Re: space winding?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>

Robert Amaya wrote:

> Can anyone tell me what is the use of "space winding" the
> secondary and what are the benefits of doing this?

It may produce a lower loss coil.  For any given length/diameter
(h/d) ratio, there's an optimum spacing ratio that gives the
maximum Q factor:-

  h/d         Optimum spacing ratio
  1.0           0.6
  3.0           0.75
  5.0           0.85
  7.0           0.93

where spacing ratio is wire diameter divided by winding pitch.
(the above data from Medhurst, March 1947).

The effect on losses isn't huge, for example if a h/d 3.0 coil was
wound with a spacing ratio of 0.9 instead of the optimum 0.75, the
extra loss would be about 10%.

These optimum spacings arise from a tradeoff between proximity
loss and loss of overall inductance.

With a conventional TC, the secondary winding loss shouldn't be a
major factor and the above would probably only be a consideration
in a design for a high efficiency solid state system.

Extra spacing might increase the voltage breakdown capability of
the coil, but to see that benefit, I think the spacing would have
to be done carefully and consistently so as not to create a 'weak
link' somewhere.
--
Paul Nicholson
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