new caps reading low on the capacitance meter.

[hydrive]

Hi, I had two capacitors that were exploded on my motherboard, allthough it seemed to still work ok but I wanted to replace them so I removed the exploded capacitors and ordered replacement ones on ebay. Before I installed them I wanted to ensure they were functioning properly, so I tested them with a capacitance meter.

One of the ones that exploded was rated at 1000 uF, 16 V. I ordered 5 of them on ebay and when I measured them with the capacitance meter, they were as follows:
867 uF
818 uF
930 uF
870 uF
816 uF

Since the reading seemed rather low I checked the listing out again, and I notice that it says Tolerance is + or – 20%. Does that mean they are good if they read anywhere from 800 uF, to 1200 uF? Or does that mean I purchased low quality caps since the tolerance is so high? They do not have any brand printed on them but the spec sheet says the series is NHG, so I googled it and I believe they are made by Panasonic. Would these be worth installing or is the capacitance too low?

The other one that blew was 820 uF, 6.3 V. I ordered four of them (from a different ebay seller) and I measured the capacitance and got the following readings:
890 uF
890 uF
897 uF
894 uF
These all seem rather high. These are Nichicon HN capacitors. Is it safe to use them even though they are measuring a bit higher than the rating?

Please clarify for me!

[retiredcaps]

Re: new caps reading low on the capacitance meter.

Probably 98% of the capacitors on ebay are fake.

Since you live in the USA, you have cheap and reliable distributors that sell genuine capacitors with low cost shipping and quick delivery times (usually within 2 days).

Digikey, Mouser, and badcaps.net all meet the above criteria.

[Kiriakos GR]

Re: new caps reading low on the capacitance meter.

Does this capacitance meter have a name ?

[hydrive]

Re: new caps reading low on the capacitance meter.

The meter I am using is an old meter, but it seems to work just fine. I have tested lots of other caps and the rating is always very close to what it says on the label. But the meter is branded as follows: BK Precision, dynascan corp, 820 capacitance meter.

Retiredcaps- Thanks for the info on the suppliers. I will keep that in mind for future projects.

Given that info, I now assume that the the no name caps I ordered are junk especially since the rating is so low. Still not sure about the Nichicon ones I ordered from ebay. Lets say hypothetically I purchased 4 of them from a recommendable source, (820 uF, 16 volts). If I measured them with the meter would it be uncommon for them to be slightley higher, such as in the 890 range?

[Kiriakos GR]

Re: new caps reading low on the capacitance meter.

Your meter is made at 1978 and looks to have 4% accuracy.
At 1000uF you will have +/- 40uF error, plus it needs 10-30 seconds so to setle down.

Not the best choice for true capacity comparisons.

[PeteS in CA]

Re: new caps reading low on the capacitance meter.

Re the supposed Nichicon HNs, that they are all reading high suggests the possibility that they are fakes whose electrolyte lacks stabilizers to prevent the electrolyte from attacking and thinning the aluminum oxide layer (the dielectric in an electrolytic capacitor). IF that is the case, thinning the oxide layer would have two effects: 1.) decreasing its true maximum voltage (and ongoing deterioration would eventually thin the layer to the point of causing the cap to vent); 2.) causing the capacitance to increase (dielectric thickness and capacitance value are inversely related).

If you could post pix of the supposed HN caps, showing all markings, the top vent and the rubber bung, folks here could give you a better idea about the likelihood of the parts being fake or real.

[bigbeark]

Re: new caps reading low on the capacitance meter.

Probably 98% of the capacitors on ebay are fake.

Since you live in the USA, you have cheap and reliable distributors that sell genuine capacitors with low cost shipping and quick delivery times (usually within 2 days).

Digikey, Mouser, and badcaps.net all meet the above criteria.

Not to deny your point entirely, but sometimes you need an odd-sized cap that is not available through the normal distribution channels. Typically it is a higher UF and voltage in an 8 or 10mm can. Surprisingly, these are seldom faked. They will be old stock however.

I have had good luck sourcing FJ series Panasonic caps via Ebay. They have the precut short leads and were obviously intended for some OEM production run but were surplus.

I always test new caps with my ESR and capacitance meters. I have only had one fake experience: some Panny WG 2200uf 16v 10mm. They all measured 1500uf and the ESRs were all over the place. Never dealt with that seller again.

Otherwise, I source caps via Mouser, Topcat & Digi-Key as recommended. A lot quicker and no surprises!