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.
