Faulty Electrolytic Caps Don’t Always Look Bad

July 18, 2021 by Donald Papp 49 Comments

Old electrolytic capacitors are notorious for not working like they used to, but what exactly does a bad capacitor look like, and what kinds of problems can it cause? Usually bad caps leak or bulge, but not always. In [Zak Kemble]’s case, a bad cap caused his Samsung HT-C460 Home Cinema System to simply display “PROT” then turn itself off. Luckily, replacing the troublesome cap fixed everything, but finding the problem in the first place wasn’t quite so straightforward. A visual inspection of the device, shown open in the photo above, didn’t reveal any obvious problems. None of the capacitors looked anything out of the ordinary, but one of them turned out to be the problem anyway.

The output cap had developed an internal short, but visually looked fine.

The first identifiable issue was discovering that the -5 V supply was only outputting about -0.5 V, and there was a 6 V drop across two small 0805-sized resistors, evidence that something was sinking far more current than it should.

Testing revealed that the -5 V regulator wasn’t malfunctioning, and by process of elimination [Zak] finally removed the 470 uF output capacitor on the -5 V output, and the problem disappeared! Inspecting the capacitor revealed no outward sign of malfunction, but it had developed an internal short. [Zak] replaced the faulty cap (and replaced the others just to be safe) and is now looking forward to getting years more of use out of his home cinema system.

When a PSU gives up the ghost, bad capacitors are almost always to blame, but we’ve seen before that it’s not always easy to figure out which ones are bad. One thing that helped [Zak] plenty in his troubleshooting is finding a full schematic of the power supply, just by doing a search for the part number he found on it. A good reminder that it’s always worth throwing a part number into a search engine; you might get lucky!

New Part Day: SMD Batteries

January 16, 2019 by Brian Benchoff 60 Comments

Here’s a tip for all you retrocomputing enthusiasts or even anyone with an old computer in the garage. Go remove the battery. Yes, that old mid-90s desktop has a battery inside for the real-time clock, and it’s a ticking time bomb. Batteries leak, and they’ll spew goo all over the circuit board, irreparably damaging your piece of electronic nostalgia. This goes for all electronics, too: that badge collection is going to be a pile of broken fiberglass in a decade. Remove your batteries now.

While lithium cells soldered to a motherboard will leak, now there might be a new technology that will allow our modern electronics to last for decades. It’s a solid state battery. The FDK Corporation is now handing out samples of a battery that looks like a large SMD cap. They come on tape and reel, and they’ll never leak.

Thanks to massive investments in battery research, batteries are getting more power-dense, and form factors are getting weird. Your AirPods need a battery somewhere, and manufacturers are figuring out the best way to put a battery into something that can be assembled by a pick and place machine. This battery is the answer to these problems, packing a 3.0 V, 140 μAh lithium cobalt pyrophosphate cell into a package that is just 4 mm by 2 mm by 2 mm. It’s a battery that looks a surface mount component, and it’s installed the same way: this is a pick-and-placeable battery.

While the capacity of this battery is tiny — a 1225 coin cell has a capacity of about 50 mAh, and this battery has a capacity of 140 μAh, three whole orders of magnitude smaller — sometimes that’s all you need. If you need a battery for a RTC, this SMD battery will work.

The Components Are INSIDE The Circuit Board

September 11, 2017 by Bob Baddeley 56 Comments

Through-hole assembly means bending leads on components and putting the leads through holes in the circuit board, then soldering them in place, and trimming the wires. That took up too much space and assembly time and labor, so the next step was surface mount, in which components are placed on top of the circuit board and then solder paste melts and solders the parts together. This made assembly much faster and cheaper and smaller.

Now we have embedded components, where in order to save even more, the components are embedded inside the circuit board itself. While this is not yet a technology that is available (or probably even desirable) for the Hackaday community, reading about it made my “holy cow!” hairs tingle, so here’s more on a new technology that has recently reached an availability level that more and more companies are finding acceptable, and a bit on some usable design techniques for saving space and components.

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Capacitors Are Simple, Right?

July 9, 2016 by Al Williams 25 Comments

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.

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Box ‘o Bangs, A 2,180J Capacitor Bank

April 19, 2016 by James Hobson 35 Comments

What happens when you wire up 16 capacitors? Sixteen 2500V 40uF capacitors to be precise… [Lemming] calls it the Box ‘O Bangs. Theoretically it outputs 4000A at 2500V for a split second.

They bought the capacitors off of eBay, and they appear to be good quality BOSCH ones, straight from Germany. They were apparently used for large-scale industrial photo-flashes, but who knows since they’re from eBay.

