Thoughts and questions about electrolytic capacitors lifetime

[kraal]

Hi,

While cross checking the capacitors I selected for one of my projects, I realized that I selected some having a lifespan of only 2000 hours. This triggered many questions.

A quick calculation shows that if a standard "casual playing session" is 1 hour, the lifetime of the pedal  in which the 2000 hours capacitor is used is 2000 playing sessions (less than 6 years of daily playing)... but this is true if and only if the owner never forgets to turn off the power supply. 2000 hours is only ~83 days always on (less than 3 months)

Using 5000 hours caps brings the lifespan to a total of ~210 "always on" days. The longest lifetime I found for a 100uF is 26000 hours which represents 3 years "always on" (leaded caps, smd ones seem to have shorter lifetime).

One year ago I tinkered with an on/off switch on my pedalboard in order to make sure to not forget to unplug it from the wall. However I'm pretty sure that many people leave the PS always plugged in at home and leave the pedals in bypass mode not thinking that if slowly kills their beloved devices.

So here are my questions:

• Am I missing something (I mean, I almost never completely turn off my TV, it's always in standby and is 7 years old, my home server is 7 years old as well and stays on 24/7, my parents' HiFi is almost 40 y.o. and used daily for hours) ?
• how do you deal with this issue in your project (should I even care about it) ?
• How do you select your capacitors (from a lifetime perspective, i.e. what lifetime do you usually select) ?

Thanks in advance !

[11-90-an]

as far as I remember the lifetime of the caps specified also relies on how much volts it's exposed to, i.e. 2000 hrs for 15v, or something like that...

check the datasheets... since you would probably  be running most of them on 9v or less, the expected lifetime will be "longer" than expected.

[EBK]

....
Am I missing something?

Yes. 
The lifespan of electrolytic caps is specified as hours if operated at their rated voltage, maximum temperature rating and with maximum ripple current applied to the capacitor. Changing any of those factors dramatically increases the lifespan, and under realistic operating conditions, we don't get close to those extremes anyway.

[composition4]

A couple of points...

- A 25v 2000h rated electrolytic will last a lot longer than 2000h at 9v. Search google for "derating electrolytic capacitors" for more info. It's all tied in with ESR/temperature/ripple.
- It also depends on the definition of "life" of the cap. 2000h might mean "After 2000h the capacitance will be 20% less" or "The ESR will be double". In both cases, that may be fine in your design well after the manufacturer's definition of end of life, i.e. if you are using the cap as a power supply filter and you've overengineered the capacitance you needed from the start.

Usually it's not that critical, for the low voltages we work with in pedals, just choose a cap rated at double to a few times the operating voltage and it'll last as long as you will ever need. Obviously size and cost can be a factor, but you can allow for it in your design!


Edit: yeah, what those two above me said more concisely!

[kraal]

Thank you for your crystal clear replies ^^

[amptramp]

If you want accurate derating for every type of component as determined by test and evaluation and used in military design, download this:

https://elsmar.com/pdf_files/Military%20Standards/MIL-HDBK%20217F.pdf

"Reliability Prediction of Electronic Equipment"

You plug in values for quality, temperature, stress ((DC + AC peak)/rated V), environment, series resistance into equations that give you a failure rate in failures per million hours.  It's simpler than it sounds and it lets you know the effect of changes in these parameters.  Take the value of failures per million hours, divide by a million and take the reciprocal and that is the component lifespan in hours.

[Rob Strand]

The 2000hr rating is at the rated temperature.  A typical temperature rating is 85C.

For a pedal which doesn't get hot you are operating at 25C, so you are 60C under the rating.

A very crude rule of thumb is lifetime doubles (or halves for hotter) for each 10C.

The 60C means reduction means a factor of 2^6  increase in lifetime.
That's 128000 hrs, which is about 15 years.

If you use 105C rated caps the you get more increase than the 85C caps; another factor of 4 making, it 60 years.

(You can add on the derating stuff amptramp mentioned as well.)

On top of that is what does the 2000hr figure mean 


One thing I forgot to mention is Electrolytic caps sitting on the shelf are using up their life, the life clock doesn't stop when you turn off the equipment.  In fact not using electrolytics can shorten the life.  For example,

https://passive-components.eu/get-the-lowdown-on-shelf-life-and-storage-of-capacitors/