>
>
>Rich, AG6K, writes:
>
>>The ESR of flash-caps appears to be higher due to use of thinner plate
>>material - which allows the designer to pack in more C - and more Joules
>>per unit of volume.
>
>This is of great interest, Rich. Let us suppose that the plates
>are ultra thin, but that the insulation is of the standard dimension.
ok, except that the insulation in flash capacitors appears to be operated
somewhat closer to the actual breakdown potential, according to failure
comparisons with a high-pot. tester .
>If that be true, *voltage* ceases to be the issue. Instead,
>*current* becomes the problem.
agreed
>Does it make any sense to imagine
>the following?
>
> Thin plate material is OK in flash service, even to handle
> the huge (but only occasional) current flow in a discharge,
> because the slow rate of recharge requires tiny current flow,
> and there is a long static interval between discharges. Thus,
> there is no tendency to overheat.
yes
> In filter-cap service, though, the cap is charged and
> discharged (albeit only incrementally) all the time,
> so some current ingress and egress goes on constantly.
> Might this create a heat accumulation problem that would
> be absent in flash service?
Yes. *Average* ripple current is likely to be minimal in flash service,
and maximal in broadcasting service. Making the plates thicker reduces
heat by reducing ESR, which increases volume per joule.
Capacitor engineering is a balancing act. Where practical, in order to
store more joules per cubic centimeter, one uses thinner plates and
thinner dielectric.
Rich...
R. L. Measures, 805-386-3734, AG6K
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