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The IDIOT is gone
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The IDIOT is Gone!
My thanks to all of you who responded to the Idiot Guide postings with
material, questions, constructive criticism, and moral support.
A few people voiced the opinion that the title "Idiot's Guide" might
actually make people shy away from the project and either not contribute,
or not be interested in actually reading it (I guess for fear that someone
might think that only an idiot would read such a thing).
The point is well taken, and so I will be dropping the title. Don't know
yet what the final title will be, but for now, how about if we all refer to
it simply as the Guide. I hope that ends that set of objections, and that
all of you who have been holding back because you wanted nothing to do with
Idiots will now reconsider and participate.
Also, some objected to my unconventional use of capitalization, and I agree
that a more conventional approach would be to everyone's benefit.
So far the Guide includes the revised text from the original "Idiot's
Guide" postings with all the capitalizations normalized and with the
inclusion of all suggestions made by Malcolm Watts and Richard Hull and all
the others who wrote asking me if I could include this or that.
I hear you, guys, and I want you to know that I APPRECIATE your input. This
is OUR project, and I will always strive to be responsive to the input you
give me, because ultimately it is ALL of us that benefit from such
constructive criticism.
I see a real need for a Beginner's Handbook that is not too heavy on the
math. I want to help
get people HOOKED on Tesla coils. Tesla coils are the kinds of things that
often trigger in people a lifelong interest in science. I think that for
most of us who are here on the Tesla list, we have very fond memories of
our first encounter with the Tesla coil, no matter at what age we first
encountered it. I don't want a Beginner's Guide to turn people off
because they see all the math and say "Oh, that's too hard to understand...
I'll just build a Van de Graaf Generator for my science project instead of
a Tesla coil."
BUT, you are ABSOLUTELY right that we need a Handbook for those persons who
really want to get into coiling in a big way, or who are already coilers
and just want to have a better understanding of what is going on BEHIND all
that noise and sparks. This group need a lot of math to help them decide
how many turns, what diameter and length, how far apart, what resonant
frequency, and all that sort of Good Stuff.
The Experts out there also deserve a handbook that THEY can use. A
place where we can gather all of the information that is currently
available, all of the references and formulae, and the theories and
conjectures and opinions that make coiling a living, breathing thing, not a
dead body of information.
I think that if we begin by trying to make the Guide as complete and
comprehensive as we can about every single aspect of the Tesla coil and all
its component parts, we will be on the right track. From the COMPLETE
Guide it would be relatively easy to snip out the stuff that would
confuse a beginner, and end up with a beginners handbook that is derived
directly from the complete guide.
The Complete Guide would optimally have a companion Book of Diagrams and
Formulae useful to the coiler. The TEXT would then explain what was going
on, and notations would direct people to the appropriate page in the Book
of Formulae to get the actual formulae.
Thus a typical entry might look
something like this:
*** Beginning of article
MATCHING THE IMPEDANCE OF THE TRANSFORMER AND THE CAPACITOR
This section discusses material that affects the efficiency of operation.
It also affects the quality of the spark produced at the spark gap.
By carefully matching the impedance of the transformer and the capacitor,
the efficiency of the circuit can be improved. Matching will allow us to:
a) Get maximum delivered power from the transformer.
b) Use the smallest capacitor necessary to store the power delivered by the
transformer.
The transformer secondary winding has a characteristic impedance at 50/60Hz
that will limit the maximum current that the transformer can deliver. You
can model the transformer as a perfect voltage source in series with an
inductor and a resistor. The resistance is caused by
the length and diameter of wire used in the construction of the
transformer's secondary. The inductor represents the inductance of the
transformer secondary, which causes its AC resistance at 50/60Hz. {Fig ??
Eq ??}
Methods for measuring actual transformer secondary impedance are given in
{Ref Transformer Sec ??}
The current available at any given instant from a given transformer is
limited by the transformer's instantaneous voltage and total effective
resistance at that instant.
If a capacitor and an inductor are connected in series, and if the
inductive reactance and the capacitive reactances are made to be equal,
then the effective total reactance equals ZERO. For a given inductance and
capacitor, this will occur at only one particular frequency, known as the
resonant frequency. {Eq ??}
Note: Some authors prefer to refer to this as the anti-resonant frequency,
because at this frequency the overall Series Circuit resistance is at its
Minimum. In a Parallel Resonant Circuit the resistance is Maximum at
Resonance.
Note: Do not confuse this 50/60Hz resonant frequency with the resonant
frequency of the RF portion of the Tank circuit, or the self-resonant
frequency of the secondary.
