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Re: Induction heating in toroid / short circuit of secondary
At 01:15 PM 12/25/1999 -0500, you (Richard Wall) wrote:
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>
>In a non-discharging disruptive TC, fields at the termination (top) of the
>coil are almost exclusively "elecrostatic" or electric if you will. Current
>and and magnetic fields are nil. This can be demonstrated experimentally.
>There is really little magnetic field at the top of the coil with which any
>shorted turn toroid magnetic field may interact.
A VERY good point!! I ran some numbers for my coil which "suggest" (the
programs were never meant to be used for this situation) that the coupling
of the secondary to the toroid is 0.05. However, the current near to top
of the secondary decreases dramatically reducing the effective energy that
would go into this shorted turn. I would "guess" down to near 0.005.
There is not that much magnetic field up there to get shorted. The
conductivity of the toroid is probably pretty poor for an oxidized,
corrugated, dented, and duct taped aluminum donut. Not that much energy is
really going into heating it...
>
>There are huge alternating electrostatic fields though. Despite the term
>"static" these very high E field potentials are varying in reference to RF
>ground from positive to negative every 180 elecrical degrees. The vast
>majority of coilers are under the mistaken impression that energy of a
>single polarity (similar to a van deGraf generator) is built up and stored
>in the toroid. And, after reaching sufficently high potential a discharge
>is initiated. Not so, the toroid is a very busy place with polarity
>changing from positive to negative and back with refernce to RF ground at
>the resonating frequency of the Tesla coil. There is resonate rise and
>positive-negative potential swings may reach hundreds of kilovolts before
>breakout occurs.
You betcha!! My plane wave antenna's show this but it is hard to impress
on those without such "toys" the tremendous fields that exist near these
machines. Electric fields of 200kV per meter at the Fo frequency are very
typical and often exceeded.
>
>During the heyday of electrostatics, indeed, all known electricity was
>"static". During Franklin's day the only "dynamic" electricity that occured
>was lightning. Subsequently as electrodynamics evolved electrostatics was
>almost forgotten and became a curious electrical relic. Describing
>"electrostatic" electricity as dynamically changing is not an oxymoron. As
>it turns out, "static electricity" may (or may not) have a dynamic componet,
>but not in the well known EM model. I know using the older term "static" in
>a dynamic sense may be confusing, but think of an electrical field where
>only the amplitude of the *potential* varies with time. There is no
>associated magnetic field. There is no movement of charge, current or
>magnetic flux.
Static electric fields are alive and well just in a different form (like
computer memory). I always talk of "electrostatics" when I really mean
"electrodynamics"... :-)
>
>Experiments abound to demonstrate these dynamically changing electric
>fields. These simple experiments are designed to detect varying electric
>fields unassociated with magnetic fields. It is very important to choose
>proper instrumentation that will only detect either the electric or
>magnertic field and totally reject the other. For ES instruments choose
>very high input impedance instruments (teraohms for some ICs is good) and
>high CMRR (> 90 dB) to eleminate common EM signals. I build most of my own
>from precision differential instrument op amps. A good cheap source is
>Burr-Brown from Digikey. Others like Richard Hull use high grade
>electrometers such as Keithley. Richard has also designed a cheap
>electrometer which I believe he has placed in the public domain. See
>HVlist. Older ES volt meters also work great. Absolutely no EM with these
>machines.
>
>For magnetic field instruments I use small coils, either air core or wound
>on ferrite cores. I have used Hall IC devices. There is also a
>magnetometer IC by Philips for under $20, but I have not used this one. Of
>course, the SQUID is the most sensitive magnetic field detection device, but
>few of us will ever see one.
>
>Here are a few very simple, but powerful, experiments you may wish to try.
>Remember it is imperative to know the reference point from which you are
>measuring each and every time.
>
>1. Wiggle wand experiments made famous by Charles Yost. While an
>electrometer is nice, I have done this one with a ball electrode receiver
>and an oscilloscope. Simply electrostatically charge a plastic rod and wave
>it to and fro in front of the "receiver". By varying the distance between
>charged bodies the ES potential varies between them. Coulomb's law of
>course, but there is no doubt that the amplitude of the ES potential varies
>dynamically. There is no magnetic component.
I would suggest a few transient protectors incase there is an arc. A B210
is a terrible thing to waste if the charge gets transfered to the input of
the scope. But the B210 could probably survive...
>
>2. Place a disk on a variable speed motor. Attach either a magnet or a
>charged dielectric that is counter weighted on the other side of the disk.
>If a charged capacitor is used be sure to have one plate on one side of the
>disk and the other plate on the other side and measure on opposite sides.
>Remember always be sure of the reference point. This is a variation on the
>wiggle wand experiment, but a sine wave can be received on an oscilloscope.
>Both the magnet and charged dielectric (ES) waves are dynamically detected
>but only with their appropriate detector -- never both EM or ES on the same
>type detector.
Within the last six months, Scientific American had an Amateur Scientist of
an "Electrostatic Mill" which may be of similar interest.
>
>3. With a variable HV DC power supply carefully charge a HV capacitor lead
>while measuring the other plate electrostatically (no direct connection).
>Remember the reference point. Varying the charging rate of the dielectric
>varies the ES potential on the opposite plate. There is no detectible
>current moving through the dielectric even using the most powerfiul SQUID
>device. BE VERY CAREFUL with this experiment and be sure to fully discharge
>the capacitor afterward.
>
>4. Measuring TC and van deGraf generator ES and EM potentials with these
>instruments is most interesting. Who can deny that a van deGraf is anything
>but an electrostatic machine and seeing the top potential dynamically
>increase is experimental proof that changing ES potentials in fact may vary
>dynamically? A significant amount of data may be amassed in this way
>regarding both EM and ES fields, their interactions and dynamic nature.
>Terry's fiber optic system makes this type of experimenting immeasurably
>safer.
When I started to work on measuring TC voltages and currents, isolation and
getting the expensive instruments far far out of the way of the Tesla
coil's "killer fields" was an obvious priority. Fiber optics has proven
perfect for this task. I (and Finn ;-)) have blown a few "hot side"
transmitters up but the real equipment is totally safe at the other end of
the 10 meter glass fiber...
>
>So what? What good is an outmoded form of electricity in this modern day
>and age? Ever hear of vacuum tubes, CRTs, oscilloscopes, linear
>acelerators, CMOS, MOS, FETS, MOSFETS, IGBTS, ES copiers et cetera, et
>cetera . . . ?
>
>Now Tesla Coils?
Tesla coils being the obvious "important" use here ;-)))
>
>
>Have fun experimenting and be safe.
>
>Happy Holidays,
>
>RWW
Always good to hear from you Rick. I always wonder what your up to ;-))
For those that don't know, Rick was my very first "customer" for the fiber
optic probes (waaaay before the rest of you ;-)). His first system was
where all the real design, development, and sweat was done for the modern
version. Rick's interest in the fiber probes was very important in keeping
me going at that time and I sincerely thank him for that!!
Cheers,
Terry
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