Re: flat coil ?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Chris Swinson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <exxos-at-cps-games.co.uk>

Hi Paul,
> With 45" and 316 turns, I get around 40mH, rather than 44mH, so
> something is not quite right with your count or dimensions. You'll
> need to make sure that your outer diameter is given accurately, and
> as Bart says:
>
> > It would be good to know the inside diameter as well.
>
> And perhaps you could also measure the DC resistance of the winding?

Inside dia is 2".  DC resistance is 5.2R.   I will re-count the turns though
it maybe be only 1 or 2 turns from what I counted before, makes my old eyes
hurt after about 100 or so ....



> For the rim-grounded center-hot configuration, the Fres is now
> around 160 kHz.  Voltage and current distributions are in
>
>  http://www.abelian.demon.co.uk/tmp/cs1r.vi.gif
>
> in which 0% position is at the rim and 100% position is the center.
> The highest stressed part of the coil, for both current and voltage,
> is around 10% to 15% of the way in from the rim.  The point marked
> 'inflection' is the place where the voltage gradient is highest.


In a few days I will test the frequency on my scope. It will have to be when
its all varnished else moving it could be fatal at this stage..




>
> Chris wrote:
>
> > Would I expect the flat coil to work better than a tube
> > wound coil ?
>
> Not necessarily.  One feature of the flat coils that stands out,
> especially for the center-hot arrangement, is that the effective
> inductance at resonance is quite a bit higher than the DC
> inductance, whereas for solenoid coils the effective inductance is
> usually a little lower than the DC inductance. So you get a little
> extra inductance for free, so to speak.  In your case, Ldc is around
> 40mH and Les is around 50mH.  This might mean that you could get a
> little higher efficiency from the primary circuit, but I'm not
> convinced that the difference would be noticeable.  Set against
> this possible benefit is the extra difficulty of winding the flat
> coil, and the possible problems of premature breakdown in the outer
> 25% of the winding, and between the central 'topload' and the coil.

Values may alter slightly when its all varnished. At the moment some turns
dont seem to want to stick down to well so the reading could be slightly out
anyway.  I sure prefer winding tube coils, flat coils are a pain to say the
least, actually after about 50 turns the coil stops spinning and the room
starts to spin :-\

>
> My guess is that you may end up with a more efficient coil, but one
> which will take less maximum power, than the same wire wound into
> a solenoid.  With this in mind, the flat secondary may find its
> niche as a CW secondary or tertiary coil, in which the high Les and
> high transfer impedance can be exploited in the presence of modest
> peak powers.  There is a dearth of measurements on this type of coil,
> hence our interest in your efforts.
> --
> Paul Nicholson
> --

It will be interesting to see how it actually works.  I will compare it to a
tube wound coil and do some tests. The flat coil may well have a few more
turns as I think it was worked out to 44" in dia not 45" like it is, though
I started off a little wider in the centre ( 2" ) so the wire length
*should* be about the same as my tube wound coil. While I think about it,
has anyone any ideas on how long the primary will need to be ? 3 or 4 turns
should do it though I don't want to wind 4 turns to find out I actually need
5 or something silly. The primary tank is 12nf 10KV 50ma. I guess 5 turns
should be about right for this... tune point should be about turn 3 going by
my 3foot primary..

Chris