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Re: Evaluation needed Dan (fwd)
---------- Forwarded message ----------
Date: 13 Feb 1998 12:11:41 -0700
From: Dale Hall <Dale.Hall-at-trw-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Evaluation needed Dan
Dan and other Science Fair students,
What state are you in ? I am a county and state judge in CA. While we have never rejected a tesla project, we have imposed restriction such as not allowing power up demonstration (concern about electronic pacemaker upset though remote, is not worth the liability to the fair (it could put it out of business) or risk to those individuals). Suggest this to your teacher to at least allow you to enter, that you accept the challenge to present it without a power up exhibition. As I indicated to you in a private Email, use photos, charts, illustrations, demonstrated knowledge and graphs to convey the dynamics of your project. In many ways this is how you "sell" your wares to the world anyway and so it is great experience (HOW to sell your product without the dynamic in person demonstration transferring the burden of proving the project on your presentation skill). GL provided good review of your theory of operation, but much, much more is available on-line - do the research, but also note that there are subtlies that even the experts don't agree on. Perhaps you will be the one to unravel some of these secrets for which you need preparation and a creative, inquisitive and open mind that is based on solid basic Scientific Laws And Principles (SLAP - include these in you project presentation!). You are in the early stages of demonstrating that kind of skill !
Good luck and keep us informed -- dale.hall-at-trw-dot-com
------------------------------
Date: 2/13/98 0:50 AM
To: Hall, Dale
From: Tesla List
Date: Thu, 12 Feb 98 09:16:42 EST
From: Gary Lau 12-Feb-1998 0906 <lau-at-hdecad.ENET.dec-dot-com>
Subject: Re: Evaluation needed
>From: Dan Ressler [SMTP:danz_da_man-at-hotmail-dot-com] >Hey all,
>Im having trouble understanding the theory of the tesla coil and the
>tank circuit. But after much pondering I have come up with an
>explination that I think makes sense......so give me your input.
>
>A tesla coil is simply a special transformer that uses the series
>resonant circuit to step up the voltage of the input power. A series
>resonant circuit consists of a coil, a capacitor, and the resistance of
>the wire. Energy is stored on one terminal of the capacitor
Energy is stored in the dielectric layer of a capacitor, not on
either plate.
>and in the coil (the coil stores energy in a magnetic field, this is
>called inductance),
Energy in an inductor in is the form of a magnetic field but is
not called inductance, inductance is a property of the coil and
is the same regardless of whether any energy is stored in it or not.
>but as the capacitor fills up the magnetic field of the coil breaks down
>causing an inductive kick (theoretically this would result in a voltage
>in the coil infinitely high and infinitely short, but since the capacitor
>fills gradually the magnetic field is converted into electricity
>gradually). This energy then travels back through the circuit and builds
>up on the other terminal of the capacitor, and the process repeats its
>self until the energy is damped out by the resistance of the wire. This
>process is synonymous to a pendulum swinging back and forth. If energy
>is applied to the circuit at the right frequency (the circuit's resonant
>frequency) the voltage in the system will build up to huge voltages (in a
>perfect world the voltage would reach infinity). This is synonymous to
>pushing the pendulum at the right times so that its amplitude increases.
>In the case of the tesla coil the transformer adds energy into the tank
>circuit, not at the resonant frequency, but the voltage still escalates.
>When the voltage is high enough it jumps the spark gap. The gap produces
>"white noise", or all possible radio frequencies, one of these
>frequencies is the resonant frequency of the tank circuit.
You've got this all backwards. The first thing that happens is
the primary capacitor charges from the high voltage neon
transformer. There may be some 60 Hz resonant action here, but for
simplicity, let's say not, it's not pertinant to Tesla coil
operation.
As the voltage across the capacitor reaches the spark gap
breakdown voltage, the gap fires and conducts. It does NOT
produce white noise (at least not much). The conducting gap
places the charged capacitor in parallel with the primary coil,
and here is where the pendulum action takes place. The energy
alternately exists in the capacitor, then the primary coil. The
energy does not move from one side of the capacitor to the other,
although the polarity of the charge does alternate on alternate
"pendulum swings".
>The energy see-saws back and forth at the resonant frequency and the
>voltage jumps to extreme voltages.
Right, but the voltage rise occurs in the secondary, not the primary.
>Next, the secondary coil absorbs the
>energy in the tank circuit through coupling. When the energy in the
>primary circuit reaches zero the spark gap extinguishes, and the above
>process begins again. Meanwhile, the secondary coil is acting as a tank
>circuit by its self. The winding of the coil have a small capacitance.
>The coil also has inductance, energy is stored in a magnetic field, and
>there is resistance. These are all the components of a tank circuit.
>The tesla coil is designed so that the resonant frequencies of the
>primary coil and the secondary coil are the same; and the secondary
>absorbs the energy of the primary coil at this frequency. The result is
>the voltage climbs and climbs as it gets higher in the secondary coil.
>The voltage gets so high the electricity can flow through even air.
Pretty close. In addition to resonant rise, there is more to why
the secondary voltage gets so high. If the energy in the primary
capacitor (when the pendulum is on that side and the cap is fully
charged) is defined by E=.5*C*V*V, so must the energy in the
secondary capacitance when it is fully charged. Since the
secondary capacitance is a tiny fraction of the primary
capacitance, equating the primary and secondary energies shows
Vs = Vp sqrt(Cp/Cs). This is a gross oversimplification and
ignores all losses, but in principal is true.
Gary Lau Waltham, MA USA