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Re: Now, How does a coil really work??
At 03:10 AM 1/21/99 -0700, you wrote:
>Original Poster: RWB355-at-aol-dot-com
>
>Hello all,
>
>
>After reading some of the comments on my post about a TC coil not
experiencing
>resonant rise (spark length increase is due to the resonant rise), I have
>become more confused than ever.
Not suprizing
>I will believe that the primary circuit experiences LC resonance (that is
what
>we want, if I understand it correctly) and that this will increase the amount
>of energy available in the primary in comparison to a single shot from the
cap
>to the primary coil w/o resonance (i.e: a simple discharge of a charged cap
>into a certain coil with little or no LC resonance occuring).
Look at it this way:
You know a capacitor can be slowly charged, or filled with DC current. Think
of the LC tank as an AC capacitor. Each pulse of energy delivered in phase
to the tank, like periodicaly giving a swing a push, will be stored by it
until losses equal the rate energy is delivered to it. This is what resonant
rise is.
>I will also believe that in order to transfer as much energy as possible you
>will want the secondary to resonate at the same FRes as the primary.
You must deliver the pulses at the appropriate time, or phase the energy,
true. But since if the system is overcoupled energy bounce back into the
primary, thats not necessarily true. An overcoupled pri/sec off-tuned may
actualy work better with a slow quenching gap, I think.
>However, the way I understand resonant rise (maybe this is incorrect ??) is
>that the output energy of the coil will be greater than what you "stuff" into
>the primary. This would violate the energy conservation laws and I donīt see
>how this is possible.
Its not.
>I can not see how you can store a charge on the coil (alone).
The coil is an inductor. Imagine a shorted inductor. Drop a magnet it in.
The changing magnetic field induces charge to flow, a current. The inductor
is now "charged" or "fluxed". If it is superconducting, there will be no
voltage drop across it as the current flows in the loop, forever. Now open
it! A large voltage appears across the break in the current loop, limited
only by capacitance or gap breakdown. How do you explain this 'opening'
voltage?
>The way I read some of the answers is that you can store a charge on the coil
>itself (which has to be a very small amount).
You could store megajoules of energy in a large enough inductor with its
current & magnetic field. There is no 'charge' visible until you break the
current loop. Magnetic materials typicaly store 10 times the energy of
capacitor dielectrics. But not quite as much as chemical explosives :(
>Another one of my question to the "resonant believers" is:
>
>If resonant rise does occur, why doesnīt the output (spark length) of an
>unloaded (!!) coil continue to grow the longer the coil operates? Of course
>there would be a limit to this, but any (unloaded) coil should experience
very
>short streamers that will (have to) grow in length the longer the coil
runs. I
>have never seen this happen.
You cant see it happen fast enough. After a few hundred microseconds or a
few milliseconds with realy big coils, the losses equal the rate energy is
input. After this time additional energy just heats the coil's resistance &
other losses. This is why impulse coils perform better than CW coils.
>What am I missing I.e. why do some guys (even experienced coilers) say a TC
>encounters resonant rise?
>More confused than ever before,
I started off learning that transformers were like electronic levers. The
problem with crude analogies like that, are they don't explain "flyback",
resonant rise, et.
Read a good book, like the "ARRL Handbook" to find out what inductors,
current and magnetic fields are. Then get a free SPICE simulator, then do AC
and transient analysis. You will learn something.