In Reply to: Sorry, no bangs on reversing 'lytic cap to DC. (long) posted by cheap-Jack on February 26, 2007 at 12:44:05:
If your battery voltage dropped, you simply didn't have enough energy to cause the cap to fail in a dramatic way. You need a lower source impedance. Try a car battery and a backwards tantalum cap. Wear oven mits :)I've personally had the pleasure of having molten tantalum melt it's way through my shirt; strangely, somtimes the cap doesn't explode and catch fire, but rather shoots moltem metal at you. Also have had the pleasure of containg a fire in a burn-in oven caused by backwards Ta caps. Not to mention many PCB's with a lump of charcoal with leads on it that smell bad. Trust me, they will catch fire if there is enough energy available to heat them up.
Oh, BTW, some modern Ta caps have a current limiting fuse in series so that they just open up instead of blowing up. Darn UL ruins all the fun...
My experiences with Aluminum caps aren't as dramatic. Put 450-500V across a 300V snap-in electrolytic and it gets hot, then pops the seam on the top, spewing hot goo. I've heard that they too can explode but haven't had this happen to me.
I think many Al caps will exist just fine with reverse voltage to a point. Past some voltage they will start leaking current and heating up. Also I believe that the dielectric breaks down over time, so even though it may be happy for a few hours, eventually the dielectric will break down (dissolve) and the cap will short.
Pete
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Follow Ups
- Try a car battery. - Pete Millett 00:22:10 02/28/07 (8)
- Thanks yr concern to an "idiot" like me. - cheap-Jack 08:11:45 02/28/07 (7)
- Re: Speaking of such - Ron Oehlert 09:28:01 02/28/07 (6)
- So where to post you think would be more appropriate ? - cheap-Jack 10:51:25 02/28/07 (5)
- should "tube diy" readers start discussing cables/speaker/etc in this forum section because they are capable? - jarthel 21:57:15 02/28/07 (1)
- No, strictly speaking, they should not. - cheap-Jack 07:41:33 03/01/07 (0)
- all these irrelevant stirrup - Russ57 13:50:56 02/28/07 (2)
- How "much better" today's cap performance ? - cheap-Jack 12:57:38 03/01/07 (0)
- Let me clarify ... (very long) - cheap-Jack 08:42:39 03/01/07 (0)