Re: Space winding

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ken,
        I think I spot a problem:

On 11 Aug 00, at 18:25, Tesla list wrote:

> Original poster: "Kennan C Herrick" <kcha1-at-juno-dot-com> 
> 
> I'm a bit reluctant to continue commenting on this subject:  Although I'm
> an E.E. college-graduate, it was 50 years ago & many of the details have
> long gone.  However...
> 
> First, I repeat the tabulation & commentary given recently by Mark S.
> Rzeszotarski:

<snip> 
> Now...my comments:
> 
> 1.  Secondary Q = wL/R where w=2 x pi x resonant frequency, L =
> inductance & R = effective resistance.  Also, L is proportional to n^2,
> the square of the quantity of turns, other coil-shape factors being
> equal.
> 
> 2.  From the tabulation, R diminishes, due to diminished
> proximity-effect, by 1/2 for a tabulation-"w" of 0.5; that is, for the
> case where the space between turns = the wire diameter.
> 
> 2.1  But for that case, n has diminished to 1/2 of the prior quantity and
> so L diminishes to (1/2)^(1/2) or .25 and also, ohmic R diminishes by 1/2
> since the total wire length is 1/2 of what it was.

Why should n have diminished? Are we not talking about the 
same number of turns?
 
> 2.2  Thus, it would seem, total effective R will have diminished to 1/2 x
> 1/2 = 1/4 of that for the close-wound case.  And thus, the new Q becomes
> 0.25/0.25 of the old Q, or just the same.

I have a set of measurements which shows that for the same 
diameter, height and number of turns, a spacewind produces a 
higher Q coil. I put them to the list about give years ago. 
  
> 3.  The ultimate voltage developed in the secondary prior to a spark is
> going to be directly proportional to n and also to Q, given a big enough
> top toroid.  (I differ with Dr.  Rzeszotarski's assertion that the Q is
> "killed by the primary":  During the time of voltage build-up prior to
> the spark, the higher the Q the higher the voltage--given a large enough
> top toroid.  Once the spark commences, the secondary's Q does become
> immaterial, because of the major loading by the spark.  Then,
> power-delivery from the primary becomes important, in maintaining and
> lengthening the spark.  So, one might more properly say that the Q is
> "killed by the spark".)

If Q is infinite, output voltage is going have a definite 
limitation because the secondary is being supplied with a 
finite amount of energy. As Q climbs higher, the law of 
diminishing returns is at work. 
     Perhaps one might consider this to be all academic as 
there are many fine coils out there both closewound and 
spacewound. My view is simply that I can build a fine coil for 
lower copper costs and of a lower weight by using a spacewind 
with smaller wire.

Regards,
Malcolm

  
> 3.1  Thus, the 50%-space-wound secondary voltage is going to be 0.5 (the
> new n) x 1 (the same Q) = 0.5 times the close-wound voltage.  From this I
> would conclude that tightly-wound is best, absent any problem due to
> turn:turn sparking.
> 
> 4.  >However<...consider this:  With secondary n diminished to 1/2,
> perhaps 2x the current can be delivered into the secondary from the
> primary >after< the spark starts.  That doubled current will act to
> fatten and extend the spark to a greater degree than where n was not
> diminished.  That effect may or may not overcome the reduction in initial
> spark-voltage to 1/2, in producing a satisfactory spark.
> 
> So where do we stand on this?  Will it or won't it?  Who out there can
> properly quantify all this?  Or correct me if I'm wrong?
> 
> I'm in the process of space-winding a 12" x 48" Sonotube-secondary. 
> Perhaps I'll finish that and then make another exactly the same except
> close-wound, & compare the two  (With my self-tuned solid-state primary I
> will be able to do that as quickly as I can swap one for the other; all
> else will remain exactly the same.).
> 
> Ken Herrick
> ________________________________________________________________
> 
> 
>