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,

>>>>>snip>>>>
> This arrangement only lowers the Fres to 154 kHz, and the entire
> primary is in a cold region of the secondary's E-field. Cpri = 55nF.
>
> But you wouldn't be advised to build a primary yet, not until you've
> decided what sort of a center terminal you'll use, and what the
> primary charging supply will be.  If you have a favourite primary cap
> that you want to use, let us know the value so that we can have fun
> inventing a primary to match.

The primary cap is 12nf, running on 10KVAC 25ma, I did state I think 50ma
before but that was a mistake, sorry...   I don't know what the center
terminal will be as yet.  It will proably be a short length of M10 studding
and I will bolt that though the center and fix the center turn of the flat
coil to that.  I haven't stated to build the primary yet, I think the room
is only 5foot wide and with a 4foot dia coil that leaves not much room at
all.  I will use the same copper pipe, I think it is 8mm dia. normally
spaced at 0.5" though due to limits on space I will have to try 1/4"
spaceing.


>
> As for top terminals, if you were to fix a small sphere on top of
> your center core, say 2" diam with center 3" above the plane, the
> Fres would only drop a little, to 153 kHz.  In this case, the coil
> is shielding the topload sphere, rather than the other way around.


I will try some top terminals out to see what works well.



>
> The energy storage capacitance of the secondary (with sphere) is
> around 27 pF, so if you had say a 9kV primary voltage, the peak top
> volts could be up to
>
>    Vpri * sqrt( Cpri/Cee) = 9kV * sqrt( 55nF/27pF)
>
> which comes out at around 400kV.  That gives an average radial
> field of 400kV/22 kV/inch = 18 kV/inch.  Remembering that 80% of
> the voltage is impressed across the outer 50% of the winding, the
> actual value would be nearer 30kV/inch.  Added to this would be the
> additional induction from the primary, and the tssp model reports a
> worst case radial gradient of 2kV/turn, or 29kV/inch at 11% in from
> the rim.  I don't know whether that's enough to cause racing arcs.
>

In actual fact im running on a crap DC system at the moment so the overall
output will be a lot less. I will convert back to AC to compair it correctly
with a tube wound coil. But for now it will proably only arc a few inches,
better for testing out new stuff aswell :)


> Can't give more accurate predictions without knowing how the coil is
> supported, but I hope these figures help to give some sort of feel
> for the territory you are entering.


Flat coil ?  At the moment its just on a wood circle on the floor, I will
probably rasie it up off the floor a few inches in actual use. I will also
have to do the same for the primary. I am not sure about a large primary
support yet so I may have to build it in 4 sections and fix them together.
I 4foot circles will be of course very big, bigger than the wood I can fit
in my car!  It all looks as if its comming together. Still varnishing ATM, a
few days I can take more values from it. I think you have them pretty much
on track anyway...

Chris




> --
> Paul Nicholson
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