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The title says it all, I'm wondering if an electrolytic (or any other type) capacitor needs to be bulged to be bad?

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No, they don't. There are various failure mechanisms, some of which don't exhibit bulging of the case. Also bulging is pretty much limited to electrolytics. Ceramics and other types don't do that because there isn't liquid electrolyte inside that can be electrolyzed, emit gasses, and thereby build up pressure.

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    \$\begingroup\$ otoh bulged elcos can be still "good" i.e. they have the necessary capacity. \$\endgroup\$
    – PlasmaHH
    Jan 20, 2015 at 14:22
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    \$\begingroup\$ @Plasm: A bulged capacitor is never "good". Yes, they can still have the necessary electrical properties for the circuit to continue functioning. But, some damage has already occured and some margin already used up. The cap is now closer to (possibly catastrophic) failure than it was when new, and stresses that would otherwise be OK might tip it over the edge. \$\endgroup\$ Jan 20, 2015 at 14:25
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    \$\begingroup\$ This is why I wrote it with quotes. \$\endgroup\$
    – PlasmaHH
    Jan 20, 2015 at 14:36
  • \$\begingroup\$ @OlinLathrop: My former employer had a television set which was damaged by lightning, and still worked fine except for smoke coming out the top. During operation, one of the resistors inside was glowing (and smoking). The insurance company wrote the set off as a loss and paid to replace it (probably figuring it would pose a fire risk otherwise) but I found it interesting that even with a resistor that was glowing (and whatever other damage was making it glow) the set worked perfectly in all other regards. \$\endgroup\$
    – supercat
    Jan 20, 2015 at 18:00
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    \$\begingroup\$ tantalums are probably the most fun, and explode very satisfyingly. \$\endgroup\$
    – abligh
    Jan 20, 2015 at 23:38

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