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Re: helix vs. flat-spiral primary

Hi Dan,
    As for the exact shape of the fields, I'm not sure, but I do know that
helical primaries are mainly for low powered coils with high height/diameter
ratios; and I imagine it would have a more vertically extended field.  They
provide more inductance and are closer to the secondary and discharge
terminal than flat pancake primaries so they are more apt to saturate the
secondaries- or be struck by them.  Not that helical primaries are bad, the
proper TC can be suited to any Primary type.
    Most coilers use either the flat primary or the inverted cone primary,
which is a cross between the two.  The inverted cone primary appears as
follows, and varies in steepness from usually 15-45 degrees depending on the
amount of desired inductance (greater angle = greater inductance).

\                              /
   \                        /
      \                  /     x degrees
         \            /_______

    The flat primary, for higher powered coils and lower height/diameter
ratios (3:1,  3.5:1), I imagine would have a not as laterally extended field
as the helical primary, and the flat primaries benefit from the extra
distance from the discharge terminal (crucial for Xtra long arch lengths of
3X or more the secondary height).
    I believe (open for criticism) the significance of the proposed field
shapes has to do with the theory that secondaries carry a larger current
near the base of the coil, and a larger voltage at the top.  Then the
height/diameter ratio would have to correspond with the lateral extent of
the electromagnetic field-- top of coil = top of field-- and the intensity
of the field would correspond smoothly with the intensity of the current in
the primary.  So unproportional height/diameter ratios and
field-height/field-intensity ratios would produce less efficient arcs.
    If you don't already have it, the WinTesla program found at
http://www.velocity-dot-net/~djb/files.shtml will calculate the inductance, wire
length, and a bunch of other useful information about the primary (and is
also a great program for the whole TC in general, I highly recommend it) if
that will help you at all.  Hope I have shed some light on the subject
                ~happy coiling




----- Original Message -----
From: "Tesla List" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, March 13, 2000 1:25 PM
Subject: helix vs. flat-spiral primary


> Original Poster: "Dan Kline" <ntesla-at-ntesla.csd.sc.edu>
>
> Hi all,
>
> I'm wondering a little about how magnetic field shaping of the primary
> might affect the coil system...
>
> (excerpts from other emails):
>
> "A flat spiral, (it seems), might affect a smaller
> region of the secondary, but with a much denser field. A sharp pulse to a
> few secondary turns, rather than a "thin" wipe to a lot of turns, like a
> helix might do. Things might be more efficient that way."
>
> "I'm thinking of it sorta like this: If I have a drum, and I hit it with a
> drumstick, I get a sharp "rat-tat" sound. If I hit it with one of those
> leather chinese-gong hammers, I'll get a softer, more "mushed" sound. The
> enery transfered would be the same, but I'd get different outputs of
sound.
> I was thinking that the narrower field of flat spiral primary would be
like
> the drumstick, and the helix would be like the soft mallet. Or it might
not
> matter at all. I just got this idea from trying to visualize the magnetic
> fields of the different-shaped primaries."
>
> Comments anyone?
>
> Thanks,
> Dan
>
>
>
>