Stacked primaries

• To: tesla-at-pupman-dot-com
• Subject: Stacked primaries
• From: Gary Lau 16-Dec-1998 2124 <lau-at-hdecad.ENET.dec-dot-com> (by way of Terry Fritz <twf-at-verinet-dot-com>)
• Date: Thu, 17 Dec 1998 11:29:56 -0700
• Approved: twf-at-verinet-dot-com

Richard Craven has published an excellent paper entitled: "DESIGN
IMPROVEMENTS IN TESLA COIL PERFORMANCE" on his web site, at
http://www.users.globalnet.co.uk/~craven/ieetesla.html.  One suggestion
made was in using two stacked primaries:

RC> As a result of using a higher impedance primary design, the resistive
RC> losses in the primary inductor are increased since more conductor
RC> length is needed to make a higher inductance primary.  This implies
RC> that the L/R ratio for the primary inductor needs to be optimized.
RC> Techniques are now employed whereby two Archimedean spiral primaries
RC> are stacked one on top of another. The mutual inductance M that
RC> exists between them is adjusted by varying the separation of the two
RC> coils. This removes the need for relatively lossy "tapping"
RC> connections and also minimizes the length of conductor needed to make
RC> up a given inductance. Thus the I2R or Joule losses are minimized. A
RC> further advantage is that there are no unused turns and this means
RC> that the coupling coefficient remains largely constant (less change
RC> in primary geometry) and there is no extra field stressing which
RC> would occur due to autotransformer action in the primary. 

I've never heard of this and can't visualize the electrical and mechanical
configurations.  Is there any more info on this and has it actually been
done?

Gary Lau
Waltham, MA USA

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