IMO, the issue of reforming is very much alive with electrolytics, old and new.
In some modern PZT actuator drivers, there is a warning to bring up the supplies slowly if the unit has been dormant for sx months or more. -John ================ > Oh to add further information. > I love old caps. They go bad and I get my test equipment for cheap. > That said I do measure the caps I am going to put in on a old style HP cap > meter that can apply up to 100 volts to the cap. I look for leakage. What > I > see in quite modern caps that have been around for a while (Surplus you > get > at hamfest approx 3-5 years) is that there is a higher leakage current > that > does settle down after a while. So I sense the forming effect still > exists. > Am I wrong about this?? > Regard > Paul > WB8TSL > > On Wed, Jun 22, 2011 at 1:16 AM, Chuck Harris <[email protected]> wrote: > >> Hi Bill, >> >> I agree with your forming information, as applied to older caps, >> but not your temperature information. The 105C high temp caps >> are just as happy, or unhappy really, with low temperatures as >> the 85C caps. Basically the difference between the two is water. >> The 85C caps have an electrolyte with a significant amount of water, >> that boils dry at high temperatures. The 105C caps don't. Kind >> of like the difference between an antifreeze and water solution, >> and straight antifreeze. Both seriously run out of capacitance >> when they get below freezing. >> >> The loss of capacitance can really bite you when you use integrated >> low overhead voltage regulators in automotive temperature ranges. >> The regulators will oscillate if they don't have enough capacitance >> on their input terminals... which can happen if you specify an >> electrolytic capacitor that is right around the 100uf needed. When >> it gets to 0C, and becomes a 10uf capacitor, the regulator takes off >> and burns up your load. >> >> -Chuck Harris >> >> >> >> Bill Hawkins wrote: >> >>> Group, >>> >>> During my days of interest in antique radios, I learned that >>> the dielectric between aluminum plates was formed by passing >>> current in one direction to build up an oxide coating on the >>> plates, which became the dielectric. The thickness is directly >>> proportional to working voltage and inversely proportional to >>> capacitance. As we learned from reforming old caps, the oxide >>> thins when there is no voltage on the cap, but can be restored >>> by passing several milliamps through the cap. Applying rated >>> voltage before it was formed would destroy the cap by welding >>> spots of the plates together. >>> >>> I'm not sure that this applies to modern caps. >>> >>> As to the temperature rating, a high temp cap run in a cool >>> environment will be as unhappy as someone transplanted from >>> Miami to Minneapolis in the winter. It may work, but it will >>> be very unhappy - so it depends on your empathy for the cap. >>> >>> There ought to be a way to work precision time into this >>> thread, but I can't think of one. >>> >>> Bill Hawkins >>> >>> >>> -----Original Message----- >>> From: Poul-Henning Kamp >>> Sent: Tuesday, June 21, 2011 2:40 PM >>> >>> In message<4E008A73.50701@erols.**com <[email protected]>>, >>> Chuck >>> Harris writes: >>> >>> and yet, I find that some electrolytic >>>> capacitors that have been run at lower than normal voltage improve >>>> markedly >>>> when "reformed" by applying rated voltage through a 10K resistor for >>>> a >>>> couple of hours. >>>> >>> >>> I noticed in a datasheet at one point, that the capacity only was >>> warranted above a certain percentage of rated voltage. No explanation >>> was given. >>> >>> >>> >>> ______________________________**_________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to https://www.febo.com/cgi-bin/** >>> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >>> and follow the instructions there. >>> >>> >> ______________________________**_________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/** >> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
