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Re: Fw: Fair Radio Sales HV capacitor
Tesla List wrote:
>
> Now it is interesting that you didn't see any performance difference
> between your rolled PP/oil and this cap! Is it possible that there were
> other significant system losses that masked the loss from the commercial
> cap? For example, could your home-brew cap have had substantial internal
> corona losses? The latter may be why the homebrew unit subsequently
> failed.
If you are running several kW into the coil, and dissipating only 1% in
the cap (which would be a small fraction of the total power), you are
still dissipating a few tens of watts. I venture to say that you
wouldn't touch a 40W lightbulb after it had been on a few minutes.
I suspect that cap losses, unless they got really high, are going to be
a small fraction of the ohmic and other losses in the system. Sort of
like arguing about whether PVC or cardboard has a higher loss tangent
for a coil form, and whether it makes any real difference. For instance,
a 50 uH copper primary at 100 kHz (for example) has an AC impedance of
about 30 ohms, and a loss resistance of around .05 ohms. Compare this
ratio (.0016) to the loss factor quoted for mylar (.005). Sure, the loss
due to the cap is 5-10 times that for resistive losses in the primary,
however, in either case, the loss is less than a percent. All that
energy is going somewhere else.... (Spark gap heating, ionizing air,
heating the secondary, etc.)
--
Jim Lux Jet Propulsion Laboratory
ofc: 818/354-2075 114-B16 Mail Stop 161-213
lab: 818/354-2954 161-110 4800 Oak Grove Drive
fax: 818/393-6875 Pasadena CA 91109