Every capacitor has a temperature and lifetime rating. The
technology family also has different scale factors for the
Arrhenius equation (i.e. different activation energy Ea).
Arrhenius is used, because curve fitting the equation
against the lifetime of capacitors, tends to correlate well,
and suggests a chemical reaction nature to the failures.
(Higher operating temp, means failure sooner.)
http://en.wikipedia.org/wiki/Arrhenius_equation
Foe example, one capacitor product might be rated for
3000 hours at 105C. That doesn't mean we runs the
capacitors at 105C. Maybe they run at 45C for example.
That is 60C below the rating. Maybe the cap is running
about 10C above the temperature of the air in the
computer case, about 35C. Caps will be a little warmer
than their surroundings, at least on something like
the Vcore circuit.
The scale factor, might be a doubling of life for every
10C drop in temperature. Another product family might
have a doubling of life for every 15C drop in temperature.
Say we use the latter factor. The 60C difference in the
actual application temperature, results in 2**4 or a
16 times improvement in life. That means the
number of hours jumps to 3000*16 or about 5.5 years.
And that would be the mean time between failures.
So, to compare a solid electrolyte capacitor, to a
wet electrolyte capacitor, we need the "single point"
rating (what might be printed on the sleeve), plus some
knowledge of the curve-fitted Arrhenius equation.
(That usually comes from an application note on the
manufacturers web site.) Both capacitors will have to
be re-rated for the application temperature (which may
differ between the two devices as well). If one cap has
a different ESR/ESL, fewer or more caps are required and
so on, that can change the operating temperature rise above
ambient. So they both won't be running at 45C, as one
cap may be under more stress in its design, than the
other.
Speaking in general terms, the solid electrolyte
caps are better than the wet electrolyte ones. But
if a wet electrolyte one is properly designed
(doesn't contain any of that pirated-formula
bad electrolyte), can it also do the job ?
Sure, a ten year life from an electrolytic isn't
unheard of. One web page I read, stated the rubber
seals fail after about 15 years, so it is possible
for them to last a while. When the seal fails, the
cap tends to eventually dry out.
http://en.wikipedia.org/wiki/Capacitor_plague
(By the way, my Antec power supply failed recently,
and looks similar to the picture in that article. You
can see four caps with the plague here.)
http://en.wikipedia.org/wiki/Image:PSU_Caps.jpg
So if you think the motherboard will be used continuously
for the next ten years, maybe the solid ones are a better
choice. The new board I bought with wet electrolytics
on it, isn't particularly concerning me. I upgrade
often enough, that a machine only sees daily use
for three years or so. My machine from 1999 still
works and boots fine.
Paul
