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I bought six supercapacitors and connected them in series to get a total voltage of 16.2 VDC.

The product's Mouser No is: 723-BCAP0450P270S18, Mfr. No is: BCAP0450 P270 S18, the datasheet can be found on this link:

The problem is that I applied reversed voltage to charge the supercapacitor bank. The supercapacitors were charged (starting with 10A charging current) until reaching their optimal voltage (2.7 VDC each) and the day after, I discharged them using resistors. This happened three to four times. They do not seem to have suffered any damage and no problem occurred during this procedure, so I would like to ask:

  1. Might the supercapacitors have been internally damaged and they are dangerous to use?
  2. If not, should I keep charging them using reversed polarity or should I apply the correct polarity to charge them again.
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    \$\begingroup\$ The Wikipedia article on supercapacitors says that reversing the polarity will reduce the capacity. You might want to measure the stored charge using the correct polarity to see if any damage has occurred. \$\endgroup\$ May 9 at 18:58

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Electrolytic capacitor polarization is initially set at the factory by applying voltage to form the insulating oxide layer.

That is why caps have a polarity and these standard supercaps are no different. Reversing the polarity will damage the original insulating layer first and then start to form a new insulating layer with the applied polarity. It is not something that should be allowed to happen, so consider the capacitors damaged, or at least degraded, and they could be unstable and dangerous too.

Here is also what manufacturer says about reversing the polarity:

https://maxwell.com/wp-content/uploads/2021/08/Notes_on_Using_Ultracapacitor_Cells.pdf

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  • \$\begingroup\$ glynstore.com/content/docs/maxwell/… see p35. This contradicts the information you offered \$\endgroup\$ May 10 at 8:12
  • \$\begingroup\$ @TonyStewartEE75 OK, page 36 says the PC series will also degrade but to a lesser degree. So it should be considered just degraded, not damaged. \$\endgroup\$
    – Justme
    May 10 at 8:32
  • \$\begingroup\$ Does this mean using them with the correct polarity can re-form the insulating layer? \$\endgroup\$
    – user253751
    May 10 at 10:52
  • \$\begingroup\$ I agree the main thing is this explains why it did not self destruct like normal polar caps, and some degradation is expected \$\endgroup\$ May 10 at 12:05
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Additionally to the note found in the document linked in Justme's answer:

All ultracapacitors have a positive and negative polarity. Please check the polarity indicated on the label before use and do not reverse the polarity when electrically connecting the ultracapacitor cells

There is also this one in their document about modules:

Applying reverse voltage on ultracapacitor module(s) may result in malfunctioning, rapid performance degradation, and/or catastrophic failure of the module. The polarity of the module terminals must be checked in advance for the correct connection of the power lines.

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I wonder if these are non-polarized since both electrodes in this part number are carbon. If you see no ill-effects, that may confirm this but the double-layer-effect may be more advantageous in one polarity.

Looking now at the specs, I see they are non-polarized and Vr reverse voltage defines the voltage limit . (

(Although the R in \$V_R\$ is defined by Maxwell as Rated not Reverse)

VR Rated Voltage – – 2.7 V

VSURGE Surge Voltage Note 1 1. Surge Voltage Absolute maximum voltage, non-repetitive. The duration must not exceed 1 second. – – 2.85

Additional Information

Polarity / Reverse voltage

Unlike many batteries the anode and cathode of an ultracapacitor are comprised of the same material. If the positive and negative terminal and casing are also comprised of similar materials, then theoretically the ultracapacitor has no true polarity.

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Putting electrolytic capacitors with reverse polarity will almost certainly with prolonged use cause them to explode and the fluids of the electrolyte will come out which is dangerous.

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  • \$\begingroup\$ My point is it isnt safe to use electrolytic capacitors with reverse polarity. \$\endgroup\$
    – Jun Seo-He
    May 10 at 8:15

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