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Old 10-12-2020, 12:12 PM   #1
AlbertRoss
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Default Caps With High uF

Hi,
I've removed some electrolytic caps from a Hi-Fi power supply which are Asia'x? Two of them both 470uF 10V have a high uF value, one reads 693.6uF ESR- 0.12R and the other one reads 670uF ESR-0.12R?
I presume caps have a tolerance, either 10 or 20% so even at say 20% they would be still over their uF limit? What effect will these have, will they still work?

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Albert.
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Old 10-12-2020, 12:14 PM   #2
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Default Re: Caps With High uF

Usually if the capacity measures higher they are bad.
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Old 10-12-2020, 04:15 PM   #3
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Default Re: Caps With High uF

IIRC, if a 'lytic cap measures well out of tolerance high that means the aluminum oxide dielectric layer has thinned, increasing the capacitance, but reducing its actual breakdown voltage. The typical tolerance for an electrolytic capacitor is +/-20%, 564uF max for 470uF parts.

You might be able to re-form these parts, though they're a junker brand not worth the effort except as a learning experience.
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Old 10-13-2020, 04:06 AM   #4
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Default Re: Caps With High uF

Hi, thanks for your help. I've not seen these Axia'x before and they came out of a Panasonic SA-AKX16 CD Stereo System which is completely dead. Am I correct in saying that if all the other caps were good on this board but I left these 470uF high value caps in place, would that have a serious effect on the unit?

Albert.
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Old 10-13-2020, 08:47 AM   #5
stj
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Default Re: Caps With High uF

electrical leakage is BAD, change them or something could get damaged.
or the caps could heat up and potentially explode or burst open and spew electrolyte and bits of paper all over the place.
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Old 10-14-2020, 03:45 PM   #6
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Default Re: Caps With High uF

I replace all caps that are not within spec.
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Old 10-14-2020, 08:17 PM   #7
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Default Re: Caps With High uF

Quote:
Originally Posted by CapLeaker View Post
I replace all caps that are not within spec.
+1

A bad cap is not going to get better over time. Quite the opposite - it will only get worse. So it's indeed better to replace it.

Quote:
Originally Posted by stj View Post
or the caps could heat up and potentially explode or burst open and spew electrolyte and bits of paper all over the place.
As long as the cap(s) have proper vent stamps, none of that should happen and the cap should vent "gracefully". But you can never be 100%, of course.

Fun fact: Sacon FZ caps have their stamps done from the inside the case, which causes them to burst the vent rather violently when they outgas (sounds like a fire cracker going off, really.) Although you won't find then ejecting paper, they often spew electrolyte quite far. I tried it last week with one and it threw electrolyte spray/mist/droplets more than a few cm / inches away.

Quote:
Originally Posted by PeteS in CA View Post
You might be able to re-form these parts, though they're a junker brand not worth the effort except as a learning experience.
I've tried that before with my cap reforming experiments.

Unfortunately, I haven't seen any caps with high capacitance get healed from this.

Last edited by momaka; 10-14-2020 at 08:19 PM..
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Old 10-16-2020, 07:16 AM   #8
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Default Re: Caps With High uF

I see the same thing with the faulty Nichicon HM caps... Supposed to be 3300uf
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