Re: bulk buy of super caps?

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

Original poster: "Michael H Nolley by way of Terry Fritz <twftesla-at-qwest-dot-net>" <nolleym-at-willamette.edu>

> Can you support this with some facts or numbers? Why are lower class ceramic
> caps awful for tesla coil use? Could it is about risetime and ESR?

    I don't have the numbers unfortunately--would someone who is familiar
with one or the other of those spec sheets
post them?
    As to the ceramic caps, they are awful because of the dielectric
performance.  generally speaking, the less
physically flexible the dielectric is, the more lossy it is in RF circuits.
 Lossy caps tend to heat up as the
frequency increases. I don't know the exact physics of this.  All I know is
that ceramics are the worst, followed by
mylar caps, which are also bad, mica caps which are quite good, but still
not ideal (they are very sensistive to
overvoltage), followed by plastic capacitors, of which polypropylene is the
most preferred.  LDPE and HDPE are also
quite serviceable as dielectrics.  Rise time doesn't have as much to do
with dielectrics (someone correct me if I am
wrong) as plate design, placement, and the resistance of all of the
component wiring.  This is where copper ribbon
comes into it.  :)  Again, rise time does not effect the amount of power a
capacitor can discharge, but how fast it can
do it, and thus the instantaneous power available.  Since the Tesla coil
relies on fast primary to secondary current
transfers, fast rise time is desirable, but has much less of an effect on
performance than, say, spark gap design,
where most of the losses occur.
           --mike