Actually the leakage of at least some standard electrolytic capacitors can be quite low if one waits long enough. I've seen a leakage as small as a few nanoamps after several minutes at room temperature with randomly selected 100uF capacitors.
Bruce > On 30 August 2019 at 18:53 ed breya <e...@telight.com> wrote: > > > I think there may be some confusion over the "super-capacitor" term. > Over the years, I've seen two types. > > The most commonly encountered are the ones in consumer gear, for storing > charge to keep CMOS RAM alive during power outage and such, for a > reasonable amount of time. These may be from 47 mF to a Farad or so, and > have high ESR - they're not expected to dump huge charges, rather steady > uA range flows for the CMOS. > > The other, more exotic kind are for bigger energy storage and power > conversion - these have very low ESR, like batteries, and may have lots > of Farads, but generally low working voltages, similar to a battery > cell. Higher working voltages are attained by stacking, with the > expected reduction of capacitance, of course. > > I've only played with the former, since the latter were unusual and > expensive. One thing I can say is that the CMOS backup types are pretty > crappy capacitors for any use beyond their normal role, and they don't > last very long, in terms of service life - perhaps a decade or so. Most > that I've salvaged were found to be nearly totally open, like regular > old electrolytics after their juices have evaporated. > > There may be more types nowadays, that overlap a number of applications. > > In the situation I mentioned previously, I was planning on paralleling a > bunch of references to average out the noise somewhat, with combining > resistances around a hundred ohms. I had hoped to put a bunch of big > OSCONs in for filtering at the summing junction, but was wary of their > possible leakage currents lugging it down. I figured I could use > reasonable-valued, low leakage Ta caps instead, with enough low noise > amplifier gain to boost their effective values. > > Ed > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
