Nippon Chemi-Con KMH fakes?

[quicknick]

Last autumn I bought from someone eight 10,000uF/100V capacitors, Nippon Chemi-Con KMH series that should've been brand new... They didn't look like brand new to me when they arrived but also I couldn't find signs they were used... just some scratches, maybe from storage.

Most important, two of them were a bit shorter than the other 6 (45mm vs 50mm). But the price was very good and I asked no questions, just started using them right away as filter caps in my amplifier power supply (four on each channel, two per rail).

A couple of months later, while doing some re-wiring inside the amp, noticed that 6 of the caps (all the taller ones) have slightly bulged across the top... I thought I somehow abused them during some high power tests i've run earlier, and I hoped they will last for a while like that. But last week I opened the case and found out the 6 bad ones swelled even more (while the 2 smaller ones are still in perfect shape). I guess this rules out the possibility that I damaged the caps in the first place.

Fearing they might burst inside the case, I took out the bulged caps today. I'm only running 2x10,000uF per channel now (the 'good' Chemi-Cons on one channel, some cheap Chinese caps on the other).

The first things I noticed after unsoldering them - they seem lighter than when I got them, and if I shake them there's obviously something moving inside, like the "core" has dried and shrunk and is banging the walls of the can...

I tried to find some info about the Chemi-Cons, but there's no 10,000uF/100V capacitor in the KMH datasheet... In fact the largest is 4,700uF at 100V. So I guess, if the six caps are fakes the remaining ones are as well, just better quality. Below are some pics of the suspicious caps - don't mind the red stuff at the bottom, it's silicone glue that kept them tight to the PCB... I striped the sleeve from the one at the left, was going to open the case but I'm not so sure now, maybe there's high pressure inside...

[PCBONEZ]

Re: Nippon Chemi-Con KMH fakes?

Are in data sheet:


Don't look fake.
May be really OLD though.

[quicknick]

Re: Nippon Chemi-Con KMH fakes?

Thanks for that datasheet, I only knew about this one:


But... case size is specified at 40x80 in the datasheet for the 10,000uF/100V, and my caps only measure 35x50. Isn't that a bit strange?

[PCBONEZ]

Re: Nippon Chemi-Con KMH fakes?

It's not that unusual to find a can size that's not in the data sheet.
Most manufacturers will build custom sizes if the order is large enough to justify it.
Without something else being wrong also that doesn't prove anything.

That said:
Since my last post I looked at a few Chemicons around here and the date code isn't in the same one-line format as those you have. [A7088]
That might be because:
- They are fake.
- They are really old.
- They use a different date format on huge caps. [Biggest I looked at are 12.5mm]

Date codes on mine are two lines like:
5 (7)
8 R

I know the "5" is 2005 by dates on other parts.
I -think- the "7" is the month which would also be consistent with other dates.
I know Chemicon has used that style code has been used since at least 2001 [from other caps around here].

If it is Chemicon with an old style date code my guess would be that "7088" means the 88th day of 1997 or 1987.

Regardless, they are obviously duds.
.

[quicknick]

Re: Nippon Chemi-Con KMH fakes?

Bad luck seems to follow me when it comes to caps. These Chemi-Cons just arrived to me from the US, and they look (and feel) somewhat different of what I expected. Of the 12 units, most of them have some sort of residue on the rubber pad at the bottom, something resembling wax but a bit harder (can be scraped by fingernail though). It has a faint smell, not like electrolyte but more like something petroleum-based. Any ideas on what this might be?

Second, I think the markings should be of better quality.

Third, all of them have an off-axis weigth center. That is, if i lay them horizontally on a flat surface, they have a very strong tendency to roll over and rest with the "negative" stripe facing down ...

Anyway, this is the last time I'm buying caps from other sources than well-renowned parts shops...

Should I crack open one of the cases to check for Chinese 4700uF/35V inside the big cans?

[kc8adu]

Re: Nippon Chemi-Con KMH fakes?

something is not right about those!
it would be interesting to see what the esr,capaitance,and leakage readings are.
it is strange that they tend to roll to the negative side too.
i wonder if ncc specs the weight in the spec sheet?
that could tell us if something is not right.
if you open one up pics would be cool.
if these are fakes we also would like to know where you got them.

[quicknick]

Re: Nippon Chemi-Con KMH fakes?

Well, I cleaned the "bungs" with cotton swabs and isopropyl alcohol and they look normal now (see pic).

Any method to measure capacitance and leakage? (ESR would be hard to measure without an ESR meter I guess). I figure the capacitance could be found out by measuring the time it takes to charge the cap to a certain voltage thorugh a resistor, but what voltage should I use and what's the formula that gives me the C?

[quicknick]

Re: Nippon Chemi-Con KMH fakes?

Found out the answer to one of the above, C=T/R. I used a 2 Kohm resistance and a 66V supply, it takes about 32 seconds for a cap to reach 42V (63% of supply voltage), that means around 16000uF. Not fakes then?

[Gianni]

Re: Nippon Chemi-Con KMH fakes?

You need an oscilloscope, a PS and resistor. I think you can test them at nominal value or lower value(for 16V caps use 10-12V).
A practical way I use to calculate the time in this one:

Time= (Capacitance x Voltage)/Current.

The time you calculate it is not the complete charge but it is 0.63% of applied voltage.
In the pics I attached you can see the voltage on 1000uF with 1Kohm in series during charge at 10V.
The current is 10V/1000ohm=10mA
In this case time is 1 second because T=(0.001F*10V)/(0.01A)

From the pics you can see that after 1 second the voltage on the cap is about 6.4V, which is 0.63% of 10V.
The complete charge, IIRC, takes around 4.5 times of the time given by the formula T=(C x V)/I
Don't ask me to explain theory... too much rust in my brain.

Anyway I think the best way to check caps is to use an LCR meter or ESR meter.

Ciao
Gianni

[Gianni]

Re: Nippon Chemi-Con KMH fakes?

I didn't see your reply because I was testing my theory.

From your result at least you know the value should be right but I don't know if it is enough to say "no fakes".

In my previous post I wrote a wrong number, the charge is not 0.63% but 63% of applied voltage.

Ciao
Gianni

[goodpsusearch]

Re: Nippon Chemi-Con KMH fakes?

Hello. I came across those bulging caps today.

I was very disappointed to find out they are Nippon Chemi-Con.

They are KMH and like the original poster says if I shake them

there's obviously something moving inside, like the "core" has dried and shrunk and is banging the walls of the can...

I got some photos with my mobile.