Re: Big Spark Induction Coil

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

Original poster: "Kurt Schraner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <k.schraner-at-datacomm.ch>

Hi Godfrey,

Thank you for your kind words about my inductor. I'm well aware, larger
induction coils beeing around, and even in past days really impressive
ones: probably you too have seen the one on Lyonel Baum's 1'000'000 V
site: http://hometown.aol-dot-com/lyonelb/index.html . The "generating
spark" part of my coil would be able to produce >one foot sparks as well
(..as was my plan, I confess ;-P ), but insulation problems limit the
normal use to ~20cm (8") realistically. Otherwise the partial/normal
discharges will lead to premature distruction of the insulating
materials.
Design and building: my idea of a rational design method was probably
similar to yours: I wanted to start with some reliable equations. At
this stage, our friend Dr Duncan Cadd was unselfishly helping with tips
and some literature (thank you "Dunckx"!). Him too knows, regarding my
design and building: "The weather was before the prognosis" ;o). It was
initiated by scrounged materials: the available ironcore, the primary-
and secondary wires. Then: coiler-buddy Andi's experience and our common
problem solving attempts with his inductor. And my "belly". One thing
was clear: I wanted to make an induction coil for itself, not i.e. as a
power supply for a TC. 30cm (1')spark was a goal. The 30cm sparks were
not achieved, but it turned out: I'll be going to consider the inductor
for a "very HV primary, little TC" power supply, 'cause it makes so
brute little cap discharges =;o)... 
My, hopefully coming, "theory" notes, will not satisfy the well
justified need (OK: by geeks only!) of a scientific design procedure.
I'm just testing, how the only available theory of a lossless induction
coil, which I'm aware from, by A.Bouwers, in his book "Elektrische
Hoechstspannungen" (1939, Springer), is compatible with the information
from my experiments (yes, it is...!). However Bowers's theory has small
flaws, and is to be "rediscovered" by my own reconstruction of his
derivations, which are shown with large "gaps" only. Soo..., this will
be more of value to analyze existing coils, like i.e. ignition coils,
than for the design of new ones. It evaluates coils, when L1,L2 and k
are known, as is the case for the simulation models, when additionally
the resistive parts R1,R2 and Rfe are assigned.

Might be, Bert, by grabbing his bottomless knowledge - and ability to
explain, together with his immense library, could bring up something, we
are not yet aware of, about induction coils? 

However, when I was quite mid in the building process, a reprint-copy of
the book:
"Induction Coil Design" by M.A.Codd, E.& F.N.Spon Ltd.,London
Haymarket,1922, which I ordered from PV-Scientific:

http://people.clarityconnect-dot-com/webpages2/arcsandsparks/reprintpage.html#HVPA

arrived. It's a really nice book about the subject, with a bunch of
practical info, - even a number of measured and interpreted waveforms -,
and indeed a stepwise procedure for the design of induction coils. If
translated a little to the contemporary magnetic materials, power
sources and, perhaps, interrupter possibilities, this might be just what
is the need, and even without: a great approach! I've much respect, of
what those "old guys" were able to do, without computers and modern
electronic gear for measurements. And without modern plastics for
insulation. Unfortunatly the book was copied rather carelessly, or
either edited careless in the original: many waveform oscillograms in
mirror image, even missing graph, all photographic repro's only 2 color
B/W (no grayscale). - But in the whole: of good value to the amateur -
anyway. Please contact me off list, if you need more info. 

...Yes, if we build an induction coil, we want to "hit", but it cannot
be too critical IMHO!

Cheers,
        Kurt Schraner

Tesla list wrote:
> 
> Original poster: "Loudner, Godfrey by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>
> 
> Hi Kurt
> 
> Your homebrew induction coil is really cool. When I was a young teen, a EE
> professor gave me one that was larger than your homebrew outfit. It was used
> in classes on transmission lines. The spark would jump over a foot. I don't
> have that induction coil anymore. Maybe I can get it back by building a
> scaled up version of your outfit. I think I have the materials in storage.
> I'll be eagerly awaiting your theory notes so I can begin a design. I always
> wanted to build one, but there seemed to be a lack of design procedures in
> the literature. Perhaps your theory notes will eliminate the time consuming
> hit and miss method. After winding that many pancake coils, you want to hit!
> 
> Godfrey Loudner
>