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Life expectancy of Aluminum electrolytic capacitor

O

Obelix

Jan 1, 1970
0
I've been looking for a formula describing the life expectancy of Al
Electrolytic Capacitors. I found a couple of sources that descibe life
expectancy based on an exponential relationship with ambient operating
temperature and a linear relationship with operating voltage.

Is there a good source for determining the life of an Al Capacitor?
Does anyone know of a good white paper or similar? I would rather have
a more reliable source than a suppliers website or at least know that
the information is reliable enough.


Thanks,

Carlos
 
R

Robert Baer

Jan 1, 1970
0
Obelix said:
I've been looking for a formula describing the life expectancy of Al
Electrolytic Capacitors. I found a couple of sources that descibe life
expectancy based on an exponential relationship with ambient operating
temperature and a linear relationship with operating voltage.

Is there a good source for determining the life of an Al Capacitor?
Does anyone know of a good white paper or similar? I would rather have
a more reliable source than a suppliers website or at least know that
the information is reliable enough.

Thanks,

Carlos

For ordinary commercial useage at or near rating voltage, i would say
the life expectancy would exceed 20 years.
I base this on the fact that i have seen numerous *wet* aluminum
electrolytics (like the ones used in the 20's and 30's) still fully
functional after 10 years of use, and a good percentage fully functional
after 20 years of use.
The "older" ones failed due to evaporation of the liquid; but
rejuvination was simple and quick via replacement of the "secret"
liquid.
Since aluminum electrlytics now do not use a liquid electrolyte, then
there is nothing to evaporate.

Keep in mind that this is based on ripple currents well within the
rating of the capaciror, as well as the temperature of its environment.
 
S

Spehro Pefhany

Jan 1, 1970
0
For ordinary commercial useage at or near rating voltage, i would say
the life expectancy would exceed 20 years.

The ratings are more like 2,000 *hours* at rated temperature (4%
failures).
I base this on the fact that i have seen numerous *wet* aluminum
electrolytics (like the ones used in the 20's and 30's) still fully
functional after 10 years of use, and a good percentage fully functional
after 20 years of use.
The "older" ones failed due to evaporation of the liquid; but
rejuvination was simple and quick via replacement of the "secret"
liquid.
Since aluminum electrlytics now do not use a liquid electrolyte, then
there is nothing to evaporate.

Keep in mind that this is based on ripple currents well within the
rating of the capaciror, as well as the temperature of its environment.

Best regards,
Spehro Pefhany
 
R

Roy McCammon

Jan 1, 1970
0
Obelix said:
I've been looking for a formula describing the life expectancy of Al
Electrolytic Capacitors. I found a couple of sources that descibe life
expectancy based on an exponential relationship with ambient operating
temperature and a linear relationship with operating voltage.

Is there a good source for determining the life of an Al Capacitor?
Does anyone know of a good white paper or similar? I would rather have
a more reliable source than a suppliers website or at least know that
the information is reliable enough.

http://www.vishay.com/docs/90017/reliabil.pdf
 
B

budgie

Jan 1, 1970
0
I've been looking for a formula describing the life expectancy of Al
Electrolytic Capacitors. I found a couple of sources that descibe life
expectancy based on an exponential relationship with ambient operating
temperature and a linear relationship with operating voltage.

Is there a good source for determining the life of an Al Capacitor?
Does anyone know of a good white paper or similar? I would rather have
a more reliable source than a suppliers website or at least know that
the information is reliable enough.

The humble elector is probably the electronic component with the least
consistent life expectancy across manufacturers, due mainly to their targetting
different intercepts on the cost/performance curve.. Look at what happened
recently with low voltage electros on PC motherboards, because someone with an
"imcomplete" formula offered cheaper products to cent-sensitive board makers.

Any time you see lifetime figures on a manufacturer's website for electros, it
will not be applicable to the next manufacturer. I wouldn't even expect to be
able to use the thermal expression from one on another's product.

The life expectancy is probably directly proportional to the price you pay.
 
R

Robert Baer

Jan 1, 1970
0
Spehro said:
The ratings are more like 2,000 *hours* at rated temperature (4%
failures).


