capacitor type longevity need some input.. what types last the longest? - Page 1
Forum section: electronics / projects

author: jeffd1988
author_rank: Newbie
timestamp: May 13, 2018, 01:00:43 am
content: I'm doing a project were i want it to last as long as possible i tried to do some research on capacitors and could not fined much about it. all i was able to find out is that electrolytic capacitor can't sit for long periods of time or they can short out or something and that you can slowly charge them back up to get then to work again and they can also dry out so i'm thinking that a Aluminum Organic Polymer Capacitor would be a good replacement also that ceramic capacitor could short so putting two in series with each other can help prevent failure.basically i'm asking if any one has some advice on this or some link to share or somethingi'm planing on using ceramic capacitor for by-passing for mcu's and some low power out put filter on boost converter with about 1 amp output that will mostly be un-powered or powered with no load

author: MosherIV
author_rank: Super Contributor
timestamp: May 13, 2018, 10:09:28 am
content: HiMost ceramic and foil types last a long long time.The exception are "rifa" foil caps. They are encapsulated in plastic but the plastic goes hard and cracks over time. When the plastic cracks, moisture gets in and shorts the plates and they blow up when powered up. They tend to be used as mains input filter caps, they smell like burning paper (I think the seperator is paper)Tantalum capacitors have a shelf life. After 10 to 15 years they go bad and tend to blow up when power up.Electrolitics do have a shelf life. I volunteer at a computer museum and we have powered up 35year old computers with no problems with the caps. Beyond the 35 year threshold, we have to check out the caps. This is probably the effect that you describe. They can be 'reformed' by slowly bringing up voltage on them but one of my colleagues at the museum tells me that it takes a long time and the cap never really recovers to the same as before so it is easier to replace the cap.In the past 10 years, there has been a perceived degredation in life of electrolitic caps. They are 2 issues with electrolitic caps:1. Temperature - heating them up will cook the electrolite. So try to keep them away from heat sources. Even if they have a high temp rating, cooking them will ALWAY boil off the electrolite.2. Ripple current - most caps in PSUs go bad because they have chosen cheaper caps that cannot stand the high ripple current in SMPS type supplies. Cost, size (and sometime ignorance) temds to lead designeds/producers to choose caps that cannot stand the ripple current and fail within a few years.

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: May 13, 2018, 10:18:58 am
content: After testing many used capacitors on my Eico 950, the ones that seem the best are the Nichicons. The Rubycons not so much. Of course you need to take into consideration how much wear an tear these things have seen over the years. Hope this helps.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 13, 2018, 10:33:18 am
content: Any experience with Panasonic elcaps?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 13, 2018, 07:01:09 pm
content: How long is a long time? Electrolytics can go for 50 years or more if properly chosen and properly applied. What you can't anticipate is some production problem with a given batch that cuts the life short. Derate them and run them cool- heat is the enemy. Buy the long life solvent resistant versions in 105C if you can.Tantalums have a bad reputation for shorting out. Once it's happened to you, you'll be wary forever. Actually, if you follow the application notes to the letter, they rarely fail. They have to be derated. Current spikes have to be avoided. The slightest reverse voltage has to be avoided. You never use them in a circuit where current isn't limited- just in case they still short out! I use them in equipment I never want to service again, but I choose them with great care. The military uses/used a lot of wet slug tantalums. They're also very reliable, but the cost of new ones is a bit insane.MLCCs are reliable, but be very careful of board flex. If they crack, and it does happen, all bets are off.IMO, good dipped or boxed films last nearly forever, save for known problem children, but they just don't fit in all applications.If you test caps for value, losses and DC leakage before installation, you'll weed out the rare weak ones. I've been buying caps for 40+ years and I don't think I've ever gotten a bad one NIB.

author: bd139
author_rank: Super Contributor
timestamp: May 13, 2018, 08:38:27 pm
content: Nothing lasts forever. Design it to be replaced well inside the worst MTBF chosen from a cost analysis and you’re sorted.Unless it’s going to the stars.

author: David Hess
author_rank: Super Contributor
timestamp: May 13, 2018, 11:29:07 pm
content: Aluminum electrolytic, aluminum polymer, and tantalum polymer capacitors wear out just sitting there but operating life in excess of 20 or even 40 years is possible if properly derated. The wet electrolyte in aluminum electrolytic capacitors evaporates over time and the polymer in aluminum polymer and tantalum polymer capacitors degrades. Operating life however is application dependent; maybe you do not care if the capacitance has dropped 20% and the ESR has doubled.Solid tantalum capacitors have no wear out mechanism (1) but need to be derated and applied correctly for the desired reliability. Dry solid tantalum capacitors in axial leaded metal packages like the Kemet T110 series avoid the strain induced failures of plastic packaged parts but are pretty expensive. The similarly packaged wet tantalum capacitors eventually have problems with corrosion.Ceramic and film capacitors do not wear out with some exceptions like MosherIV mentioned but over the long term, I have had better reliability with plastic film capacitors and they work fine in decoupling applications.(1) A NASA article on the subject mentions "field crystallization" around defects but only in high voltage solid tantalum capacitors. I do not know how seriously to take this and self healing should handle it if the part was derated properly.

