# How to tell if a capacitor is still good?

I was replacing a 400v 120uf capacitor in a power supply (ac 120v-19v DC 4.62 amps) well I was a dumb ass and stuck in backwards somehow.

I tested the dc out end while it was still plugged in and got 0.07 volts.

As far as I can tell although being plugged in for 2 minutes (approx) it did not get boiling hot (was barely warm when I reopened it).

Upon visual inspection there does not appear to be any bulging or cracks.

I don't just want to turn it around have it explode, is there a way to check and see its still safe? Is it even likely to be? From what I've read people have mixed opinions but the general consensus is how long vs how many volts, is there a way to be certain?

Realistically I don't care if I just toss it I'm more interested in future so I can recycle parts and components safely.

• is there a way to be certain? ... yes, there is, throw the capacitor away – jsotola Dec 12 '18 at 4:31
• It's not worth the time to test if it's still functional, really. There are failure modes that don't involve the electrolyte boiling, so the fact that it's not hot doesn't necessarily mean it's fine. – Hearth Dec 12 '18 at 4:54
• Normally I would agree however in this case I really just need a crappy but working power supply to test some old laptops. I don't really care if it fails a year or even a month from now... I just don't want to cause an explosion in my apartment lol – Nareik Seivad Dec 12 '18 at 6:31
• Modern elco caps don't really explode, they just vent. If you're ok with a possible PSU failure, and it's no problem to air the room out, just keep the cap. – Dmitry Grigoryev Dec 12 '18 at 8:57
• Where was the capacitor in the circuit when it was connected backwards? Was it on the primary side (120VAC -> 170VDC), or on the secondary (19VDC)? – marcelm Dec 12 '18 at 11:50