Author Topic: Testing capacitor leakage current directly  (Read 3702 times)

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Offline Algojervia

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Testing capacitor leakage current directly
« on: November 14, 2016, 09:36:35 am »
So I have some vintage electronics I'm playing around with and got some electrolytic capacitors that I would like to test. I'm planing on getting a real ESR meter but currently I only have one of those Atmega based component tester you can pick up for few bucks at eBay and I don't really know if it is good for anything. There is one old unit I'm considering going all in and try to reform the caps and all that but for the rest I plan to just get replacement caps but it will take a few weeks before I get them so in the meantime I'm have been focusing on my VTVM. It has only one smoothing capacitor rated at 3.3µF and 160 volt that probably should be bad by now. My atmega meter thingy takes a guess at 4.46µF and ESR=21.1? while the BM235 reads 4.39µF and 60M? resistance. So based on the ESR I concluded that this cap was indeed kaput witch in turn made me experiment a bit with reforming without any great success. However I finally decided to connect the DMM in series with the cap and put it in mA and slowly turned up the voltage on my supply. To my surprises it did not register any current what so ever and after a some confusion I turned to nob to µA and got a consistent reading of just about 1-2µA, so I continued up to 160 volt and the current settled around 3µA. Is this a large leakage current? I was expecting something in the mA range. Does this means that this cap it ok after all or does the leakage current manifest itself when some frequency is introduced like the ripple voltages?
 

Offline Totalsolutions

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Re: Testing capacitor leakage current directly
« Reply #1 on: November 14, 2016, 11:54:35 am »
Hi, it could mean you need a real ESR meter after all. I brought mine only a few years ago and find it very useful, YMMV. Thought a capacitor meter would be good enough, should have brought 45 years ago !.  My advice is purchase tools as you need them and will last a while, and stops you pursuring dead ends and reading theads about other so called ESR meters but not really performing any real test. Purchase and move on and enjoy your hobby.

Sent from my GT-N7100 using Tapatalk

Paul
 
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Offline bktemp

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Re: Testing capacitor leakage current directly
« Reply #2 on: November 14, 2016, 12:18:16 pm »
Capacitance, leakage current and ESR are completely different characteristics of a capacitor.
ESR is the series resistance, the value shown on the BM235 is probably the parallel resistance at the measurement frequency.
21ohms ESR is a bit on the high side for modern capacitors, but it may be in spec for an ancient capacitor.
 
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Offline Kalvin

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Re: Testing capacitor leakage current directly
« Reply #3 on: November 14, 2016, 02:37:28 pm »
You can verify the cheap ESR meter by adding a small resistor (like 1ohm or 0.1ohm) in series with the capacitor and see whether the reported ESR reading increases accordingly.
 
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Offline danadak

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Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 
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Offline snarkysparky

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Re: Testing capacitor leakage current directly
« Reply #5 on: November 14, 2016, 02:55:37 pm »
At 160V 3 uA leakage is not a bad capacitor.
 
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Offline Kalvin

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Re: Testing capacitor leakage current directly
« Reply #6 on: November 14, 2016, 03:00:32 pm »
Measuring nanoamps and capacitor leakage current: The eevblog user darksky has a nice project https://www.eevblog.com/forum/projects/nano-amp-meter-with-hx711/ and he has reported to achieve nanoampere resolution. A simpler, fully analog nanoampere meter by dannyf will do the trick as well: https://www.eevblog.com/forum/projects/el-cheapo-micro-ammeter/
 
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Offline kripton2035

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Re: Testing capacitor leakage current directly
« Reply #7 on: November 14, 2016, 04:26:15 pm »
here you have some projects that measure leakage of a capacitor :
http://kripton2035.free.fr/LCR%20meters/lcr-capaleakmete.html
http://kripton2035.free.fr/digital%20esr/esr-sprut-de.html
the later also measures esr and the capacity.
you can invest in a lcr meter but they mainly do not measure leakage, only l,c,r and esr

Offline Algojervia

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Re: Testing capacitor leakage current directly
« Reply #8 on: November 14, 2016, 05:38:07 pm »
Wow, the speed and quality of this forum is sort of unparalleled.  :-+

I'm a bit confused about the applied test voltage from an ESR meter however, a few sites seems to mention that modern meters are not good for caps that are rated at several hundreds of volts and that I need something like a Heathkit IT-11 or IT-28, sadly very hard for me to get my hands on for a decent shipping price. However almost all sites I read about ESR meters does not mention this at all.

Very interesting links to the ammeters projects, I have been thinking about something like that but just haven't come around it yet. But do I understand it correctly when I'm thinking that in this case with the cap I describe the added resolution does not provide much since it already register several µA but that it is more important on smaller/newer caps?
 

Offline bitseeker

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Re: Testing capacitor leakage current directly
« Reply #9 on: November 14, 2016, 09:45:49 pm »
I'm a bit confused about the applied test voltage from an ESR meter however, a few sites seems to mention that modern meters are not good for caps that are rated at several hundreds of volts

It depends what you're measuring. For ESR, you don't necessarily need a high voltage. However, for leakage, you want to be able to apply sufficient voltage to see how much leakage there is at least under operating conditions. For example, testing the leakage of a 500V capacitor isn't very conclusive at 100mV.
I TEA.
 
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Offline David Hess

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Re: Testing capacitor leakage current directly
« Reply #10 on: November 15, 2016, 09:11:22 am »
Measuring nanoamps and capacitor leakage current: The eevblog user darksky has a nice project https://www.eevblog.com/forum/projects/nano-amp-meter-with-hx711/ and he has reported to achieve nanoampere resolution. A simpler, fully analog nanoampere meter by dannyf will do the trick as well: https://www.eevblog.com/forum/projects/el-cheapo-micro-ammeter/

There is a simpler, easier, and higher performance way to do this if you have a reasonable digital voltmeter which is mentioned in your second link.

For a voltmeter, the voltage reading will indicate current through the input shunt resistance so a typical 10 megohm voltmeter will show E/10M or 100 pA/mV.  Most of my meters have at least 0.1mV resolution so when used with this way, they have a resolution of 10pA.  If you need a lower sensitivity and burden voltage, then add an external resistive shunt.
 

Online BravoV

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Re: Testing capacitor leakage current directly
« Reply #11 on: November 15, 2016, 09:30:26 am »
As they're vintage caps, even they're still fine, they need to be soaked in their rated voltage for a while as it needs quite some time to reform.

I did similar measurement using DMM's internal resistance, and by logging the the leakage thru time, you can see the reforming process is slow, detail -> HERE.

Example : The leakage chart result from a NOS polymer cap OSCON at it's rated voltage, at the chart reading, 1 volt equivalent to -> Volt / (10M Ohm DMM internal resistance) -> 0.1uA

« Last Edit: November 15, 2016, 09:32:28 am by BravoV »
 


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