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I have multiple metal case capacitors that I need to cool. The thermal tape I use is conductive (carbon based). Also larger heatsink on the left might touch capacitors on the left side. The question is, is it safe to do so? I assume that yes, because capacitors' metal cases should be isolated from the rest of it (only pins is actually connected, right?) - but I'm not 100% sure.

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    \$\begingroup\$ Add a link to the datasheet into your question. \$\endgroup\$
    – Transistor
    Commented Jan 11, 2022 at 18:00

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I have no direct answer, but it's rather easy to test: take a multi-meter (in continuity tester mode, or if it don't have it in resistor mode,) and check if there is a connecton between metal and each of the pins.

If you don't have a multimeter, you can even do it with a battery and a LED+resistor or another small lamp. Just be careful not to apply reverse polarity on the capacitor (ie to test if negative pin is connected to case, connect negative pin to battery minus and put the LED and resistor between case and battery + ; to test if positive pin is connected to case, connect the positive pin to battery +, and put LED+resistor between case and battery -.

Be careful not to use a battery voltage greater than the capacitor rating (2.5V for the ones on the left if I read right.)

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  • \$\begingroup\$ I checked with the multimeter and neither 2V or 16V caps' legs have any connection to the case. In fact, the case itself is non-conductive somehow! IDK it certainly looks and feels metal, but maybe it has some enamel coating. Even at 20MOhm setting was nothing. \$\endgroup\$
    – ScienceDiscoverer
    Commented Jan 11, 2022 at 18:26
  • \$\begingroup\$ There is a direct answer, and it is not rather easy to test. \$\endgroup\$
    – Justme
    Commented Jan 11, 2022 at 18:26
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    \$\begingroup\$ @ScienceDiscoverer The can is made of aluminium. It is a metal which forms an insulating oxide layer, which can be scratched by heat sink and make electrical connection. \$\endgroup\$
    – Justme
    Commented Jan 11, 2022 at 18:28
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    \$\begingroup\$ A continuity test that shows continuity is a good indication of "not safe," but a lack of continuity by such a test is not a good indication of "safe." \$\endgroup\$
    – user80875
    Commented Jan 11, 2022 at 19:40
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    \$\begingroup\$ The cans often have insulating varnish on them. This will protect against accidental shorts, but it can be scratched off, and then the metal is exposed. You can test continuity with both probes on the cap, there should be no continuity. But a little scratch will make the multimeter beep. \$\endgroup\$
    – bobflux
    Commented Jan 11, 2022 at 20:03
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No. It is not safe. The metal can may connect directly or via electrolyte to the actual terminals. The metal can should not be assumed to be electrically floating or insulated.

Source 1, section "Insulation and grounding"

Source 2, section "Case potential"

Source 3, section "Electrical isolation of the capacitor"

Source 4, section "Electrical precautions"

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  • \$\begingroup\$ industrial.panasonic.com/cdbs/www-data/pdf/RDE0000/… seems to indicate that it's floating. \$\endgroup\$
    – Aaron
    Commented Jan 11, 2022 at 18:33
  • \$\begingroup\$ -- at least for their designs. \$\endgroup\$
    – Aaron
    Commented Jan 11, 2022 at 18:38
  • \$\begingroup\$ I think your answer is probably the most correct, but I think it could be better explained, so as to be a good answer for others. The first source says the case is connected, but the others (including mine) sources are long and indicate that the case is floating, but it's not a good idea to connect to it, and that they need vent clearance. \$\endgroup\$
    – Aaron
    Commented Jan 11, 2022 at 18:47
  • \$\begingroup\$ @Aaron I opened your link : "3.2 Electrical precautions(1) Avoid touching the terminals of a capacitor as a possible electric shock could result. The exposed aluminum case is not insulated and could also cause electric shock if touched." \$\endgroup\$
    – Justme
    Commented Jan 11, 2022 at 19:32
  • \$\begingroup\$ Source 3 of your answer on page 21 shows it best, I think. It's not fully floating, but is also not directly connected, they show it with a "phantom" resistor to the case. I'd recommend showing something like this in your answer, to show why your answer is correct. \$\endgroup\$
    – Aaron
    Commented Jan 11, 2022 at 19:50

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