> On Fri, Apr 8, 2011 at 10:20 AM, Andre Abelian > wrote: >> Hi all, >> >> mistakenly I used super cap reverse polarity so + pin is connected to >> ground and >> - pin goes to >> RTCC chip. when I checked cap was charged and every things working fine >> hardware >> wise. >> this mean super cap is charged wrong polarity without knowing but as far >> as >> functionality it works fine. >> looking inside electrolytic cap it is only a pair of foil wrapped >> together. my >> question is this >> how does + pin define? or how do they figure out + and - pin? >> based on my testing electrolytic cap do not have polarity. >> >> any idea how + pin is defined? >> >> AA >> > > http://en.wikipedia.org/wiki/Electrolytic_capacitor > > Hint: it's not the foil, it's the electrolyte. > > Regards, > Mark > markrages@gmail >From Wikipedia: It was not until World War II, when sufficient resources were finally applied to finding the causes of electrolytic capacitor unreliability, that they started to become as reliable as they are today. A major advance was the process of etching and pre-anodizing the foil prior to assembly, which allowed the use of much less corrosive electrolyte solutions, which in turn meant the devices could be left unenergized for long periods without deterioration. Modern electrolytic capacitors can remain usable after lying idle for decades, whereas the original Mershons could not tolerate more than a few months without a polarizing voltage. Elaborate "re-forming" procedures were necessary to avoid damage to receivers that had not been used for some time. I remember the idea of "re-forming" electrolytics. I was under the impression that this process was done originally to polarize the capacitor. But, it appears the two pieces of aluminum foil may be different, as one appears to be "pre-anodized" in the discussion above. In my thinking, the large capacitance to volume ratio of electrolytics is due to the large plate area due to etching of the foil, creating a large surface area, and due to the extremely thin dielectric (oxide on the aluminum). I think non-polar electrolytics treat both pieces of foil the same so there's oxide on both plates. The electrolyte then becomes one plate of each of two series capacitors, one being one foil and electrolyte, the other being the other foil and electrolyte for the plates. Since this is two capacitors in series, you only get half the capacitance. Super-caps are a bit different... See http://en.wikipedia.org/wiki/Super_capacitor . Harold --=20 FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available! --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .