Lifetime calculations for electrolythic caps - diyAudio
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Old 13th June 2005, 01:24 PM   #1
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For professional applications, 20000 hours is really an absolute minimum, but with derating standard caps will cut this.
Bruno: Are you saying that the caps used on your modules have 20000 hours spec'ed lifespan?
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Old 13th June 2005, 01:34 PM   #2
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Originally posted by Lars Clausen


Bruno: Are you saying that the caps used on your modules have this spec'ed lifespan?
Please read the explanation again. I'll try to clarify. Lifetime of an electrolytic capacitor is a function of ambient temperature and ripple current. The lifetime spec given in a data sheet is one single point from this function. Because the function further evolves identically for all capacitors, it is not plotted. Like in a data sheet for resistors there is no graph for current vs voltage.

Thus, extrapolating from this one data point it can be shown that the caps I'm using (which are specified as 5000hrs at 85 degrees) have over 50k hours in them in the conditions at which I use them.
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Old 13th June 2005, 01:39 PM   #3
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Originally posted by Lars Clausen
About EMI / RFI we made huge reductions 2 years ago when we introduced ver 2.1. Of course improving step by step since then. And we are at comparable levels with the other Class D amplifiers on the market, not only from Bruno and Jan-Peter, but in general.
Our modules are around 20dB better than the legal limits. This margin is necessary to insure users have equally good radio reception with our modules compared to a linear amplifier, even if the antenna runs parallel to the speaker wires (not unusual). This level is unparallelled by any competitor.
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Old 13th June 2005, 01:46 PM   #4
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Thus, extrapolating from this one data point it can be shown that the caps I'm using (which are specified as 5000hrs at 85 degrees) have over 50k hours in them in the conditions at which I use them.
Can you show us how you made this calculation? And also give a brand and type of capacitors you are using? 50.000 Hrs that's very impressing

Quote:
Our modules are around 20dB better than the legal limits.
Sounds very impressing. What legal limit are you using for this?
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Old 13th June 2005, 02:13 PM   #5
Electrons are yellow and more is better!
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Quote:
Originally posted by Bruno Putzeys
Lifetime of an electrolytic capacitor is a function of ambient temperature and ripple current. The lifetime spec given in a data sheet is one single point from this function....
Lifetime is really difficult to calculate if you don't already know the results.

At work we had a low price product and suddenly the lifetime was less than 12 months, very irritating becauase of the product garantee. At that time I started to investigate the lifetime and the conclusion was that the caps should last 6-10 months but in real life it was 3-5 years.

So our problem was that suddenly our caps had become worse but within specs. After that we changed brand to Rubycon and we got much better results. Later we also made the design run cooler, less than 60 deg C.

At the moment we have no dried up caps at all.

So, keep the caps cool and you will have no problems with lifetime.
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Old 13th June 2005, 02:19 PM   #6
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Sorry to butt in, I have a question regarding the life time calculations you refer to:

Do you measure the frequency content in the ripple current, or do you “just” use the fundamental switching frequency as ripple frequency for the calculation. I ask because I’m working (at work ) with life time estimations for electrolytic caps in switching applications (SMPS).

I ask because I have used ceramics exclusively until now.

Thanks

\Jens
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Old 13th June 2005, 02:41 PM   #7
Electrons are yellow and more is better!
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Jens, the main thing is to get an idea of how warm or hot the cap will be. This is typical experience thing but I'm sure it's possible to choose caps with taste.
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Old 13th June 2005, 02:53 PM   #8
Electrons are yellow and more is better!
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http://www.elna.co.jp/en/ct/pdf/al_tece.pdf

Pretty good.
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