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I obtained some supercaps from an auction site.
As is often the case for low cost components from such sources, these do not have supplied data and such branding as there is does not appear traceable.

I would like to know if there is a standard for polarity for such devices and how likely it is that generic devices such as this one follow the "standard".
My samples have an arrow on the label which may indicate polarity, but this is uncertain.

To make my query specific, but also liable to be generally useful, here is a set of closely related questions:

  • What is the polarity of this supercapacitor (4F, 5.5V)?

  • How was the polarity determined in this case?

  • Is there a standard for polarity for such capacitors?

  • What does the arrow indicates?

image of two-cell stacked coin-like supercapacitor

Some details of specific product here

Including this diagram:

enter image description here

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  • \$\begingroup\$ You have a great answer. Accept it. The lead on top in your picture is (-) and the lead we can barely see, on the bottom, is (+). \$\endgroup\$ – jonk Aug 13 '16 at 18:47
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    \$\begingroup\$ Their dimension description drawing contains the polarity \$\endgroup\$ – PlasmaHH Aug 13 '16 at 19:48
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    \$\begingroup\$ You should post this question to the eBay seller. EE.SE isn't his volunteer technical support. \$\endgroup\$ – Nick Alexeev Aug 13 '16 at 19:53
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    \$\begingroup\$ @SolarWind I added a coy of the relevant product link which had been inappropriately deleted and the dimension image as I cannot post an answer. On the dimensioning image you can see very small polarity sumbols next to the leabs - "-" by the B text and "+" to the left of the P text. \$\endgroup\$ – Russell McMahon Aug 13 '16 at 21:36
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    \$\begingroup\$ @SolarWind I edited your question so that it becomes more generically useful. The aim was to make the question of long term value for people seeking to design equipment using generic components readily available on auction sites. Hopefully the rewritten question is consistent with your original intentions but looks less like a 'shopping question'. Feel free to re-edit as appropriate (Hey, it's your question :-) ). I've asked the moderators to reopen the question. \$\endgroup\$ – Russell McMahon Aug 14 '16 at 14:46
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Since the product you purchased has no background information, you can't be certain. However, the convention for these stacked-disk type capacitors is polarity mark points to negative lead. This is the same as is the convention with conventional electrolytic capacitors.

For example, the Eaton KR-5R5V474-R:

Digkey image of the KR-5R5V474-R

Has its datasheet show:

device drawing of the KR-5R5V474-R showing polarity indication

Similarly, for the Panasonic EEC-S0HD224H:

Digikey image of the EEC-S0HD224H

Has the same arrow convention considering the asymmetric leads with polarity indicated in its datasheet:

device drawing of the EEC-S0HD224H showing polarity indication

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    \$\begingroup\$ I suppose that makes sense by analogy with CR2032 (etc.) cells where the smaller-diameter electrode is negative. But why do capacitor manufacturers make the labelling so cryptic? (Rhetorical.) \$\endgroup\$ – Andrew Morton Aug 13 '16 at 18:54
  • \$\begingroup\$ Why do capacitor manufacturers make the labeling so cryptic? (Actual non-rhetorical question) :) \$\endgroup\$ – WeGoToMars May 6 at 9:49

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