In response to my query about derating of flash-discharge
capacitors, I received insightful and valuable comments
from each of Marv (W6FR), Rich (AG6K), Ian (G3SEK), and
Len Schaier. I thank you, one and all.
Given that half of the responses came from W6's, are we
seeing empirical support for the time-worn assumption some
people make about "California Kilowatts"? Just kidding, guys.
Now I have a sordid confession to make. I still toy with
power supplies that feature resonant-choke-input filters.
Nearly everyone else at the ham level uses capacitor-input
filters, at least for HV supplies, for reasons of which I am
sure most of us are aware.
Moreover, isn't Henry Radio the last holdout, among manufacturers
of amps. for the ham market, to use a resonant-choke-input filter
in any of its units? Other than Henry amps., the last "ham" product
that comes to mind as having that sort of filter was the Collins
30S-1. As to that, it is perhaps a stretch to regard the 30S-1 as
being targeted to the amateur market, given the number of those that
were sold to MARS, the U.S. Department of State, and the like.
Enough rambling. I have a follow up question about flash-
discharge caps.
The consensus seems to be that average ripple current is the thing
that impairs the longevity of flash-discharge caps. when they are
subjected to DC filter applications. The thinking is that the
voltage breakdown is the long-term result of heat rather than
excess potential. The wisdom behind the 50% or 60% derating
figure is that the reduced ripple-current throughput that is apt
to occur at the lower potential is easier on the cap.
FB, I love it.
Does it follow from all of this that a resonant-choke-input filter
requires less derating of a flash cap than does a capacitor-input filter?
With the latter class of filters, the cap is asked to do the "heavy
lifting" with respect to smoothing of ripple. With the former
class of filters, the resonant-choke circuit takes the brunt. Is
it reasonable to assume that a flash-discharge cap will survive
longer, and be safe with less derating, when it follows a
resonant filter?
Thanks again, fellas.
73 de Bob, K0KR
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