Hi Well …. ummm …. errr …. it turns out that there *are* (or were) papers published on the topic that are “well known” in the … errrr …. space community and pop right out of the stack of papers that the guys from …. errr …. a well known space outfit in California bring with them ….
The issue is that below some magic percentage of the rated voltage, the dielectric may try to re-form. When it does, the outcome is a bit unpredictable. As I recall it applies both to tantalum and aluminum parts. There are different factors for the two types. Keep in mind this all came up in a meeting in the mid 1990’s ….memory is only just so good ... Bob > On Feb 25, 2019, at 9:56 AM, jimlux <jim...@earthlink.net> wrote: > > On 2/25/19 5:48 AM, Bob kb8tq wrote: >> Hi >> Indeed there is both a minimum and a maximum working voltage for a properly >> derated electrolytic >> capacitor. We found that out in the middle of a design review when the >> customer’s team brought it >> up … (much to our surprise). >> Bob > > > The Cornell Dubilier app guide doesn't seem to mention it. > http://www.cde.com/resources/catalogs/AEappGUIDE.pdf > > NAVSEA derating guidelines make no mention of it: > https://www.navsea.navy.mil/Portals/103/Documents/NSWC_Crane/SD-18/PDFs/Products/Capacitors/CapacitorsDeratingRevB.pdf > > They're both appear to be focused on essentially setting a lower voltage as a > thermal consideration, and not on a "giving you more margin to failure > voltage". > > https://www.illinoiscapacitor.com/pdf/Papers/reliability_of_capacitors_general.pdf > > says you only get a max of twice rated life by derating. Maybe that's > because of the "reforming of the dielectric to a thinner layer".. > > This is a compendium from 1981 of all sorts of capacitor information but > doesn't seem to address derating. > https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810017835.pdf > > > https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160003309.pdf has a > lot of info on wet slug tantalums.. > > > > >>> On Feb 25, 2019, at 1:48 AM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: >>> >>> -------- >>> In message >>> <CADHrwpcdmyeguXoM69D2byW=DfKwMfi7_t-P=qYst7T7OO=e...@mail.gmail.com>, Dana >>> Whitlow writes: >>> >>>> This would seem to imply that purposely overrating a 'lyt is pretty >>>> pointless. >>>> >>>> Any comments on this notion? >>> >>> I've always wondered that myself, and found very little documentation or >>> wisdom available. >>> >>> As I understand it, even very brief voltage spikes must be kept under the >>> rated voltage, so overrating would buy some transient durability, but >>> other than that... >>> >>> -- >>> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >>> p...@freebsd.org | TCP/IP since RFC 956 >>> FreeBSD committer | BSD since 4.3-tahoe >>> Never attribute to malice what can adequately be explained by incompetence. >>> >>> _______________________________________________ >>> 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. > > > _______________________________________________ > 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.
