Re: bulk buy of super caps?

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

Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>" <presence-at-churchofinformationwarfare-dot-org>

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, September 11, 2001 8:08 PM
Subject: Re: bulk buy of super caps?


> 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

Mylar as in the typical ebay "tesla coil" capacitor.

> not ideal (they are very sensistive to
> overvoltage), followed by plastic capacitors, of which polypropylene is
the

If you know what voltages you are dealing with to being with, overvoltage is
not an issue. My outlet should supply 120 volts. I don't use appliances that
self destruct at 121 volts. Important things like traffic light bulbs are
sometimes rated at 130 volts.

> 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

Risetime is also dependant on the dielectric itself. This is why some
ceramics are too "slow" and are poor for Tesla Coil use and some seem to
work ok. The wiring in both cases is a metallized face on each side of the
disk. As in magnetics, dielectrics have hysteresis. This is why a cap can
shock you after you'd discharged it.

> comes into it.  :)  Again, rise time does not effect the amount of power a
> capacitor can discharge, but how fast it can

This is incorrect. Power is energy/time. If you cannot get the energy out of
a cap quickly, the power you draw from it will be lower than if you can get
it out faster. The total energy content (Joules) is the same for any voltage
and capacitance.

> 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,

If the power never gets to the spark gap, it does not matter what the spark
gap does with what it does get.

> where most of the losses occur.
>            --mike

KEN