author: jeffd1988
author_rank: Newbie
timestamp: May 14, 2018, 06:34:20 am
content: thanks this was what i was looking forlower capacitance and high ESR is fine in my application Nichicons is one of the output caps that i was looking at but the problem is board flex and the MLCC there is a battery pack install right on to the side of the board if it was ever dropped this could make the board flex made be some foam between the two would salve this problemalso i use low temp solder past so i don't think i have to worry about damaging them with heat so much it melts at 137c

author: Jwillis
author_rank: Super Contributor
timestamp: May 14, 2018, 08:42:39 am
content: The soldering heat really isn't a problem as long as it's not prolonged heating .Here's some good reading material for Aluminum Electrolytic Capacitors.It has a section on Reliability and Lifetime .Interesting stuff.http://www.cde.com/resources/catalogs/AEappGUIDE.pdf

author: xani
author_rank: Frequent Contributor
timestamp: May 14, 2018, 11:51:45 am
content: Nichicon havehandycalculator for lifetime

author: KhronX
author_rank: Frequent Contributor
timestamp: May 14, 2018, 12:10:55 pm
content: That is, Rifametalized papercaps, the transparent-resin-potted ones (andnotALL of their foil caps, afaik).https://i.ebayimg.com/images/i/181607500792-0-1/s-l1000.jpghttps://4.bp.blogspot.com/-5mzf_Ws3Yrk/VwpbHyWTPDI/AAAAAAAAETk/QurGR_fSkZwgApL4xC5PgfpFVrODxDlOQ/s1600/Dead%2BRIFA%2Bcap.jpgQuote from: MosherIV on May 13, 2018, 10:09:28 am

author: Mr. Scram
author_rank: Super Contributor
timestamp: May 14, 2018, 12:40:54 pm
content: Quote from: xani on May 14, 2018, 11:51:45 amIt's fairly annoying you have to pick a specific series first, rather than having it show you what's most likely to last longest based on your requirements.

author: David Hess
author_rank: Super Contributor
timestamp: May 14, 2018, 01:11:01 pm
content: Quote from: jeffd1988 on May 14, 2018, 06:34:20 amStart with the long life specified parts and the higher temperature specified parts. Then use a physically larger capacitor, higher voltage and higher capacitance, than necessary because it will have more electrolyte and take longer to dry out.QuoteIt helps to use smaller surface mount parts and to align them so that their shortest dimension is at a right angle to the direction of flexing. Slots can also be cut for strain relief to direct bending away from specific areas.Some surface mount parts have mechanically compliant terminations which allow them to flex without breaking.

author: jeffd1988
author_rank: Newbie
timestamp: May 14, 2018, 06:45:09 pm
content: Quote from: David Hess on May 14, 2018, 01:11:01 pmok so go with thishttps://www.mouser.com/ProductDetail/647-RNS1D101MDN1PHinstead of thishttps://www.mouser.com/ProductDetail/647-RNS1D150MDS1JTwhich got 15 years and that is the max that the calculator will goso there is extra head room its also only about twice as much and wont effect the BOM much and also not use the 1206 smd but 805 or should it be more like 603 but 603 might be to low in mW the flex would be in the area of 1mm per 60mm probably but i think i can get that down to a 10th of that or so

author: David Hess
author_rank: Super Contributor
timestamp: May 14, 2018, 08:25:38 pm
content: Quote from: jeffd1988 on May 14, 2018, 06:45:09 pmOr make sure to mount the 1206's perpendicular to the direction of flexing.If this is suppose to be a high reliability assembly, then consider a better substrate than FR4.

author: jeffd1988
author_rank: Newbie
timestamp: May 15, 2018, 12:47:57 am
content: Quote from: David Hess on May 14, 2018, 08:25:38 pmso like aluminum substrate??

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2018, 02:17:09 am
content: Quote from: jeffd1988 on May 15, 2018, 12:47:57 amHybrids were often built on something like alumina. I have also seen a lot of automotive assemblies built on something similar.

author: Mr. Scram
author_rank: Super Contributor
timestamp: May 15, 2018, 07:01:07 am
content: What kind of high reliability are we talking about? Longevity, temperature, vibration, shock?