How safe is an electrolytic capacitor after reverse polarity ?

[MathWizard]

I just had a new 10uF 50V JRB -40-105C cap put in backwards on a 5V rail, for about 2-5 minutes. It's not even warm, but I've blown up 2-3 caps with reverse polarity over the past few years. I didn't take long either, on a 12V rail and a -12V rail.

So how healthy might it still be ? It's only been used on a breadboard a few times.

[Vovk_Z]

Put it under positive voltage (>=1/2 rated) for several minutes or longer and measure a leakage current. If leakage current is very small (<1 uA) then possibly it is fine.

[amyk]

If they weren't totally destroyed by the reverse bias, putting them back in the right way and keeping voltage on them (while monitoring the current) should see them reform their dielectric again.

[T3sl4co1l]

5V is enough that there was probably some internal reaction. But evidently not much if they didn't get warm from it.

Usually, reversal of a few volts is acceptable, or some percentage depending on rating.  Chemically, the cathode foil has some natural oxide, not nearly so well crafted as the anode, but enough to hold off a couple volts; also give or take the ionic double layer effect.

At worst, some reforming will be fine.

Tim

[MathWizard]

Ok I'll try it again with a series resistor, and leave it for a while, see if it's capacitance changes or if it leaks.

My main worry is it blows up on the breadboard and hits me in the eye, but I'll try it anyways. Thanks

[macboy]

A 10 uF 50 V cap costs what, 10 cents? To be practical about it, junk it and take another out of the parts box.
If you really need to know if it's good, compare capacitance, ESR, and leakage current to a known good one.

[RayRay]

Ok I'll try it again with a series resistor, and leave it for a while, see if it's capacitance changes or if it leaks.

My main worry is it blows up on the breadboard and hits me in the eye, but I'll try it anyways. Thanks

I'd suggest you get yourself a good pair of safety glasses! As well as not stand too closely to a breadboard/circuit board when you suspect things could go badly. But I overall agree with the advice given by macboy. A capacitor is a cheap component that is easy to replace, why insist on continuing to use it and take unnecessary risks?