Not all electrolytic capacitors are manufactured equally. Japanese and solid caps have better quality, protecting your equipment from the infamous capacitor leakage problem and also increasing the life-span of your equipment, especially if it works at high temperatures, like it is the case with power supplies. In this short tutorial we will teach you how to identify Japanese capacitors and why they have a better quality.

Solid and electrolytic capacitorsFigure 1: Solid and regular electrolytic capacitors

In order for you to understand why solid and Japanese capacitors are better, let’s explain what a capacitor is and how electrolytic caps are manufactured. By the way, solid aluminum capacitors are also electrolytic capacitors but using a different packaging.

The main goal of a capacitor is to store electric charges. The amount of electric charge it can store is given in a unit called coulomb. The capacitance of a capacitor is how much electric charge it will store for each volt applied on its leads, given in a unit called farad (F). Capacitors used in consumer electronics products are measured far below 1 farad, usually on the picofarad (pF, which equals 0.000,000,000,001 F) range for ceramic capacitors, on the nanofarad (nF, which equals 0.000,000,001 F) for polyester capacitors and on the microfarad (µF, which equals 0.000,001 F) for electrolytic capacitors.

Capacitors are manufactured putting two metallic foils parallel to each other, with a material – called dielectric – between them. Depending on the dielectric material the capacitor can store more or less electric charges, and the material used gives the name of the type of capacitor. As you can see on the previous paragraph, electrolytic capacitors can store more electric charges than polyester capacitors, which in turn can store more electric charges than ceramic capacitors. Keep in mind that a capacitor that can store more electric charges isn’t better than a capacitor that can store less electric charges. Each capacitance has a different application.

Electrolytic capacitors are made with two aluminum foils placed parallel to each other, with an absorbent material wet in an electrolyte (i.e., liquid material) placed between them – hence the name of this kind of capacitor. Then this “sandwich” is spiraled.

The whole problem of electrolytic capacitors is that the electrolyte tends to dry out, degrading the capacitor (i.e., making it to lose its storage capacity), causing a mal-function on the circuit where it is installed. For example, one of the most popular uses for electrolytic capacitors is on filtering circuits and if the capacitor has gone bad the filtering simply won’t happen, which will cause a malfunction on the circuit after the filtering stage. A PC power supply with bad a filtering stage would deliver voltages with a huge fluctuation, causing malfunction or even burning your motherboard, hard disk drive, etc.

As you can imagine, the liquid inside the capacitor will only dry out if the capacitor isn’t perfectly sealed and/or if the capacitor is exposed to high temperatures (the definition of “high temperature” for us is any temperature above the standard room temperature of 25° C or 77° F).

But this is not the only problem that can occur. If the capacitor isn’t perfectly sealed the liquid inside the cap can leak, and it can even corrode the printed circuit board where the capacitor is installed.

Also the electrolyte inside the capacitor can vaporize under high temperature (or if a voltage higher than the maximum allowed is applied), creating a pressure on the capacitor case, making the capacitor to swell or even explode.

All capacitors have temperature and voltage markings. Temperature is usually rated at 85° C (185° F) or 105° C (221° F). These numbers should be far above the actual figures that will be used, the higher the better. If these numbers are exceeded, the above problems can occur. But of course under normal usage of a circuit this won’t occur, unless someone placed a capacitor with wrong specs by mistake in the circuit.

The two main problems with electrolytic capacitors are the use of a bad sealing and the use of a bad electrolyte. A bad sealing will make the electrolyte to leak or evaporate. And a bad electrolyte can do lots of stuff, the most common ones being vaporizing at a temperature lower than the temperature printed on the capacitor label (making the cap to swell or to explode) and corroding a cheap sealing material and leaking.

Japanese capacitors are notoriously known by their above-the-average quality (good electrolyte and good sealing), while Chinese capacitors have the bad reputation of using cheap electrolyte and cheap sealing, what can lead to the problems we explained. Solid capacitors are also immune to the above problems as they provide the best possible sealing.

Identifying solid capacitors is easy, as they have a complete different physical aspect (see Figure 1). But how can you tell whether a given electrolytic capacitor is Japanese or not?


Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.