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Suppose I have a device that utilizes a supercapacitor.

How long will it take to wear out the supercapacitor so that it needs replacement?

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Overview

In general capacitor lifetime (including supercapacitors) is dependent on three things:

  1. Electrolyte Life
  2. Voltage Derating
  3. Temperature / Power Dissipation

If you want the capacitor to last a long time, limit the applied voltage, keep it cool, and limit the output current. All this should be in the datasheet of your capacitor.

Electrolyte Life

If the capacitor is, say, ceramic or tantalum, the electrolyte is a solid and the cap will basically never go bad. If it's an electrolytic, then it contains fluid which will evaporate and eventually cause the cap to fail. In an electrolytic double-layer super-capacitor, the electrolyte is a combination of a fluid and of activated carbon, so it is mildly vulnerable to evaporation.

Voltage Derating

More important, though, is the voltage derating of the capacitor. If the voltage burns the cap up on the first use, you won't need to worry about evaporation. A capacitor is a carefully constructed device which separates two conductive films with a thin, thin layer of insulating material over a wide area (folded or rolled into a package). Decrease the separation, and you've got higher capacitance with the same area. This thin separation is vulnerable to high voltages; that's why capacitors have specific voltage maximums, often printed on the case. In a supercap, this barrier is often just nanometers thick, and the dielectric will not insulate high voltages across this short distance.

Using a cap at close to its maximum voltage will cause it to fail more quickly than using it at a lower voltage, this tradeoff is known as a derating curve. It should be available from your capacitor manufacturer.

Temperature / Power Dissipation

A capacitor is negatively affected by heat. It causes the electrolyte to evaporate more quickly, causes the dielectric to be weakened, and it can damage the thin conducting elements in the capacitor. Both environmental heat and self-heating effects should be considered. If the capacitor is discharged very rapidly, the small resistance of the foil and leads will be inconsequential compared to the square of the current.

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  • \$\begingroup\$ That's all good, but may I have any quotes on how long it can last under some reasonable conditions? Like "15 to 20 years if you do it right and up to one year if you severely abuse it"? \$\endgroup\$ – sharptooth Feb 9 '12 at 8:51
  • \$\begingroup\$ Thousands of years if you store it in an airtight vault and don't use it, milliseconds if you connect it to a high-voltage power line on the surface of the sun. I'm guessing you want to use them to power a car, you'll have to run the numbers for that with your specified capacitors, quantity in series and in parallel, motor draw, operating temperature, etc. \$\endgroup\$ – Kevin Vermeer Feb 9 '12 at 8:59
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Every capacitor has different characteristics. You should check out the datasheet of you capacitor to figure out when it needs replacement.

The characteristics of your capacitor will change over time, under certain conditions. Usually, (super)capacitors have a parameter called endurance / load life (in hours) or life cycles (in cycles). An example of what you can find in a datasheet:

After 1000 hours application of 5.5V DC at +85°C, the capacitor shall meet the following limits:

  • Capacitance change: ±30% of initial measured value

  • Internal resistance: < 4 times of initial specified value

So, in the case above, you can decide if a change of ±30% of the initial capacitance is still suitable for your application. If not, you should replace the capacitor after 1000 hours of operation under those conditions.

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An extremely good reference here

http://www.digikey.co.nz/Web%20Export/Supplier%20Content/CooperBussmann_283/PDF/CooperBussmann_Guidelines_using_aerogel.pdf?redirected=1

Which includes the comment:

  • PowerStor supercapacitors have a longer lifetime than secondary batteries, but their lifetime is not infinite. The basic end-of-life failure mode for a supercapacitor is an increase in equivalent series resistance (ESR) and/or a decrease in capacitance. The actual end-of-life criteria are dependent on the application requirements. Prolonged exposure to elevated temperatures, high applied voltage and excessive current will lead to increased ESR and decreased capacitance. Reducing these parameters will lengthen the lifetime of a supercapacitor. In general, cylindrical supercapacitors have a similar construction to electrolytic capacitors, having a liquid electrolyte inside an aluminum can sealed with a rubber bung. Over many years, the supercapacitor will dry out, similar to an electrolytic capacitor, causing high ESR and eventually end-of-life.

Here is a diagram from the above reference which puts some figures on various effects. enter image description here

The 'key' does not make full sense. The significant effect of voltage on lifetime is worth noting.


This reference is about supercap aging - not immediately apparent.
Appears to be the middle of a wider discussion.
Worthwhile.


Some related discussion here

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