Capacitors Are Simple, Right?

It is easy to dismiss passive components like resistors and capacitors as a boring subject. [James Lewis] of KEMET Capacitors would disagree. He gave a talk about capacitor tech that is both approachable and in-depth.

Like every other component we use, we always think of them as perfect. But just like wires have resistance and inductance that we often ignore, capacitors have different imperfect characteristics that you need to be aware of.

Ceramic capacitors, for example, lose capacitance over time. Different ceramic material have different temperature sensitivity. Aluminum capacitors don’t last forever. Voltage applied to a capacitor can change its value as much as 50%.

[James] also talks about polymer electrolytics and super capacitors. His burning question: Is there any truth to the old guideline that you should derate capacitors by 50%? Want to know what he thinks? Watch the video below. Speaking of burning, he tackles the touchy subject of tantalum capacitors. The image at the top is a test Kemet ran on their own parts at reverse polarity well beyond spec. All of them are blown but only some look burnt. That’s a mystery well worth watching the talk.

The presentation, by the way, was from the Hardware Developer’s Didactic Galactic — a recurring set of hardware talks held at Supplyframe’s San Francisco office (and, for the record, Supplyframe happens to own Hackaday). If you want to read more about capacitors, you might enjoy our recent coverage of capacitor types. If supercapacitors strike your fancy, you can always grab some lint and dog hair.

25 thoughts on “Capacitors Are Simple, Right?

  1. One of the tantalum bulk decoupling on the power supply for a prototype was installed backwards. The card would run for a minute or so and then crashes. The cap triggered the over current protection of the switch mode supply which was easily 6-7A. It took a couple of days for the guy to even notice that the cap was heating up to find the problem.

    The cap used was AVX TPS series.

  2. Poor quality Chinese capacitors are the bane of consumers products that FAIL long before they should. They are also the best thing that ever happened to OEM’s => “Planned Obsolescence”.

    And don’t even get me started on flat panel displays and FAIL’ed zebra cables.

    1. Well I had things with japanese capacitors where it failed, and I have decades old devices with no name capacitors that are fine. I don’t think it’s all as simple as ‘blame the chinese’. Unless that’s the thing you are going for.

        1. Actually, you can blame the Chinese

          “Industrial espionage was implicated in the capacitor plague, in connection with the theft of an electrolyte formula. A materials scientist working for Rubycon in Japan left the company, taking the secret water-based electrolyte formula for Rubycon’s ZA and ZL series capacitors, and began working for a Chinese company. The scientist then developed a copy of this electrolyte. Then, some staff members who defected from the Chinese company copied an incomplete version of the formula and began to market it to many of the aluminium electrolytic manufacturers in Taiwan, undercutting the prices of the Japanese manufacturers”

          1. The “Capacitor Plague” was a thing but it ended – well sort of. (only electro’s considered)

            Now days there two main causes of capacitor caused failures and one has been there all along.

            1) Capacitors dry with age and when they do their equivalent series resistance increases and this in effect (where there used for power filters) reduces their capacity. The two things to remember in design are 1) You need to de-rate for longevity. In any case their going to be dead in 8 to 15 years and 2) Capacitors have an effective resistance and also increased temps are harmful to them. The thermal power can be calculated and their surface area should be taken into consideration. A small cap will die faster than a larger one. Most people think it is the voltage rating but it’s just the fact that higher voltage caps have a larger surface area.

            2) The China thing didn’t go away. I have seen large can capacitors that are empty cans except for a much much smaller capacitor inside.

      1. The Japanese were the first to develop cheap water-based low ESR electrolytes for aluminium capacitors, so it stands to reason that they were also the first ones to make dodgy ones and push them on the market.

        The water based electrolytes – when imperfectly made – evolve hydrogen´and eventually fail, which the organic solvent based capacitors do not. The noname companies would likely use older organic solvents and in non-critical applications with no excessive ripple currents, that would be just fine.

        1. F*** Comment system. There is a “reply” button, when there is just one button, you click that… Turns out SOMETIMES the reply button is hidden. That’s when people get REPORTED because that’s the only button rendered. Sigh. Sorry RÖB.

          ….. higher voltage caps have a larger surface area…..
          …. large can capacitors that are empty cans except for a much much smaller capacitor inside. …

          A least they have a larger surface area…. ;-)

  3. Awesome and engaging presentation. I learned a couple of things I didn’t know before that will change my design procedure for selecting capacitors. Another source of information on capacitors (basic principles) that I recommend is a small book called “ABC of Capacitors” by Wurth Electronics.

    1. The point is that they’re tested at a certain voltage, and then soldering causes cracks in the dielectric that cause failures on power-on, and de-rating the part decreases the probability of failure.

      The part can be healed to the full rated voltage by slowly ramping up the voltage/current but it is generally not done and instead manufacturers choose to just use twice rated parts.

    2. He was talking about [i]ceramics[/i] needing to be derated.
      I use 6.3V tant csps in a 4.2V application, never failed. One did blow up when I installed it backwards. Who cares that they blow up like a ton of other electronic parts? It just sends the top .5mm flying off.
      Its amazing you can get 6V/100uF in a ~3x2x1.5mm form factor.

    3. Using them at half the voltage will reduce the number of explosions from a few per thousand to a few per million produced products.

      I like the exploding tantalums. You know something is wrong when it explodes. The neat, not-discolored failed caps are way more difficult to diagnose.

  4. That was 50 minute well spent, if only this article was posted a while back, it sure would have helped to shut up a few trolls spouting decades out of date opinions. LOL at the line ” tin is also a conflict material and I don’t hear anyone complaining about that.” storms in tea cups, all the first world supplies are as clean as is practical anyway.

    The fact that the tantalum manganese caps can be pretested is interesting, even if those old ones are now being replaced by less energetic poly designs.

  5. I have lost count the number of LED mains “bulbs” I have had fail.
    Pop them open, and the 240V rated cap has gone splat.(Am in the UK)
    Swap it for a same value 400V rated one and they are good to go.

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