RE: double wound secondary (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 3 Oct 2007 13:50:24 -0400
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: double wound secondary (fwd)

No!  Inductors in parallel do not add.  If they are tightly coupled and
identical in value, the net inductance approaches that of a single coil.
If the two identical tightly coupled coils are wired in SERIES, the net
value then approaches 4X the individual value.  If the series coils were
not coupled, the net value would be 2X.  See
http://en.wikipedia.org/wiki/Series_and_parallel_circuits

Gary Lau
MA, USA

> From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: double wound secondary (fwd)
> 
> Hi Dave,
> 
> The Q isn't as neat (in my little book) as the inductance. The only
way
> possible I can account for this is if the two windings at the bottom
and
> top are in parallel and very close proximity. We know inductors in
> parallel add. But, when current is flowing and if the two inductors
are
> in "that" type of proximity (and position) winding for winding, then
we
> now have the currents in both inductors doubling up on the flux (the
> density is double on both windings). This would certainly result in a
4x
> (or about) inductance. I've never done that with a coil, but from an
arm
> chair physics view, it makes perfect sense that you would have 4X the
L.
> 
> One of the goofy things not always realized with the multiturn coil
> formula's (air core or otherwise) is that that a series connection is
> assumed. You must have 2 parallel wires in this type of close
proximity
> to achieve this. Very cool!
> 
> Take care,
> Bart
> 
> >---------- Forwarded message ----------
> >Date: Tue, 02 Oct 2007 01:32:13 +0000
> >From: sparktron01@xxxxxxxxxxx
> >To: Tesla list <tesla@xxxxxxxxxx>
> >Subject: RE: double wound secondary (fwd)
> >
> >Antonio
> >
> >Gary Weaver has posted several times (and I have built) a "multiple
layer"
> >coil that is not specifically a bifilar wound coil.  Wind one layer
_close
> >wound_ then wind another layer on top of and in "groves" between
adjacent
> >turns of lower winding layer.
> >
> >By careful arrangement of individual wire entrance and exit into
windings,
> >maximum winding error of only +/- 1 turn (much less is practical)
will
> >occur.
> >
> >I have wound such a coil with two layers, and have noticed a MUCH
higher Q
> >then a typical "bifilar" wound coil.
> >Inductance is ~4X higher to boot.  In this case, it is equivalent of
two
> >coils close wound in parallel, R would approach
> >R/2 (proximity effects will make it larger, but still significantly
less R
> >then a single winding coil).
> >
> >Band pass testing with two winding coil revealed a bandpass so
narrow, I
> >could not fine tune VFO to maximum response, it would "jump" either
side of
> >response peak.  Gary noticed large improvement with two windings in
> >parallel, less improvement from 2 to 3 layers in parallel.
> >
> >My coil was used on a VTTC powering a CO2 laser.
> >
> >Regards
> >Dave Sharpe, TCBOR/HEAS
> >Chesterfield, VA. USA