Author Topic: Ceramic caps from China  (Read 953 times)

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Offline Discotech

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Ceramic caps from China
« on: August 18, 2018, 06:49:27 am »
Some of the caps I've been testing today have been way out of tolerance

1nF = 1.4nF
4.7nF = 6.8nF
150pF = 100pF
100nF = 50nF
1.5nF = 2nF

the other 70% of the bundle were within tolerance

But I don't understand how these ones can be so far out they're in the next or previous band, is it an issue when the numbers are printed on them and they get the wrong ones printed ? Is this common with caps from China ? Better to buy from Farnell/Mouser if you want better accuracy I guess ?
 

Offline homebrew

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Re: Ceramic caps from China
« Reply #1 on: August 18, 2018, 07:17:51 am »
What is the exact specification of the capacitors?
How did you measure the capacitance?

Generally speaking, I would ONLY buy from reliable sources anyway.That said, many reliable electronic parts are manufactured in China ... So rather your specific source than the country of origin would be the issue ...
 

Offline Discotech

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Re: Ceramic caps from China
« Reply #2 on: August 18, 2018, 07:28:15 am »
What is the exact specification of the capacitors?
How did you measure the capacitance?

Generally speaking, I would ONLY buy from reliable sources anyway.That said, many reliable electronic parts are manufactured in China ... So rather your specific source than the country of origin would be the issue ...

The numbers on left were supposed specified values, with the numbers on the right being what they were closer to

Used both my DMM and GM328 Tester on the first few as I was thinking it was possibly mistaken calibration on the tester but when the DMM was showing pretty much identical values I figured it must be the caps that have incorrect numbers printed on them

I'm not too fussed as they were cheap from aliexpress, it was like £1 for 300 and the majority were within spec but the ones out of spec were way out so I was wondering if it's a common issue ?
 

Offline bson

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Re: Ceramic caps from China
« Reply #3 on: August 18, 2018, 07:38:55 am »
The tester may not have any accuracy to speak of at such small values.
What is the dielectric class and voltage rating?  Maybe they're derated for a higher voltage than the tester uses.
 

Offline floobydust

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Re: Ceramic caps from China
« Reply #4 on: August 18, 2018, 07:39:12 am »
I too find the cheapola cap values are all over the place. Expensive parts are all about -15% and vanilla parts are +/-30% of rated value.
 

Offline Discotech

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Re: Ceramic caps from China
« Reply #5 on: August 18, 2018, 07:57:47 am »
The tester may not have any accuracy to speak of at such small values.
What is the dielectric class and voltage rating?  Maybe they're derated for a higher voltage than the tester uses.

50v X7

Tester only uses 9v  :-//
 

Offline T3sl4co1l

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Re: Ceramic caps from China
« Reply #6 on: August 18, 2018, 10:06:20 am »
Nice thing about caps is they are almost never labeled, so you can "counterfeit" by merely swapping labels on the reel, or stock numbers even.

Ditto for voltage.  You could get an 0805 10nF that's 16V (contains a few very closely spaced plates, and a lot of unused ceramic), or 100V+ (the entire height is filled by more, and widely spaced, plates).  No idea until you do a C(V) test.

Tim
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Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
 

Offline LukeW

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Re: Ceramic caps from China
« Reply #7 on: August 18, 2018, 08:09:28 pm »
What is the specified tolerance of the caps you ordered?
What’s the dielectric type you ordered?

What is the rated voltage of the cap and what voltage are you measuring the capacitance at? What temperature?

It is not yet clear that you did not get what you asked for.
 

Online wraper

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Re: Ceramic caps from China
« Reply #8 on: August 18, 2018, 08:18:44 pm »
Is this an SMD capacitor assortment? Most likely they were just mislabeled.
 

Offline treez

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Re: Ceramic caps from China
« Reply #9 on: August 18, 2018, 08:20:51 pm »
I  think what you got sounds ok...if you want accuracy in ceramic, you need C0G dielectric
 

Online imo

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Re: Ceramic caps from China
« Reply #10 on: August 18, 2018, 08:22:41 pm »
I got a shortwave cw transceiver kit ($18) from China, and ALL the ceramic (small brown discs) capacitors were around 50-100% off. They were labeled with the value. Thus I replaced all the caps and resistors and it worked fine.
 

Online wraper

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Re: Ceramic caps from China
« Reply #11 on: August 18, 2018, 08:22:57 pm »
I  think what you got sounds ok...if you want accuracy in ceramic, you need C0G dielectric
It's not, and 150pF most likely would be C0G anyway. Also very unlikely that type 2 and 3 ceramic caps would go that much upwards in their capacitance in any circumstances.
« Last Edit: August 18, 2018, 08:25:41 pm by wraper »
 

Offline Discotech

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Offline Old Printer

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Re: Ceramic caps from China
« Reply #13 on: August 18, 2018, 11:34:26 pm »
I have read that "run of the mill" ceramic capacitors have a typical tolorence of -20% to +80%. I thought that was wacky, but have seen that in a few places. This was not in reference to any particular brand.
 

Offline Audioguru

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Re: Ceramic caps from China
« Reply #14 on: August 18, 2018, 11:50:11 pm »
Which is trustworthy? A Chinese capacitor with no-name-brand that was made by someone who knows little about capacitors and made by him in his basement? Or a capacitor made by a trusted international company in their factory in China? Their spec's and costs are a "little" different.

