Author Topic: Verifying ceramic capacitor voltage rating  (Read 1838 times)

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Offline StefanHammingaTopic starter

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Verifying ceramic capacitor voltage rating
« on: January 25, 2019, 01:16:01 pm »
So I bought some 100uF / 100V (supposedly) 5750 20% X5R capacitors from AliExpress. I normally buy my parts from Mouser, Digikey, etc, but I couldn't resist buying a few knowing the specs sound too good to be true. The item can still be found for sale here:

https://www.aliexpress.com/item/5pcs-SMD-capacitor-2220-100UF-100V-107M-5750-20-X5R/32636203607.html

Surprisingly the capacitance of the first few are in the 85-90 uF range, so not much wrong there. I'd love to find some indication of the voltage rating (and if possible other specs), preferably without any plucking of ceramic shards from my forehead. Any way to verify the voltage rating non-destructively?
 

Offline OwO

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Re: Verifying ceramic capacitor voltage rating
« Reply #1 on: January 25, 2019, 01:26:29 pm »
Any way to verify the voltage rating non-destructively?
Probably not, but a simple breakdown voltage test should tell you if the rating is in the right ballpark. I'd expect breakdown voltage to be at least 20% higher than rating.
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Offline GreggD

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Re: Verifying ceramic capacitor voltage rating
« Reply #2 on: January 25, 2019, 01:59:27 pm »
Cap makers say they test to 2X the rated voltage but won't say just how they test them.
Yes I too would like to know proper test for voltage.
 

Offline T3sl4co1l

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Re: Verifying ceramic capacitor voltage rating
« Reply #3 on: January 25, 2019, 02:21:17 pm »
Just pull it up with a resistor, say 100k.  Measure leakage current.  Consider this a destructive test; if leakage increases suddenly and massively, throw it away. :)

Bigger priority: measure capacitance under bias.  Connect two in series, and bias the "center tap" with a large value resistor.  Measure capacitance of the series pair.  The point where C drops by, say, 30%, is a practical cutoff point for use.

This tests saturation voltage.  Capacitors are never rated in this way, despite it being fundamental to operation; you have to dig through the datasheet or mfg website to find this data, if they have it at all.  Or buy some and characterize yourself.

FYI, very large ceramics (over 1210 / 3225 size) are discouraged for reliability reasons: more likelihood of cracking under thermal and flex stress.  (If you aren't doing anything horrendously expensive, or freakishly important, don't worry about it. :) )

Tim
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Online wraper

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Re: Verifying ceramic capacitor voltage rating
« Reply #4 on: January 25, 2019, 02:33:31 pm »
You won't be able to get the actual voltage they were rated for with good confidence when measuring their breakdown. Ceramic capacitors often survive over 10 times of rated voltage. However you could measure capacitance under bias voltage. Type 2/3 ceramic capacitors drop a lot of their capacitance under voltage. Some of the worst ones (high capacitance and rated voltage for it's size) have less than 20% under rated voltage. So I'd say when around 25-30 % of capacitance is left, it likely would be somewhere around it's rated voltage.
 
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