red capacitors


I'm not sure but they sound like ceramics to me. They probably would be
too lossy and heat up too much in Tesla use. The capacitance is also
fairly low. They may possibly be mica, in which case the current
handling would be too poor. Always always go for polypropylene
dielectric and you won't be faced with any of these problems.
Preferably the foil types but metallised types like mine are OK as long
as the connections are foil rather than film. If you look at the data
for any of the caps the big thing to look for is the dV/dt rating,
which determines the max current allowed. Although in most cases this
can be exceeded by a small factor for low duty cycle use, you should
be looking for a figure of no less than 1000V/us. Work out the primary
current (see other recent posts on efficency, cap size & bps for this)
and then see what you total imaginary cap array would take, ie

Max amps (rated) = Total capacitance * dV/dt

You will probably want a cap array that has a rated current of around
200 (absolute minimum I'd say) to 1000A. I would reccomend types from
Wima, Evox Rifa and Phillips (the last look very sturdy but the range
is somewhat small for the 'top flight' (dv/dt > 10,000V/us) 376 series)

Go straight to the mfr, ask for a good distributor in your area and you
may get a better deal than the 'high street' electronics stores. They
will also send you their entire data library for free!

Mine are Evox Rifa PHE428 series, dV/dt 1300V/us at max DC rating,
2500VDC 0.047u types. 10 strings of 7 in series. No problems so far -
they remain stone cold although without any bleed resistors they seem
to present a significant shock hazard (I got bitten once, never again!)

Best of luck finding what you need...

Alex Crow

On Sun, 13 Jun 1999 05:10:25 Tesla List wrote:
> Original Poster: "Kevin Wahila" <knw2-at-lehigh.edu> 
> I have a box of red, 2500pF, 15kV, 1" diameter capacitors.they are of the
> type D70X5R25M15KV and the T.C. is X5R.  well that doesn't mean a whole lot
> to me, i am not familiar with them, but maybe someone on the list is.
> would the voltage rating on them be a DC rating?  if they are DC and i
> wanted to employ them in my coil would parallel strings of 3 in series be
> suitable to take care of and AC supply voltage of 9kV?
> thanks
> kevin wahila