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RE: Racing Arcs Explained???

Original poster: "Garry Freemyer" <garryfre@xxxxxxxxxxx>

I read some of the posts about racing sparks. There is a LOT of math in
there and math isn't my forte, unless it involves translating formulae to
programming language.

I did have an event that I thought MIGHT explain racing sparks ...

I had to repair a secondary coil that originally had AWG 24 and the closest
I had was 28 gauge.

I decided to rewind it with the 28 wire, calculating that I had to shorten
the winding area by about 7 inches, and so I did, running the end up to the

It seemed as if, the sparks tended to emit from the end nodes of the
resonance point on the secondary, namely the top winding rather than
traveling up to the toroid.

On running the coil, sparks shot not off the toroid as I expected, but off
the top winding.

Proving the one observation that having the entire secondary too close to
the primary winding, can result in racing sparks.

I asked myself, why would close proximity cause racing sparks? Answer:
Because a spark gap primary emits many harmonics of the fundamental
frequency and these frequencies tend to be weaker than the fundamental
frequency - spark gaps being rather chaotic in frequency compared to solid
state or tube units. The closer coil might pick up some of these harmonics
to some extent and the resulting energy might tend to emit from nodes along
the primary instead of the top load.

But what about coils that have racing sparks where the distance between the
primary and secondary is appropriate?

I remember my ham radio studies, where I created a dipole antenna of a
certain length where it would resonate with the frequencies I wanted to
transmit, one at quarter wave, other at half wave, then five eights,
depending on the frequency. It worked really well.

Now, suppose we have a unipole spark gap coil and the distance between the
primary and secondary is correct where the gap is creating a fundamental
frequency and several harmonics and the secondary just happens to be of a
length that both resonates at the fundamental frequency and one or more of
the harmonics. It seems possible that the secondary may be resonating on
both frequencies and one of those frequencies is creating the racing sparks
because the node for that frequency might not reside at the top load but
along the secondary.

It might also explain why racing sparks might occur on a clean secondary
when the unit has not been properly tuned. The unit is so out of tune, its
picking up harmonics and amplifying them to the point that racing sparks

What might be done to avoid this problem in spark gap coils aside from maybe
using chokes to filter out the harmonics? My idea is that when designing,
determine your frequency, but make sure that the secondary is not of a
length that might also resonate at one or more of the harmonics. Such as a
secondary that harmonizes at the fundamental frequency as a quarter wave,
but works as a half wave at a harmonic. Perhaps a oscilloscope or other
device to find the frequencies emitted beforehand and then plan accordingly.
I have my doubts that this will work however because the secondary can
effect the primary and I wonder if a coil can be constructed where the
secondary will only resonate at the fundamental frequency and not any of the

This guess on my part seem more clear to me than all the formulae but that's
my problem - I should have kept my calculus skills honed. :)

This guesswork of mine might be supported if it was found that tuned solid
state and Vacuum tube coils don't suffer from this problem.

So, the question is, has anyone ever experienced racing sparks on a tuned
solid state or VTCC? If they occur on these type of coils and if these coils
don't emit harmonics, it would disprove my guesses.