Hi guys, yes, Electrolytics, the OS-CON are specified at an internal +20C temperature rise when running at rated AC current, and that's probably when they are brand-new and have all of their initial capacitance. Temperature rise in high current apps will probably increase as the part ages and looses capacitance. Electronics in an enclosure can easily run at +30C above ambient due to self heating, so +50C to ambient on the capacitor can easily happen. With a 30C ambient, we are looking at 80C on the cap, and are down to a year lifetime again on the standard OS-con caps (they seem to have long-lifetime special models available too which are probably much more expensive). Let's keep in mind that the OS-Con caps standard lifetime versions are already very expensive in my opinion.
Also, Sanyo specifies "lifetime" not MTBF! Assuming this means useful lifetime with less than 50% decrease in capacity, this may mean that the MTBF is actually much lower than that, since many designs may not work properly with -50% capacitance, or have more than +20C self heating on the cap. We have to remember that it may work on a particular installation for years on end especially if it used as a DC bypass cap without any AC current on it, but when designing products we cannot rely on anecdotal information, but rather have to do the math based on the parts' specsheet and the products expected worst-case ambient environment. In my opinion: Use foil caps to avoid vibration-microphonics. Very expensive, but hey you get what you pay for. Use Tantalum caps if bulk bypassing is needed, using multiple 100uF units if necessary. The design is not right if you need more than say 470uF anyways unless you are switching tens of amps as in an Audio power amp.. Use ceramic caps where vibration is not an issue. Use high frequency (>2MHz) switchers wherever efficiency is required, otherwise use linear regulators. Use electrolytics ONLY in external disposable low-cost power supplies, such as the $15, 12V 1A Wall Wart supplies available at Mouser etc. Just my own opinions.. bye, Said In a message dated 11/27/2011 23:22:08 Pacific Standard Time, [email protected] writes: On Fri, 25 Nov 2011 22:25:37 -0800 Chris Albertson <[email protected]> wrote: > One question: How does one avoid using electrolytic caps if you need > (say) 1,000uF or even 100uF. Those would be some mighty big film > caps. I think, aluminium electrolytics are meant, as these have a lot of "wear" and can die. Hence, you can use tantal or niob electrolytics, which have a dry eletrolyt. Or you can use ceramics which are already available at 100uF. Attila Kinali _______________________________________________ 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.