You might object that it doesn't LOOK like the transformer and capacitor
are in series, but they are. That is because we can consider the circuit AS
IF the transformer was a perfect voltage source in series with a resistor
and an inductive reactance, and the capacitor as if it were a perfect
energy storage device in series with a resistance and a capacitive
reactance.
At Resonance the circuit reverts to acting like a perfect voltage source, a
resistance, and a perfect energy storage device connected in series,
because at resonance the reactances cancel. At resonance the transformer is
able to transfer the maximum current possible to the capacitor.
If the Spark Gap were to fire at the instant the above mentioned Maximum
voltage was reached across the capacitor, then the system would be firing
at a point where optimum energy useage was being achieved.
It has been shown that for optimal efficiency (and operation) the power
capacitor's capacitive reactance should be equal to the inductive reactance
of the transformer. When this is done the capacitor's capacitance rating
will be the smallest value possible that will allow that particular
transformer to transfer the maximum possible charge within a given half
cycle. {Eq ??}
If the inductive reactance of the transformer is greater than the
capacitive reactance of the capacitor, then this results in a lower maximum
voltage appearing across the capacitor, with resultant reduction in the
total charge transferred to the capacitor during the charging time. The
capacitor is under-utilized. This means that the capacitor is actually
larger and more expensive than it has to be. The Tesla coil will work, but
efficiency is lower than it could be.
If the inductive reactance of the transformer is less than the capacitive
reactance of the capacitor, then the transformer will cause the capacitor
to reach its maximum voltage early in the charging cycle. In this case the
transformer is under-utilized. As we shall see later, this can create
excessive flame arcing at the Spark Gap. {Ref Spark Gaps}
{Prog ??: Transformer and Capacitor Matching}
Additional Remarks:
If RF chokes are introduced into the transformer circuit, then their
inductive reactance at 50/60Hz may have some effect on the total inductive
reactance, though it is generally small compared to the inductive reactance
of the transformer's secondary.
The RF impedance of chokes does not enter into this
discussion of matching, because in matching we are only concerned with the
charge cycle, not the discharge cycle.
The inductive reactance of a transformer's secondary may vary. This can be
due to such things as Saturation of the core, or the inclusion of
resistances and/or inductances in the PRIMARY circuit. This is especially
the case with pole pigs, as they are often fitted with things like arc
welders and heating coils for use as ballast. {Ref Pole Pigs Sec 112} The
use of a variac will affect the secondary's inductive reactance, because a
variac is actually an autotransformer. With some of the larger Tesla coils
it may be adviseable to measure the actual inductive reactance of the
composite secondary rather than trying to determine it with a formula,
since some of the factors entering into play are not readily known.
Neon transformers sometimes have Power Correction, Magnetic Shunts, and
other features that may affect the actual inductive reactance. {Ref
Transformers}
If a transformer has been modified by removing magnetic shunts, then the
current rating will be greater than that indicated by its original
nameplate. {Ref Modifying Transformers}
*** end of article
The things in {} brackets would direct people to things like Equations {Eq
22,27}, Diagrams and Drawings {Fig 12}, related Sections {Sec 12}, and any
computer programs that perform the computations mentioned or implied in the
text {Prog 7}.
The purpose in such a plan is to keep the text eminently READABLE, even in
its pure text form. The person with more knowledge would not have to look
at formulae he already knew. A Novice would not be subjected to
mathematical detail that for him would only be distracting and confusing.
Experts could have more exact formulae that incorporate more detail
included in the book of formulae, following the formulae that might be
recommended for use by someone building a Beginner's Coil.
If you think the formulae should be placed inline, tell me so. We are just
beginning the process, and changes in style can be very easily made at this
point. A month from now it will be a very different story.
NOW is the time to make suggestions as regards the style of presentation!
The person who wanted the mathematical details would have it in the
separate reference book which he could have open as he was reading the
text. Ideally, the reference book would contain not only formulae, but
diagrams, a brief description of each formula, and references to their
application.
It would also be nice if the reference manual contained a dictionary of
terms used in the reference and handbook.
The reference book could contain program listings, or instructions on how
to use any computer programs such as TESLAC, etc. that are available. I
would envision a companion disk that would have the programs on them.
All of this would be available at the ftp site for downloading both in a
straight text form, and perhaps as a Postscript file. As more material
became available, we could add it to the existing files and upload it to
the ftp site.