"Ali" companies are Chinese like "ebay". Who knows if they buy good stuff or junk. They both sell cheap stuff.
 

Offline rstofer

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Re: Ceramic caps from China
« Reply #15 on: August 19, 2018, 05:33:45 am »
Here is a page from DigiKey - note that one category of tolerance is 0,+100%

https://www.digikey.com/products/en/capacitors/ceramic-capacitors/60

It could be that all of your capacitors are within that tolerance.  The question is: what was the specified tolerance?

The assortment only costs $1.40 USD so I wouldn't have high expectations.
 

Online wraper

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Re: Ceramic caps from China
« Reply #16 on: August 19, 2018, 06:02:57 am »
Here is a page from DigiKey - note that one category of tolerance is 0,+100%

https://www.digikey.com/products/en/capacitors/ceramic-capacitors/60

It could be that all of your capacitors are within that tolerance.  The question is: what was the specified tolerance?

The assortment only costs $1.40 USD so I wouldn't have high expectations.
I don't think it's possible to get 1-2n low voltage capacitors with super unstable Y5V, Z5U (type 3) ceramic. But it's quiet easy to check. Just hold a capacitor with fingers while measuring and capacitance should go down a lot due to heat transfer from fingers. Or heat some other way.
 

Offline mzzj

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Re: Ceramic caps from China
« Reply #17 on: August 19, 2018, 06:10:57 am »

I don't think it's possible to get 1-2n low voltage capacitors with super unstable Y5V, Z5U (type 3) ceramic. But it's quiet easy to check. Just hold a capacitor with fingers while measuring and capacitance should go down a lot due to heat transfer from fingers. Or heat some other way.
Just hold my beer:  ;D https://www.digikey.com/products/en/capacitors/ceramic-capacitors/60?k=&pkeyword=&pv14=20&pv14=32&FV=440003%2C44016e%2C44016f%2C440170%2C4401a2%2C440037%2C440006%2C440044%2C440045%2C440007%2C440055%2Cmu1000pF%7C2049%2Cffe0003c%2C380002%2C380014%2C380020&quantity=0&ColumnSort=0&page=1&pageSize=25
 

Online wraper

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Re: Ceramic caps from China
« Reply #18 on: August 19, 2018, 06:29:35 am »

I don't think it's possible to get 1-2n low voltage capacitors with super unstable Y5V, Z5U (type 3) ceramic. But it's quiet easy to check. Just hold a capacitor with fingers while measuring and capacitance should go down a lot due to heat transfer from fingers. Or heat some other way.
Just hold my beer:
Only one part number in stock and that junk costs $ 0.30  :o, LOL. +-20%, though. I wonder who buys that junk at such price.
 

Online bd139

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Re: Ceramic caps from China
« Reply #19 on: August 19, 2018, 06:46:49 am »
Just a heads up on shitty ceramics. A few of the C0G's and X7R's I got from even "multicomp" brands were bags of lies. A bag of MLCC's I bought from China were 50% faulty.

I only buy Vishay / Murata / Kemet stuff from main line distributors now. Costs a lot more but worth it.
 

Offline Discotech

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Re: Ceramic caps from China
« Reply #20 on: August 19, 2018, 07:33:33 am »
Here is a page from DigiKey - note that one category of tolerance is 0,+100%

I don't understand though, do they not do much QA testing on them ?

Surely if you're making caps and you test a bunch and they turn out to be 100nF instead of the 50nF you were expecting it would be easier to just rate them at 100nF instead or do they test after the numbers have been printed and just say "fuck it" if it's nowhere near intended rating ?

+100% tolerance sure seems like a "fuck it" attitude from the manufacturer  :palm:
 

Offline bson

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Re: Ceramic caps from China
« Reply #21 on: August 19, 2018, 08:48:19 am »
Take a look at:
https://en.wikipedia.org/wiki/Ceramic_capacitor#/media/File:MLCC-BME-NME-Kap-Spg-Kurve-engl.svg

So if you want 100nF for the particular BME X7R cap graphed at its rated 50V, it will need to be almost 200nF (maybe 180nF) at 10V.  Class 2 caps have very poor voltage linearity and are intended for bypass and supply filter uses, not resonant circuits...  Add to this the 15-20% (I forget off hand) tempco...  For the X7R's I think you probably got a reasonable product based on your measurements so far.
« Last Edit: August 19, 2018, 08:50:29 am by bson »
 

Offline bson

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Re: Ceramic caps from China
« Reply #22 on: August 19, 2018, 08:52:20 am »
Put on your safety glasses and subject one to 50V to see what happens. :)
 

Offline KE5FX

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Re: Ceramic caps from China
« Reply #23 on: August 19, 2018, 09:10:19 am »
It's almost unthinkable that people aren't relabeling MLCCs under the table, given how apocalyptically-f***ed the market is.  If you're a Chinese distributor with a warehouse full of 82 nF caps, and everybody wants 100 nF, well...
 

Offline floobydust

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Re: Ceramic caps from China
« Reply #24 on: August 19, 2018, 10:20:56 am »
Just a note- capacitance meters can give confusing results.
It depends on the test voltages and firmware algorithm (single or dual-slope), because the voltage coefficient of capacitance and dielectric non-linearity can show up, more or less.

I'm wondering if the chinese are selling rejects (high/low out of tolerance) or they have poor quality control on the ceramic powders, or if these are from small ma and pa shops.
 
 


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