a
 > >50-turn 12" diam. thick wire secondary. The 1000-turn coil has
 > >inductance of about 9 mH, and the 50-turn one has 255 uh inductance.
 > >And since that makes the inductance of the 50-turn coil, 35 times
 > >LOWER, it will have THE SAME reactance at 3.5 MHz, as the 1000-turn
 > >coil has at 100kHz.
 >
 > This assumption is entirely disregarding the effect of increasing
frequency
 > on real world losses in the secondary system.
 >
 > >So you can see that the reactance of the 1000-turn coil is about 5600
 > >ohms at 100kHz, and the reactance of the 50-turn coil is ALSO 5600 ohms
 > >at its resonant frequency of 3.5 MHz.
 >
 > It is indeed very true that the reactive impedance due to secondary
 > inductance is the same in the two systems that you have described, but
this
 > system also has a self capacitance to be contended with, as well as
 > resistive components of the impedance.  Skin effect losses greatly
increase
 > the effective resistance of a given material at increasing
 > frequencies.  See Gary's inquiry into the question of primary losses on
his
 > web site.  While the currents are much lower in the secondary system, they
 > are still present, and since the secondary wire length is comparatively
 > long, even in a 50 turn design such as you have proposed, the secondary
 > resistive losses will have to be considered.  I don't have the time right
 > now to run the numbers assuming a copper conductor in the two cases
 > discussed here, but be assured that the AC resistance of any material at
 > 3.5 MHz is far from negligible.
 >
 > >So what you said is a MYTH. The 50-turn coil resonates at higher
 > >frequency, but it WOULD NOT have a higher resistance than one operating
at
 > >a lower frequency.
 > >
 > >Now, since the output voltage of CLASSIC TC depends on the L2/L1 ratio
 > >instead of a resonant rise, this design wouldn't be good for classic TC
 > >because the output voltage would be rather low. BUT, it WOULD be
 > >perfect for a SOLID-STATE Tesla coil, because this coil produces
 > >RESONANT RISE (as you yourself mentioned).
 >
 > I also need to interject here too.  A resonant frequency of 3.5 MHz is
 > hardy a frequency that most solid state tesla coil builders can consider
in
 > their design.  To date I am only aware of one person, Dan McCauley, who
has
 > successfully built a solid state coil with an Fres in the megahertz range
 > with any substantial (>100 W) input power without almost instantly
 > destroying the power circuitry.  Most of us don't have the skillz (yes,
 > with a z) necessary to pull this feat off.  Now this operating frequency
is
 > not out of the question with tube coils, but dealing with power supply
 > design becomes much more difficult as frequency increases when any stray
 > loop or conductive object close to the circuit causes changes in
operation.
 >
 > >So now that we know that a 50-turn secondary doesn't have higher losses
 > >than a 1000-turn one, even though it resonates at much higher frequency
 > >(several MHz), we can see that the 50-turn secondary is a superior
 > >design when used in SOLID-STATE Tesla Coils.
 >
 > Superior only in one regard - higher *apparent* Q on paper neglecting real
 > world performance differences due to skin effect and other resistive
losses.
 >
 > >And that's because while the output voltage of 1000-turn coils is
 > >limited by the L2/L1 ratio, the 50-turn solid-state TC has no such
 > >limitations, and will build up the output voltage to ANY LEVEL that the
 > >insulation will allow.
 >
 > While theoretical discussions are good, especially for increasing one's
 > understanding of a subject and consequently one's ability to construct a
 > working Tesla coil, diagnose problems, and effectively eliminate/reduce
 > those negative effects, it is not helpful to completely ignore obvious
 > limitations, i.e. funding, practicality, safety, human error, etc.
 >
 > >Of course the higher frequency will result in shorter sparks, so this
 > >coil would be more for people who want to experiment with very high
 > >frequencies and perhaps experience beams or walls of light (brush-like
 > >discharge), instead of the sparks. And that brush-like discharge would
 > >probably be more plasma-like than the usual low-frequency sparks.
 >
 > Erm, if the definition of plasma is a fourth state of matter more
energetic
 > than the gasseous state in which electrons have been stripped off of their
 > respective atoms creating a conductive, almost certainly luminescent
fluid,
 > then "the usual low-frequency sparks" look a whole lot like plasma to me
;)
 >
 > >Jaro
 > >
 > > >
 > > >Regards, Gary Lau
 > > >MA, USA
 > > ><snip>
 >
 > Regards,
 >
 > Chris Arnold
 >
 >
 >
 >