Soldering it all together proved to be a challenge, as once they realized just how many amps this thing was going to put out, they needed some thick wire. It looks like about 2ga wire, which, spoiler alert, still isn’t enough for 4000A — but since it’s only for a split second it seems to do fine.

Once everything was built, it was time for some scientific tests — what can we put between the leads to explode? Stay tuned for some slow-motion glory.

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Better Capacitors Through Nanotechnology

October 25, 2015 by Al Williams 29 Comments

Traditionally, capacitors are like really bad rechargeable batteries. Supercapacitors changed that, making it practical to use a fast-charging capacitor in place of rechargeable batteries. However, supercapacitors work in a different way than conventional (dielectric) capacitors. They use either an electrostatic scheme to achieve very close separation of charge (as little as 0.3 nanometers) or electrochemical pseudocapacitance (or sometime a combination of those methods).

In a conventional capacitor the two electrodes are as close together as practical and as large as practical because the capacitance goes up with surface area and down with distance between the plates. Unfortunately, for high-performance energy storage, capacitors (of the conventional kind) have a problem: you can get high capacitance or high breakdown voltage, but not both. That’s intuitive since getting the plates closer makes for higher capacitance but also makes the dielectric more likely to break down as the electric field inside the capacitor becomes higher with both voltage and closer plate spacing (the electric field, E, is equal to the voltage divided by the plate spacing).

[Guowen Meng] and others from several Chinese and US universities recently published a paper in the journal Science Advances that offers a way around this problem. By using a 3D carbon nanotube electrode, they can improve a dielectric capacitor to perform nearly as well as a supercapacitor (they are claiming 2Wh/kg energy density in their device).

The capacitor forms in a nanoporous membrane of anodic aluminum oxide. The pores do not go all the way through, but stop short, forming a barrier layer at the bottom of each pore. Some of the pores go through the material in one direction, and the rest go through in the other direction. The researchers deposited nanotubes in the pores and these tubes form the plates of the capacitor (see picture, right). The result is a capacitor with a high-capacity (due to the large surface area) but with an enhanced breakdown voltage thanks to the uniform pore walls.

To improve performance, the pores in the aluminum oxide are formed so that one large pore pointing in one direction is surrounded by six smaller pores going in the other direction (see picture to left). In this configuration, the capacitance in a 1 micron thick membrane could be as high as 9.8 microfarads per square centimeter.

For comparison, most high-value conventional capacitors are electrolytic and use two different plates: a plate of metallic foil and a semi-liquid electrolyte. You can even make one of these at home, if you are so inclined (see video below).

We’ve talked about supercapacitors before (even homebrew ones), and this technology could make high capacitance devices even better. We’ve also talked about graphene supercaps you can build yourself with a DVD burner.

It is amazing to think how a new technology like carbon nanotubes can make something as old and simple as a capacitor better. You have to wonder what other improvements will come as we understand these new materials even better.

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Hackaday Links: November 2, 2014

November 2, 2014 by Brian Benchoff 16 Comments

Russians blowing up capacitors! As we all know, electronics only work because of blue smoke. [kreosan] is releasing this blue smoke from a few hundred caps. Fun times, even if they are a large number of inert tube shields in their collection of caps.

[mayhugh1] over on the home model engine machinist forum has built an 18 cylinder radial engine. It’s based on the Hodgson 9-cylinder radial engine that has been around for a while. The crank case is machined from a 5″ diameter rod of aluminum. There’s a Picassa album of the engine being constructed as well.

[Richard] wanted a Minecraft server, but not just any Minecraft server; this one demanded a custom case. A grass block was the inspiration, acrylic the medium, and a quad-core Mini-ITX the guts of the project.

Halloween was last Friday, and as always the tip line filled up with costume builds. [Leif] built a Ghostbusters costume complete with Muon trap, [Jeff] printed out some ~~steampunk~~ post-apocolyptic goggles, and [Green Gentleman] made a death-a-corn, although we’re struggling to figure out why the last one isn’t called an acorn-‘o-lantern.

[Matthias Wandel], a.k.a. the woodgears.ca dude, is well-known in certain circles for being a wizard of wood. One of the first projects that put him on the map was a pantorouter – a router to cut mortises and tenons. He’s going back to his roots and building a bigger version. This version uses models of routers that are available outside North America, and in the latest video [Matthias] has it dialed in very well.

The Open Source Remote Control was an entry for The Hackaday Prize that didn’t make the final cut. It’s now an indiegogo project, and has some really cool tech we can’t wait to see in mainstream RC transmitters.