Cap break down voltages

           Cap break down voltages
           Thu, 03 Apr 1997 15:02:20 -0500
           Julian Green <julian-at-glosilk.demon.co.uk>

I am about to start capacitor building again and want to know a good
working voltage to choose.   I currently have
3 home made poly/foil caps 0.03uF -at-10KV.   These caps have
40mils of good quality poly between the plates.

Some time ago I remember Richard Hull posting about chemical breakdown
of the dielectric where voltages exceed 10KV.   

If this is the case then I see little point adding to the thickness of
the poly for a higher voltage rating.   I will simply build more of my
0.03uF 10KV caps and wire them in series.

I would also like to ask about primary operating voltages.   Currently I
am using a 11KV pole transformer with no balast, just RF chokes in the
primary circuit.   When I fire the coil up I make sure my rotary gap is
running at full speed before applying the power via a variac.

As far as I can tell the current drawn by the pole transformer is low
(no AC amp meter fitted yet).  The coil runns very smoothly generating
no more than 36" arcs.  Heating of the rotary electrodes is also low. 
The coil has no toroid to speak of being a 12" on a 10" coil.  New
toroid in under construction.

To get more arc should I:
1)  Add more primary capacitance and use fewer turns on the primary
(currently tapped at 10 turns using 0.03uF)
2)  Up the primary input voltage by adding a second pig. This will also
mean wiring caps in series and using more turns on the primary.
3)  Add balast and PFC

Coil spec is 1000 turns on 10" x 36" secondary.  11 turns
primary with 3/8" pipe.

Comments welcome

Julian Green