As we begin to compile the Guide and its associated reference material, I
would put each of the Modules completed so far into text files at the ftp
site. These would contain the full text as it stands so far, and whatever
mathematical formulae that are referenced (that we have at that time). Note
that some modules will contain references to modules that have not yet been
written. In this case they will reference something like {Ref Rotary Spark
Gaps ???}
In the final version all these forward references would be replaced with
actual section numbers. If it turns out that a Module is referenced that
does not exist in the final version, then I would pull the reference
entirely. I include them initially so that people can see where I
contemplate having additional material on a subject placed.
The nice thing about using a modular approach is that as we finish each
module the members can download that little completed chunk and print it up
themselves.
Another nice thing about this method of presenting the data is that I can
write the text without worrying myself with what the exact formula IS, but
move ahead immediately with the explanations. Thus the text, even if
intially devoid of all formulae, can be easily amended to include as many
of them as are deemed desireable, through the process of getting YOUR
feedback on that module.
But that is also where I will be needing the help of knowledgeable people
like yourself. I might know that there IS a formula for computing the self
capacitance of a secondary coil, but I might not actually HAVE the formulae
at my disposal.
What I would LIKE to do is write up a section, something like the section I
showed above, post in to the list and then say:
1) OK, what do you think about this as a possible entry in the Handbook?
What is wrong? If you can, write what you would propose to put in
its place.
What is missing? Be as explicit as you can.
2) I need the actual formula for computing transformer impedance.
Someone on the list said Ztrans=Etrans/Itrans. Is that right?
Does that mean that a Neon with a tag that says 12KV -at- 30ma
has Ztrans=12000/.030 ? That seems AWFULLY High!
That implies that a 12KV Neon produces 30ma when you short
out the secondary and its voltage drops to ZERO.
That further implies that the Neon WASTES 360 Watts
when the current is 30ma. Can't be, can it?
Isn't the 30ma the rated continuous current.. and isn't
12000 the OPEN circuit voltage with NO LOAD?
(Or have I misunderstood the tag rating?)
I am more familiar with regular transformers, where
the power rating is the product of the voltage at
rated current, and the rated current.
Shouldn't the circuit be loaded down
until it produces the 30ma and then measure the voltage...
Then the difference in voltage from 12000 would be the
voltage being dropped ACROSS the impedance at a draw of 30ma
and the formula would now be:
Ztrans=(E1-E2)/I where E1=open circuit voltage (12KV)
E2=voltage at terminals when load draws rated current (Say 11KV)
I=rated current (.030 Amps)
****
Well, that should give you an inkling of the kind of task I have set out
for myself. I am willing to undertake it and give it my best. It will not
be easy for many reasons, but I honestly think that the process itself will
help all of us to think a bit more deeply about just exactly what IS going
on within our beloved Tesla coils.
I just hope it doesn't take forever to get people to cooperate. It is
impossible to do alone. I don't want to settle for pretty good. I want
something that will contain the BEST information currently available
anywhere. I think that the Tesla list members have maybe 95% of what we
need stored up in our collective noggins and notes Right Now. What I want
to do is get it all written down for all of us to use as a handy reference
book. A sort of Compendium of Knowledge on Tesla Coils, suitable for
beginner and expert alike.
As to Tesla Magnifier Coils, I am willing to include as much information
about them as I can get, and YOU deem desireable. I need to get my hands on
whatever info there
is already out there, but I am not finding very much. It would help if I
could get back issues of coiler newsletters and be put on the mailing list
for current issues. But I honestly cannot afford to subscribe to even a
few. And I am not yet fully aware of what exactly is out there. Perhaps if
the newsletters themselves were to give me issues in exchange for the right
to publish the fragments of the Handbooks as they come out. But you see, I
have already declared to everyone that this information can be freely used.
And I mean to stand by that. Anything less would be a disservice to us all.
By the way, I am posting the above section on Matching Impedances to the
list under the title "Guide 60HzMatch". I really need feedback on the above
circuit description.
I would like to start a Resource Module for the Guide that would include
things like what brand of varnish etc. our members have found useful. Some
of these items would have addresses, telephone numbers, etc. of suppliers.
For example, we might have an entry under Transformers something like:
Perfect Brand Neon Transformers
Members swear BY these, not AT them!
These are particularly resistant to internal arcing. Highly Recommended.
PolyWhatsit filling (not tar). Vacuum impregnated.
9KV -at- 30 ma $45
12KV -at- 30 ma $55
12KV -at- 60 ma $75
Perfect Brand Company
Address
Telephone / Fax
Pole Pigs
Try your local power utility. Most of these places have a graveyard where
they put older units that have been removed from service. Check your local
metal scrap yard.
New units can be purchased from ........ write to ........ for their
catalog #457. Typical price for a 14.4KV 10KW unit is $$$$$.
So, what do YOU think?
Fr. Thomas McGahee