Some capacitor leakage measurements

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Tim

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Tim Williams
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Here are a few things I've measured, not general but as needed.

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John Larkin         Highland Technology, Inc 

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jlarkin

He had me going for awhile there, till I saw that he was using gigundo COGs like 220 nF. ;)

The bad ones were mostly Kemet. These days I don't seem to use a lot of Kemet capacitors compared with Samsung, Murata, and TDK. Kemet does have a quite decent characteristics browser that even has SPICE models. (Dunno how good they are.)

Cheers

Phil Hobbs

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Phil Hobbs

It is often hard to measure leakage current and not dielectric relaxation currents...

Bye

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Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de 

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Uwe Bonnes

Well since he tested only one batch you can always worry that he got a 'good' batch of TDKs and some worse kemets.

There were some comparison graphs of COGs in AoE with some better and some worse... but only IDed as brand a,b and c... or some such.

I do (did) use a lot of those big 10 uF Panasonic film caps.

George H.

Reply to
George Herold

Right. Leakage can take seconds to days to settle down, so there may be no simple value.

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John Larkin         Highland Technology, Inc 

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jlarkin

Somebody here once measured self-discharge of some film caps, over years. I recall discharge levels something like one per cent per year.

I measured one supercap that had a discharge tau of a few months.

The gate voltage of a decent mosfet will stay put, unconnected, for days. Leakages are not many electrons per second.

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John Larkin         Highland Technology, Inc 

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jlarkin

Tom Bruhns. e.g.:

From: snipped-for-privacy@aol.com (Tom Bruhns) Newsgroups: sci.electronics.design Subject: Re: Measuring leakage current of Capacitors Date: 18 Jul 2002 18:16:17 -0700

I should tell you, though, I've kept the little board with the caps still soldered to it. They are still discharging. It's been a while since I measured them, but the last time I did, some two years after they'd been charged, the apparent time constants were on the order of 50 years for the polypropylenes, and about 2.5 years for the polyesters (Mylars). Since it's been about 9 months since I last measured them, it's about time for another measurement. I'll try to remember to do that and post more complete results in the near future.

Modern polyprops are pretty darned low leakage!

Cheers, Tom

(How I remember such stuff so easily is a mystery to me, but it comes in handy.)

Cheers, James

Reply to
dagmargoodboat

Or weeks for supercaps (in regards to the last entry in your other post's link).

Which seem to retain voltage quite well (many months) well below threshold. At room temp. Means a generous derating (say 1.5-2V nominal out of a 2.7V rating) but still handy for some applications.

Tim

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Tim Williams

=========================================

** Must have been some large value polystyrene types.

Lowest tempco and leakage of any film cap.

.... Phil

Reply to
Phil Allison

Teflon might be lower leakage, but the only sources I know of are surplus USSR parts on ebay that are usually physically huge and of unknown and probably quite adventurous history, or by slaughtering a Tektronix scope, which ought to be illegal.

Reply to
Chris Jones

There's still plenty of teflon film cap makers in the US. Teflon caps have high temp ratings, that's about it. It's not the end-all dielectric material.

Reply to
Cydrome Leader

======================

** Like everyone knows ...

noting stciks with Teflon.

.... Phil

Reply to
Phil Allison

Yes, I had seen that there are companies that make them, however there are none at Mouser and there is only one range in digi-key and the largest value is 47pF, so I still consider them hard to get in higher capacitance values.

Do you know of any distributors that stock a good range of them?

I know they are not magical, but probably have slightly less leakage than polystyrene, and certainly a better combination of low leakage and also withstanding soldering temperatures.

Reply to
Chris Jones

Octopart doesn't have show high-value PTFE-dielectric caps in stock anywhere.

Cheers

Phil Hobbs

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Phil Hobbs

===================

ar.

Years ago I went searching for a teflon cap. The only ones I could find were on a audio oriented website. Which besides selling ~$50 teflon caps, suggested that they needed to be conditioned with broad band noise for several days. ('they' being the teflon caps and not the website. :^)

George H.

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George Herold

Does anyone have a use for super-low-leakage caps?

Teflon has a horrible TC, so the voltage on a charged cap will change with temperature. That could look like leakage, or anti-leakage.

Interesting: is the energy conserved after a temperature cycle?

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

===================

ear.

d

Are you asking how much heat is generated in a temperature cycle? That's wh ere any inefficiency ends up.

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  Rick C. 

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Reply to
Ricketty C

Its glass transition is right around room temperature, so CTE and other TCs go nuts in a very inconvenient region.

Should be--if the charge is conserved it can't do any net work on the outside world. I suppose the Coulomb force or the winding pressure could conceivably change the shape or microstructure of the dielectric if it got soft enough to creep.

Cheers

Phil Hobbs

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Phil Hobbs

I was wondering what happens to the charge as it moves around through the glass transition. Fortunately, I don't use teflon caps! FR4 is bad enough.

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John Larkin         Highland Technology, Inc 
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John Larkin

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