18
\$\begingroup\$

Many motherboard manufacturers use "Low ESR Solid Organic Polymer" capacitors instead of electrolytic caps and put great effort into marketing and advertising this fact. (For example, this FAQ by Giga-Byte.)

In addition to "lifespan" do these type of capacitors have other advantages such as greater tolerance for out-of-spec voltages or temperatures?

Do these capacitors have a significant advantage over electrolytics? If so, is it advisable to use them instead in hobby projects?

\$\endgroup\$

2 Answers 2

16
\$\begingroup\$

Organic polymer capacitors, also known by names like OC-CON and trademarks like OSCON, give you a bit better performance than the best low-ripple aluminum electrolytic (ALE) capacitors at a higher cost, with a few caveats.

Ripple current for an OC-CON is generally higher than an ALE of equivalent size and rating. Good ALEs in the 1000 µF, 16 V range can have 100 kHz ripple ratings around 1500 mA - OC-CONs in the 820 µF, 16 V range can be as high at 5600 mA.

OC-CONs are generally not as forgiving in terms of overvoltage as ALEs are. I've found that overvoltage will cause an OC-CON to fail short-circuit. ALEs seem to be able to take more overvoltage before failing.

OC-CONs also need to have charging current within a controlled range. Excessive charging current can degrade the leakage current performance or cause a short.

In terms of life, there are ALEs available with 8000 h rated life, so there's no guarantee that every OC-CON will have longer rated life than any ALE. There are ranges for both. That being said, there likely aren't any 'general-purpose' OC-CONs with only 1000 h rated life out there.

Sanyo has published this usage guide for their OSCON capacitors - the principles hold true for any OC-CON part in my experience (most manufacturers have similar documents).

For hobby use, you may be better-served by ALEs, since they're a bit more robust and cheaper. If you need the high ripple capability, however, there's nothing stopping you from using them - just be careful soldering them (see section 3 of the linked document). I haven't had any issues hand-soldering them, FWIW...

\$\endgroup\$
10
\$\begingroup\$

Yes, solid polymer capacitors will generally have a longer lifetime than wet electrolytic Aluminum capacitors (WEACs for now :-)).

The exceptions are special cases. The main lifetime degradation mechanism of WEACs is electrolytic dry out. When other factors are held constant, lifetimes are reasonably well described by the recently discussed expression

Life =~~ rated life x 2^((Trated-Twkg)/10)

ie lifetime doubles for every 10 degrees C below rated temperature.

Trated is usually 85C for consumer use and 105C for more severe (if not perhaps 'professional' use).

Rated life is usually 2000 hours, may be 1000 hours, and is usually a multiple of 1000 hours or perhaps 500 hours. You can buy 3000 hour or even 5000 hour caops BUT expect to pay. This coarse granularity reflects the inexact nature of the real life figure.

What this means is that WEACs tend to be easy to shorten the life of when things get hot or when internal heating occurs.

"Solid Organic polymer" caps do not share this main lifetime failure mechanism. Manufacturers rated lifetimes are typically 5 to 20 times longer, as gigabyte show.

If a 125 C 6000 hour WEACs was obtained it would notionally have an extended lifetime over a 2000 hour cap of a factor of 2^((125-105)/10)) x 6000/2000 = 12 times. This is > the 5 x improvement of some solid polymer caps BUT a very unusual and VERY high spec part. As polymer caps generally improve they will tend to be better than all but the very very very best WEACs. Expect to pay for it :-)

http://www.kemet.com/kemet/web/homepage/kechome.nsf/WebEn/KO%20Conductive%20Polymer)

http://www.kemet.com/kemet/web/homepage/kechome.nsf/WebEn/T520%20KO-CAP

http://www.kemet.com/kemet/web/homepage/kechome.nsf/vapubfiles/T520BTechUpdate/$file/T520BTechUpdate.pdf

http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/T520%20Series/$file/KEM_T2015_T520.pdf

http://www.kemet.com/kemet/web/homepage/kechome.nsf/WebEn/T525%20KO-CAP

http://www.kemet.com/kemet/web/homepage/kechome.nsf/WebEn/T525faq

http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/T525%20Series/$file/KEM_T2017_T525.pdf


Lifetime doubling per 10 degrees C decrease in operating temperature:

The doubling of operating lifetime per 10 degrees Celsius decrease in operating temperature is based on the Arrhenius equation which describes the change in reaction rates with temperature.

A web search on life of electrolytic capacitors provides many related links.

A few related references:

Capacitor life calulators - note the 2^x term for aluminum electrolytics where x is related to delta-temperature/1-.

Calculating the Lifespan of Electrolytic Capacitors with De-Rating

Aluminum Electrolytic Capacitors Life expectancy

Power Tip 50: Avoid these common aluminum electrolytic capacitor pitfalls - see 1st 'tip'

Wikipedia - capacitor lifetime and notes 93 94 95

Determining end-of-life, ESR, and lifetime calculations for electrolytic capacitors at higher temperatures

\$\endgroup\$
3
  • \$\begingroup\$ Where did you see the part about how the lifetime of the cap doubles as operating temperature lowers ? \$\endgroup\$
    – VanGo
    Sep 7, 2017 at 13:25
  • 1
    \$\begingroup\$ @VanGo Arrhenius equation - see addition at end of answer. \$\endgroup\$
    – Russell McMahon
    Sep 11, 2017 at 18:34
  • 1
    \$\begingroup\$ Somewhat outdated, reasonably enough considering the age. 5000hr elcaps are not especially expensive and lifetime @ 105C is typically specified. Rubycon 1mF 16V 1.2A 6000hr@105C can costs 10p for example. With the current drought of MLCCs, designers are forced to look at cans again for SMPS parts. Poscons seem to depend a lot on manufacturer. United Chemi Con claims 15k hours (!) while other manufacturers cap at 5k hours. \$\endgroup\$
    – Barleyman
    Nov 23, 2018 at 14:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.