Re: Capacitive Transformer "maxed out"?

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Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

 > Original poster: "Jolyon Vater Cox by way of Terry Fritz 
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

 > The longest spark I have drawn from it is about 1 inch to a pointed
 > terminal when a 3 3/8" disc is used as the topload.
 >
 > I have allowed a hole diameter of 2 1/4" between the influence ring and L2
 > and have wrapped a length of 15/1000" thick plastic sheet inside this hole
 > to act as a spark preventer; I still get corona around the inner edge of
 > the ring however. Would widening the hole be beneficial or detrimental to
 > performance?

A wider hole will avoid the corona problem, and will allow the voltage
profile at the secondary to reach a higher voltage at the top. To
experiment without having to modify much the current setup, use a
simple loop of insulated solid wire as the influence ring. Allow
some overlap, so you can experiment with different diameters.

For the size and clearings in your setup, I would not expect much
more than 1" sparks.

 > I have tried much bigger caps (salt-water caps made from pop-bottles of
 > 300ml upwards as well as 250ml food containers) these gave very poor
 > performance even when the topload was made larger to compensate. Does this
 > mean that my design has reached the limit of what is possible?

Tuning is critical, and the only way to tune this system with fixed
inductors is to change the capacitances. Try a small telescopic antenna
as top load. It's not the best for long sparks, but turns easy to
see if the system is in tune.

 > I have another former 4 3/4" tall and 2 1/8 in diameter. Suppose I wound
 > this with 40SWG to a length of 4 1/4" I would have 803.25 turns and
 > 13990.535 uH.
 >
 > If I kept k and l ratio of 9:10 and designed a new L1 accordingly would I
 > likely get longer sparks than at present?

The mode 9:10 was for the directly coupled system. With the same
components the mode goes to something around 19:20 in the capacitive
transformer version (double the higher multiplier).
The mode fixes the maximum voltage gain (~sqrt(L2/L1)). If the primary
capacitor is the same, the power will be the same too, and the output
will not change. For greater output you have to use a higher mode, but
then losses increase and tuning becomes more critical. My best system
of this kind so far operated in mode 41:42.
You mention that your capacitors use a solid paste as internal
conductor.
I would expect this to result in lossy capacitors. Have you tried
metal foil glued to the inner sides of the capacitors? This is the
best solution for low losses.

Antonio Carlos M. de Queiroz