Why not seal super capacitors?

[Cliff Matthews]

Meh, no real loss, just one drawer full of old but unique history. Hope there was no PCB's inside, since I didn't use gloves while sawing it open..

[wraper]

Meh, no real loss, just one drawer full of old but unique history. Hope there was no PCB's inside, since I didn't use gloves while sawing it open..

You could check a datasheet if you can find one. Sometimes electrolytic capacitors may have something like +80/-20% tolerance instead of usual +/-20%. I personally would not use 30+ years old capacitors regardless of how good they are, though.

[perieanuo]

Best you can do is put resin, is what we did in manufacturing motor control boards, laser diodes and medical equipment. Which resin, that's other discussion... I think here people referred as glass resin compound (I used a compound with 1:6 ratio, black resin with transparent hardener). 24 hours for drying. Good solution but not cheap or easy to do with mixed components and some connectors...

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[SeanB]

Resin sealed caps do degrade with time and temperature cycling, the resin is not totally vapour proof, and the liquid ( and more importantly the hydrogen gas generated internally as the capacitor reforms) does diffuse through it and it slowly degrades. The only capacitors with a indefinite life are the wet solder sealed glass frit insulated tantalum types, as used in the Voyager spacecraft. Those are truly hermetic, as there is literally zero outgassing from them in a bare non sleeved case, and they will last decades in operation at 125C. Electrolyte in them is sulphuric acid, and the inside is silver plated steel or tantalum only, with a PTFE inner support structure.

The rectangular sealed capacitor referred to from Digikey I will tell you a nasty secret about some of them, they are internally just regular axial electrolytics with rubber seals, simply with a PCB each end that commons a few capacitors to make the final value, and then they are potted with a flexible encapsulant and an outer insulation sleeve to keep the terminals and board insulated from the case, and the leadouts are 2 short PTFE coated wires that are soldered to the inside of the terminals, and then the outer seal is low melting point solder for final seal after crimping the top on. They do not leak in use externally, but do lose vapour from the internal capacitor units into the housing, so they do fail by going high ESR and eventually nearly open circuit, but do not outgas at all from the case. Bloody expensive as well, and they were a pain, as the lead time was so long to get them. however those MSLH ones are slightly different in that they just take the rolled foil pack and flatten it ( so no lost mandrel construction like a regular electrolytic, these need a removeable mander in manufacture, a hand process to remove) then stuff it in a can, and laser or TIG weld it in a CA enclosure, and then use a vacuum fill to get the electrolyte in there, with a welded on fill port that is also a pressure vent ( weak point in the case for emergency vent). Will still have an operating life limit from degradation of the electrolyte with time and reforming though.

[Paul Moir]

Epoxy normally has a fairly lousy MVTR.  Not surprising a rubber, which likely also has a barrier layer added somewhere, can beat it.

[Raj]

better seal,would cause heating issues too.Why not create a circuit design,making them easy to replace?

[pieman103021]

better seal,would cause heating issues too.Why not create a circuit design,making them easy to replace?

That is not always an option. Depending on the application the circuit might not be able to be repaired or even be accessed.

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[james_s]

Are the red Roederstein and Siemens "Bakelite" capacitors considered sealed?

Audiophiles seem to like them. They claim the sound is as if a veil is lifted and the transistor sound undergoes vastation.

I've had to replace a bunch of those in Bosch ECUs and VDO gauges, they sure don't seem any more reliable than the normal rubber sealed type. I don't think loss of electrolyte is the only failure mode, I suspect it also chemically changes, perhaps it breaks down via electrolysis.

[Electro Detective]

Manufacturers won't cook their golden goose just yet   

You can count on leaking capacitors and spewing batteries to keep bunnies consumers spending solid for a few years more, and keep the landfills topped up.   

That said, I have seen better quality capacitors on some PC motherboards and graphics cards, which 'look' less likely to leak 

I only buy stuff for myself to keep long term ONLY if I know I can get to the caps and replace them EASILY, and keep a log book/reminder notes on batteries in multimeters   

[BravoV]

Read this -> http://www.chemi-con.co.jp/e/catalog/pdf/dl-e/dl-sepa-e/dl-precaution-e-170401.pdf

Especially the whole 5.1

[james_s]

Manufacturers won't cook their golden goose just yet   

You can count on leaking capacitors and spewing batteries to keep bunnies consumers spending solid for a few years more, and keep the landfills topped up.   

That said, I have seen better quality capacitors on some PC motherboards and graphics cards, which 'look' less likely to leak 

I only buy stuff for myself to keep long term ONLY if I know I can get to the caps and replace them EASILY, and keep a log book/reminder notes on batteries in multimeters   

There's no conspiracy to make capacitors fail early and keep people buying new equipment, that's just a side effect. It's all about cost, most companies if given a choice between a component that costs 9 cents each and lasts at least as long as the warranty and a component that costs 10 cents each and lasts 3 times as long they'll go with the cheaper part. Most consumers don't know any better, they shop entirely by price and will buy the cheaper item rather than a more expensive one that looks similar. The ultimate result is that virtually everything is engineered down to the lowest possible cost while being just good enough that the masses will still buy it.

[Electro Detective]

and that is why capacitors and batteries will keep leaking into the next century and beyond... don't fix it if it ain't broke = $$$$$$ 

[stj]

they make them too small to handle the current IMO.
look at the smd electrolytics - nothing but trouble.
they leak a lot and you cant even see it for ages.

what we need is shit polymers.
ones with higher esr so they can replace general to mid-tier electrolytics.

[wraper]

most companies if given a choice between a component that costs 9 cents each and lasts at least as long as the warranty and a component that costs 10 cents each and lasts 3 times as long they'll go with the cheaper part.

Price difference is much higher, many times, not 10%. And there is no explicit border between bad and good. Often cheaper parts last longer than many much more expensive counterparts and there is no guarantee that expensive parts won't fail prematurely. Like plagued Nichicon HM,HN and Chemi-con KZG, KZJ.

[T3sl4co1l]

The paradox of quality is this: a low quantity item is either going to be very unreliable (or its actual reliability very poorly established) -- because a large sample size does not exist -- or very expensive and carefully analyzed (like aerospace components are).

In massive commercial production, you get both high quantity and high quality.  It is generally in the manufacturer's best interest to pursue high quality, because it's cheaper to fix it on the front end -- refine the industrial process -- than to test quality into the part.

"Testing quality into a product" is something that can be done for products that are quick to test, and which fail due to random fabrication defects rather than subsequent stresses and aging.  Semiconductors are a great example.  Capacitors are a terrible example -- spending a few extra seconds on the tester tells you nothing about the 3 month+ survival rate of the component in actual use.  (Instead, a sampling approach with accelerated aging is needed, assuming the offending mechanisms can be accelerated proportionally.  Results still take a long time to obtain, at which point the product has long since been shipped and used.)

Tim

[David Hess]

I suspect the changes leading to lower design lifetimes were:

1. A greater use of switching regulators leading to capacitors selected for ESR rather than the capacitance needed for holdup time.  Notice that switching regulator input capacitors rarely fail.
2. A better understanding of the relationships between ESR, ripple current rating, and operating life.
3. Better specified capacitors.

The above allows the operating life of the device to be closely determined and limited.