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Re: Racing Spark Prediction

Original poster: dest <dest@xxxxxxxxxxxxx>

Hallo Terry and other (if any : D) interested parties : )

> Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

> "I" don't quite understand racing arcs either.  I used to think it
> was do to pure transformer action when the coupling is close.  A ten
> turn primary at 20kV vs. say 400 turns in the lower 10 inches of a
> coil form.  That might push 800kV into a 10 inch section.

do you really think so? then let the bass kick, Terry : D

let`s take one arbitrary secondary, say 72cm long - not too small and
not too big, sorta "average", yeah? : ) let H:D ratio would be 4:1 -
again, sorta "average", or "real" thing, so OD of the secondary
would be 18cm. about number of turns - i have approx. 2 kilos of
0.46mm enamelled copper wire here - let`s wind it on this baby, to get
1565 turns exactly. the secondary would have about 98mH - sorta
"not bad" i think : )
hey - it have 552 turns "in the lower 10 inches of a coil form" - just
like you wish and even better : D
now all that you want is "A ten turn primary at 20kV" - no problemo at
all - just take 1cm OD copper pipe and wind those 10 turns. to make
things even much more worse, wind not flat but solenoidal primary
instead, 15cm hight, OD is 28cm only, so you would have only 5cm of
clearance between pri & sec - do ya like it? i do, coz it gives the
coupling about 0.307 - i hope this "is close" enuf for ya? : )

now, the voltage that primary inducing in any part of the secondary is:

v2 = v1 * k * sqrt (Lsec / Lpri), or:
v2 = v1 * M / Lpri

where M is a mutual inductance between whole primary and that part of
secondary, so to compute voltage distribution across the whole
secondary, caused as you said by "pure transformer action" we need
just compute M with step of say 2.5cm and i did it for this "coil" -
it took about 15 minutes only : )


so what can we see here?
nobody does classical coils with k=0.3, nobody wind primaries so close
to secondary, but even in this "extreme" conditions "A ten turn primary
at 20kV" just CAN`T "push 800kV into a 10 inch section (400 turns in
the lower 10 inches of a coil form)".
all that can happen it`s only about 320kv in lower 10 inches of a coil
form - that`s only about 12.8kv/cm, and the absolute maximum is about
16kv/cm - in first 5" of a coil form.

so "pure transformer action" in what you (and probably some other
people) believes it`s just another "coilers" myth : )))

anybody can easily verify all my calculations step-by-step in 15 min.:

1. mathcad 7 file for this coil is here:


2. inca model for this coil is here:


3. inca program itself is here:


you don`t need brains (only calculator) to check this : D

just arm-chair cowboy shooting in the dark : )