6 ms·

If you want your aluminum capacitors to fail less often: - If you are designing the PCB and not repairing, keep them as far away from heat sources as possible.

by laydn 8y ago

If you want your aluminum capacitors to fail less often: - If you are designing the PCB and not repairing, keep them as far away from heat sources as possible. If you're repairing a PCB and the caps are near heat sources, consider isolating them with thermal material - Use the highest temperature rating capacitor that you can find, if cost is not a concern. - Most caps now have a lifetime rating such as (4000 hrs in 85C). This lifetime also has built-in ripple current assumptions, but for a first order approximation, consider using the "longest rated at highest temperature" cap, if cost is not a concern. - Again, as a very rough guideline, use the highest voltage rated capacitor that you can find for your target rail. This is an approximation, because your second goal should be to generally keep the ESR (equivalent series resistance) low, and as the voltage rating increases, so does ESR. Commercial products tend to choose the voltage rating around 1.2x - 1.5x target voltage. Most industrial products that I've seen target a minimum of 2x.

sokoloff 8y ago
> use the highest voltage rated capacitor that you can find for your target rail I think you meant to say lowest (or you have some other sign negation in that section, or I misunderstand something)
- laydn 8y ago
  No, I meant highest. For example: If your target rail is 12V, use a minimum of 16V rated capacitor, but prefer a 25V rated capacitor over 16V. This application note has a very detailed explanation of Aluminum capacitor reliability (page 12): http://www.cde.com/resources/catalogs/AEappGUIDE.pdf http://www.cde.com/resources/catalogs/AEappGUIDE.pdf
  - sokoloff 8y ago
    Thanks. I misread the increase in ESR as a governing effect, rather than a secondary effect.
- deelowe 8y ago
  Nope, higher. Voltage and heat kills electronics. The better the rating, the longer the reliability.
wang_li 8y ago
>consider isolating them with thermal material This only slows down the transfer of heat, both in and out. I'd be surprised if anything useful would come of this as eventually the cap is going to achieve equilibrium with the environment, or if you wrap it up in a small coat, it will take longer to transfer heat out of the cap than normal and run hot.
- city41 8y ago
  I thought OP meant use thermal material while doing the repair, such as when using heat guns or soldering irons.
- robocat 8y ago
  Think a linear wall of isolation, so the capacitor can still dissipate heat to the air. A jacket around the capacitor would be a bad idea, especially since capacitors can generate heat internally, and heat is what we don't want!
  - magicalhippo 8y ago
    Their lifetime is also non-linear with respect to ambient temperature. A 10 C reduction[1] in ambient temperature roughly doubles the lifetime. So shielding the capacitor from heat can be very beneficial, even if it's just a few degrees. [1]: www.rubycon.co.jp/en/products/alumi/pdf/life.pdf
- syrrim 8y ago
  >eventually the cap is going to achieve equilibrium with the environment the environment is probably around 25 degrees. It's sitting between the environment and some heat producing element, so it will reach steady state somewhere between 25 degrees and the temp of that element. Making it as far away (thermally) as you can from that element should lower it's steady state temperature.
robocat 8y ago
Adding detail about your ESR sentence: use the highest voltage capacitor if it is a low frequency use (e.g. 100Hz). For high frequency use you also must have a good ESR rating - here's the part from the article about that: "On the other hand, electrolytic capacitors used in switch-mode power supplies (SMPS) operate at very high frequencies and take considerable amounts of ripple current. Every capacitor has an intrinsic loss, and this is often expressed as an ESR. Power dissipated in a capacitor can be expressed as I^2*R, where I is the ripple current in Amps RMS, and R is the ESR. With higher ripple currents, the loss in the capacitor itself can become significant, and cause self heating of the capacitor. For use in SMPS, special low-ESR capacitor types have become popular in the past few decades to reduce this loss and allow capacitors to take more ripple current without shortening the life of the capacitor. However, many of the cheaper brands of caps, most notably those coming from east asian manufacturers, have historically had problems in this regard. There was a period in the late 90’s to early 2000’s known as the capacitor ‘plague’ where many manufacturers went with cheap low ESR capacitors from these manufacturers, only to find many power supplies were failing prematurely (within a year or two of manufacture)."

by laydn 8y ago

sokoloff 8y ago

> use the highest voltage rated capacitor that you can find for your target rail I think you meant to say lowest (or you have some other sign negation in that section, or I misunderstand something)

laydn 8y ago
No, I meant highest. For example: If your target rail is 12V, use a minimum of 16V rated capacitor, but prefer a 25V rated capacitor over 16V. This application note has a very detailed explanation of Aluminum capacitor reliability (page 12): http://www.cde.com/resources/catalogs/AEappGUIDE.pdf http://www.cde.com/resources/catalogs/AEappGUIDE.pdf
- sokoloff 8y ago
  Thanks. I misread the increase in ESR as a governing effect, rather than a secondary effect.
deelowe 8y ago
Nope, higher. Voltage and heat kills electronics. The better the rating, the longer the reliability.

wang_li 8y ago

>consider isolating them with thermal material This only slows down the transfer of heat, both in and out. I'd be surprised if anything useful would come of this as eventually the cap is going to achieve equilibrium with the environment, or if you wrap it up in a small coat, it will take longer to transfer heat out of the cap than normal and run hot.

city41 8y ago
I thought OP meant use thermal material while doing the repair, such as when using heat guns or soldering irons.
robocat 8y ago
Think a linear wall of isolation, so the capacitor can still dissipate heat to the air. A jacket around the capacitor would be a bad idea, especially since capacitors can generate heat internally, and heat is what we don't want!
- magicalhippo 8y ago
  Their lifetime is also non-linear with respect to ambient temperature. A 10 C reduction[1] in ambient temperature roughly doubles the lifetime. So shielding the capacitor from heat can be very beneficial, even if it's just a few degrees. [1]: www.rubycon.co.jp/en/products/alumi/pdf/life.pdf
syrrim 8y ago
>eventually the cap is going to achieve equilibrium with the environment the environment is probably around 25 degrees. It's sitting between the environment and some heat producing element, so it will reach steady state somewhere between 25 degrees and the temp of that element. Making it as far away (thermally) as you can from that element should lower it's steady state temperature.

robocat 8y ago

Adding detail about your ESR sentence: use the highest voltage capacitor if it is a low frequency use (e.g. 100Hz). For high frequency use you also must have a good ESR rating - here's the part from the article about that: "On the other hand, electrolytic capacitors used in switch-mode power supplies (SMPS) operate at very high frequencies and take considerable amounts of ripple current. Every capacitor has an intrinsic loss, and this is often expressed as an ESR. Power dissipated in a capacitor can be expressed as I^2*R, where I is the ripple current in Amps RMS, and R is the ESR. With higher ripple currents, the loss in the capacitor itself can become significant, and cause self heating of the capacitor. For use in SMPS, special low-ESR capacitor types have become popular in the past few decades to reduce this loss and allow capacitors to take more ripple current without shortening the life of the capacitor. However, many of the cheaper brands of caps, most notably those coming from east asian manufacturers, have historically had problems in this regard. There was a period in the late 90’s to early 2000’s known as the capacitor ‘plague’ where many manufacturers went with cheap low ESR capacitors from these manufacturers, only to find many power supplies were failing prematurely (within a year or two of manufacture)."