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I have an NIC aluminum electrylytic capacitor and am trying to figure out which wire is positive and which is negative. Forgive me if this is a stupid question since I'm a total noob at this.

This is what's on the datasheet (Source: NIC Components)

The actual cap has the same polarity marking (a rectangle) on its casing. Does it mean that the wire with the marking is negative and that the other one is positive?

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  • \$\begingroup\$ Got it. Thx to all. \$\endgroup\$ – bubbles Aug 27 '13 at 0:15
  • \$\begingroup\$ I thought this was going to be "How to tell if the leads are the same length and the markings are missing..." \$\endgroup\$ – JYelton Aug 27 '13 at 1:48
  • \$\begingroup\$ Wait until you use your first SMD tantalum cap :) \$\endgroup\$ – Szymon Bęczkowski Aug 27 '13 at 6:55
  • \$\begingroup\$ @JYelton, I thought the same thing and wanted to know the answer. I asked another question on the subject. Will appreciate if you share your knowledge: electronics.stackexchange.com/questions/80327/… \$\endgroup\$ – Vasiliy Aug 27 '13 at 11:52
  • \$\begingroup\$ @Szymon I use SMD tantalums on a few projects. The ones I use are marked with a stripe on the positive terminal. \$\endgroup\$ – JYelton Aug 27 '13 at 15:52
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Generally (not always, due to manufacturing defects) the short lead is the cathode, negative; while the long lead is the anode, positive. When looking at the can, the lead that matches up with the rectangles which are negative signs, is the cathode side.

On SMD aluminum cap cans, the topside marking usually denotes cathode as well. SMD tantalum caps, the line usually marks the anode side.

The absolute best way to tell, is to look at the datasheet and see how they call it out, though the above can be used as a guideline.

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The "rectangle" is actually a minus sign; this marking indicates the negative lead.

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Yes. You don't believe the manufacturer's datasheet?

Normally, the negative terminal of and aluminum electrolytic capacitor is "marked". The "rectangles" shown on the datasheet can be considered as minus signs.

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