Best regards,
Spehro Pefhany

Yes, there is a (ahem) slight discrepancy of the 2,000 hour rating and
the experience of seeing aluminum electrolytic capacitors operate for
more than ten years.
Granted that such caps used for 5 or so years and then equipment sit
on shelf or outside for another 5 or so years may need re-forming to be
used for another 5 or so years.
I am speaking of equipment like scopes and other test equipment made
by HP, Tektronix, EG&G etc back in the tube days (1960's or so)
retrieved from scrap dealers.
And they are still going strong...
 
A

Allan Herriman

Jan 1, 1970
0

That link is for caps with an organic semconductor dielectric, which
behave differently to the regular electros.

OS - Factor of 3.2 decrease in lifetime for each 10 degree increase in
temperature. (The datasheet may quote this as factor of 10 for each
10 degrees.)

Normal - Factor of 2 decrease in lifetime for each 10 degree increase
in temperature.


If the temperature isn't too high, the organic semiconductor ones may
have huge (expected) lifetimes.
They will also have lower ESRs, which results in lower self heating
(which also helps the lifetime), although in my experience, nearby
semiconductors have more of an effect on the temperature than anything
else.

Regards,
Allan.
 
R

R.Legg

Jan 1, 1970
0
Any time you see lifetime figures on a manufacturer's website for electros, it
will not be applicable to the next manufacturer. I wouldn't even expect to be
able to use the thermal expression from one on another's product.
If a manufacturer doesn't publish their own data, beware.
The life expectancy is probably directly proportional to the price you pay.

This would be a very simple way of improving component quality, if it were true.
Why don't you patent it?

RL
 
R

Roy McCammon

Jan 1, 1970
0
Allan said:
That link is for caps with an organic semconductor dielectric, which
behave differently to the regular electros.

yup. I figure the OP can do his own fishing if I show him
the pond.
 
Y

Yzordderex

Jan 1, 1970
0
[email protected] (R.Legg) wrote in message

snip---

Heheh. Must be the most difficult question to answer or calculation
to perform. I for one would like to hear what your application is.

In a nutshell it boils down to hottest temperature inside of cap. Not
as difficult to predict if load and conditions are known.

case 1 - Set top box for cable tv receiver. Ambient temperature is
25c, load is well defined, and can assume some duty cycle. On at 6am,
off at midnight if you wish. Line impedance is reasonablty well
defined as most residential installations closer to 10kVA than 100kVA.

case 2 - 3 phase AC motor speed control bus caps. Ambient temperature
0-50c, load unknown, duty cycle unknown, phase imbalance unknown, line
impedance unknown...yada yada yada..

If case one then you measure inner capacitor temperature (or outer if
you can then calculate inner temp from that) and use this to predict
lifetime. Can also get frequency spectrum of current waveform and
apply each harmonic to esr at that harmonic to figure out power
dissapated. That and can geometry will tell you internal temperature
and then get lifetime from there.

If case two then it's basically pull a number out of your ass. In
other words experience will be your guide. To attempt an analytical
approach to case two would be an excerise in futility.

Hope this helps. Again, what is application?

regards,
Bob
 
F

Frithiof Andreas Jensen

Jan 1, 1970
0
"Robert Baer" <[email protected]> skrev i en meddelelse

I am speaking of equipment like scopes and other test equipment made
by HP, Tektronix, EG&G etc back in the tube days (1960's or so)
retrieved from scrap dealers.
And they are still going strong...

Ususally, the 2000 Hours rating, which is typical, is at 80 degrees Celcius
core temperature of the capacitor and at rated ripple load.

Decreasing the core temperature will cause the life expectancy to grow
exponentially - *how* exponentially is disclosed in the manufacturers
datasheets, there are curves in there. Below 30 degrees Celcius, the
lifetime can well be a decade or so at rated load.

When we add a Gaussian distribution to the probability of failure, several
decades for some capacitors in a given sample is probable.

But, since we wouldn't like to rely on chance when going to Mars, we use the
Manufacturers Datasheets instead of anecdotal evidence ;-)
 
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