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Capacitor life

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 14 August, 2009 » Capacitor life « Previous Next »

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echase
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Username: echase

Post Number: 224
Registered: 07-2007

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Posted on Sunday, 02 August, 2009 - 11:45 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I bought a new PC motherboard and noticed that many brands are prominently advertising the great virtues of Japanese solid capacitors with 5000 hours life. One of the spin offs from being trained as a Reliability Engineer is that I know immediately that there are 8760 hours in a year. So 5000 hours will not last a full year of constant running. So it does not seem to me like much of a claim to make.

I assume the catch is that that the conditions under which the 5000 hours is measured is not normal running but anyone know the real story?
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echase
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Username: echase

Post Number: 226
Registered: 07-2007

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Posted on Monday, 03 August, 2009 - 10:47 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Think I can answer my own question. Looking in an RS catalogue I see that many electrolytics have 2000-10000 hours lives quoted, but all are at elevated temperatures e.g. typical non solid one is at 85C but solids at say 105C. So it’s an accelerated life test result, possibly at full voltage.

If I were the motherboard marketing man I’d work it out at a typical operating temperature and voltage and write it as N years at say 50C instead to make it sound better.
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kevinbrunt
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Post Number: 72
Registered: 02-2007

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Posted on Monday, 03 August, 2009 - 12:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I was watching someone investigate a failed electrolytic in a charger for a computer battery only last Saturday. It had gone resistive and was burning up the insulation.....

The capacitor was almost certainly in the original build, as it had a date code for 1963.
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green
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Username: green

Post Number: 85
Registered: 03-2009


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Posted on Monday, 03 August, 2009 - 10:52 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Just goes to show we have pretty short bath tubs these days ... products are supposed to last at least the warranty period !. However at 85 degrees C, i would also expect to fail. In the old days we often talked of capacitors becoming depolarised or "dried out". It is a bit of a strange thought. but how can a hermetically sealed device ... dry out ?.

Boy, am I glad they still sell CV448 diodes, they may not work too well but they sure looked pretty. Oh how I loved the matte black finish of the OC71 and that really cute red dot. Also I loved the adaptability, in that if you wanted an OCP71 light sensor you merely scraped the black paint off an OC71 .... how's that for multi-purpose ?.

The other thing I miss from my early test department days, when I was 14, was the smell of a failed selenium rectifier. Not many components have such a sophisticated failure indicator !

green
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zeitghost
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Username: zeitghost

Post Number: 1311
Registered: 01-2006

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Posted on Tuesday, 04 August, 2009 - 08:38 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

They dry out because they're not hermetically sealed.

Also, in the old days, there wasn't the frenetic washing that goes on these days to get the flux off the pcb...

Electrolytics really don't like being washed all that much...

Surface mount electrolytics appear to be the least reliable of the lot... how many camcorders etc. have been written off because the MTTF of the SM electrolytics is 1 day after the warranty runs out?

Ah. The dead fish smell of the failing selenium rectifier... how I don't miss it... :-)
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echase
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Username: echase

Post Number: 227
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Posted on Tuesday, 04 August, 2009 - 10:02 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I suspect that what happened was that motherboard manufacturer 1 said I am fitting top quality 5000 hr at 105C capacitors so I will mention it in my marketing.

Manufacturer 2 thought, if he is doing it I will do the same.

Manufacturer 3 thought, Ah ha I will fit 5000 at 85C as cheaper, but I can still claim 5000 in my marketing as no one will know the difference.

So it becomes meaningless claim when comparing products.

I also have had several camcorders fail, but mostly due to the tape failing to move properly. Do you think that is due to a capacitor problem? I will never again buy a tape based camcorder, but fortunately there are almost obsolete anyway.


They used to put selenium in some shampoos. That smelled vile too.

(Message edited by echase on 04 August, 2009)

(Message edited by echase on 04 August, 2009)
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joe
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Username: joe

Post Number: 610
Registered: 05-2005

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Posted on Friday, 07 August, 2009 - 01:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I've just been looking at caps on Rapid's site, and saw that they were quoting some as 2000 hrs at 85c.

Looking at the datasheet, it looks like they might be trying to say that after 2000 hrs at 85c, then the cap will be within certain percentages of it's initial specification.

http://www.rapidonline.com/netalogue/specs/11-3100e.pdf

Could be wrong tho.

Joe
Do one thing each day that scares you – work here !

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