Why doesn't everything use solid aluminium capacitors?

[Commander Kinsey]

Motherboards used them over a decade ago, so why do I still find leaking electrolytics in TVs?

[Fredxx]

Cost.

[Paul]

They're polymer capacitors (polymer takes place of liquid electrolyte) and are used selectively in equipment. See the second picture down on the right, for a typical appearance. They lack pressure relief seams.

After the "capacitor plague", where poorly made (bad pH value) electrolyte was used to make some capacitors, some motherboard makers sought to "distance themselves" from electrolytics. The slightly different shape of the polymer capacitors was a "see, ma, no leaky cans" kinda thing. It was a visual distinction, intended to fool/convince buyers that they had nothing to fear. Before that introduction, polymer caps were already being used on video cards. They were more popular there. They're probably also a bit more expensive.

In the retail motherboard business, the customers see what's on the motherboard. You have to market to appearances.

In your TV set, the components are not exposed in the same way. Marketing consists of "look, thin bezels", or "now with built in spyware". No mention is made of what corners are cut in the power supply section. If you look at LCD monitors and the power board in there, the absolute cheapest manufacturing is used for the power board (sorta the equivalent of what you'd find in a $20 ATX PSU).

There is nothing wrong with electrolytic capacitors if they're made properly. Consequently, just because you find a cap with a pressure relief pattern embossed in the top of the cap, is no reason to panic.

It's hard to say whether any scumbag is still making caps using that stolen/incorrect electrolyte formula.

And as to "why do people continue to do bad things", it's a calculus. "Will I be executed or put in jail?" That's the question they have to ask themselves every day.

"22 May 2019 Ozone layer: Banned CFCs traced to China say scientists"

Paul

[Commander Kinsey]

citor-motherboard-line?

I've repaired many TVs from big manufacturers all with leaking capacitor= s. It's clear that they all wear out after a while, especially in hot e= nvironments.

And cost and size is not a problem, they're pretty much the same:

I tried to find the cheapest normal and solid capacitors on Ebay, as an = example 270uf, 16V: Normal:

Solid: =A33.94 for normal, =A33.83 for solid, so pretty much the same price. Sizing also almost equal: 12x9mm vs 12x8mm (the solid ones are slightly = smaller)

[Commander Kinsey]

citor-motherboard-line?

I tried to find the cheapest normal and solid capacitors on Ebay, as an = example 270uf, 16V: Normal:

Solid: =A33.94 for normal, =A33.83 for solid, so pretty much the same price. Sizing also almost equal: 12x9mm vs 12x8mm (the solid ones are slightly = smaller)

[Brian Gaff (Sofa 2)]

Stop excessive crosposting...

I suppose cos they can get them el chepo. I also have found toward the end of the 90s, those little tantalum caps that look like blobs of resin coloured blue tend to go leaky and damage the rest of the circuit. Nothing is supposed to last any more. Brian

[Commander Kinsey]

What's wrong with crossposting? There are 4 groups where people might know the answer. Yes, I could post 4 times seperately, but then people wouldn't see each other's replies.

I've checked both Ebay and Alibaba (where you can buy huge bulk quantities), and the prices are no different.

I've never seen the tantalum ones break.

[alan_m]

I remember working on (expensive) test equipment in the 80s and a common failure mechanism with the tantalum bead capacitors was a short circuit taking out other components.

[Commander Kinsey]

Were those visibly obviously damaged? It's just I've never seen one fail, and was wondering if I could tell from a visual inspection. The electrolytics have clearly failed when they bulge or burst - I see it all the time in old/cheap motherboards, or inside TVs.

[Paul]

This is copied from the web page of a capacitor company.

Pros of aluminum electrolytic capacitors:

Higher voltage ratings available (up to 600V) Way cheaper pricing (for the same capacitance and voltage) Better leakage current behavior than polymer

Pros of polymer electrolytic capacitors:

Lower ESR/higher allowable ripple current No dry-out behavior (unlike aluminum capacitors) Higher expected lifetime/load life

And while one biased company claims electrolytics dry out after 3 years (a made up number), another company (likely using field statistics for their own capacitors) finds the time constant is 17 years. And I would have to conclude that the 17 year number is likely to be closer to the truth (based on old computers still in a running state, like my first computer from

1998-1999 or so which still operates just fine).

The Arrhenius effect is for real, and operating even the best electrolytics at high temperature, doesn't end well. At the highest allowed temperatures, some of these electrolytics (by calculation) should only last for 2000 hours. That's what the curve fit data for accelerated life testing shows. When I say a number like 17 years, it would be in an item with proper and copious cooling. Note that electrolytics themselves get warm in service, depending on the ripple current being forced through them. The plastic sleeve on the outside, does not enhance cooling for those situations. The capacitors in VCore (on the primary or secondary side) could be experiencing high ripple currents. And if any are to fail, those should go first. The "bulk" decouplers placed near a PCI or PCIe slot, those aren't under nearly the same stress level.

HTH, Paul

[Commander Kinsey]

There are three types of capacitor we should be considering here:

Standard electrolytic. Aluminium electrolytic. Solid aluminium.

The last two are not the same.

[Bob Eager]

That's the big problem with tantalums - they almost always fail short circuit.

[alan_m]

Temperature, both rated and operating, is a factor. As I understand it a rating of,say, 7000 hours at 105C means for every 10C lower actual operating temperature it doubles the lifetime. Operating them at 65C will give approx 12 years of continuous use.

In a old computer the power supply always had it's own fan keeping the unit relatively cool. In modern TVs, set top boxes etc the room for a noisy fan giving a decent air flow is somewhat limited and temperatures within many boxes are 60C+. Many capacitors in switched mode supplies also seem to be fitted very close to hot heat-sinks! In my experience it's usually the power supply capacitors that have an early failure.

Some manufactures will fit capacitors rated at 7,000 hours at 85C so when operating at 65C the life expectancy is closer to 28,000 hours (3 years continuous use).

There is also a problem with life expectancy from self heating due to the Equivalent Series Resistance (ESR). For a switched mode supply a capacitor with a low ESR is required. A decade or so ago I read a technical report from one of the more respected capacitor manufacturers (Rubicon I think) where they claimed that they used physically larger cans/packaging than some of their Korean competitors to ensure lower ESR figures. I always found that when changing duff electrolytic with Korean brand names such as SamYoung etc. that the replacements from a variety of reputable brands were physically larger - usually the same diameter can but the height of the can was maybe 5mm more.

I've had capacitors fail in a couple of PVRs after a couple of years but carefully selected replacements lasted close to 10 years.

[Ralph Mowery]

It is not only the cheep or China parts that fail. I have a couple of pieces of HP test gear that I bought surplus that the capacitors have failed in the power supplies. They origionally sold for about $ 50,000 each back in the mid 1990's. I guess that about 20 years is not too bad for them. Not sure how many hours they may have had on them.

[Commander Kinsey]

Well there seem to be loads of them about. A 15 amp 13.8V PSU I bought brand new had one fail after only 3 months use. And it was only used to about 5A. It's been happy ever since I put a better one in.