Structure, Function, and Problems of Electrolytic Capacitors

Construction, Function, and Problems of Electrolytic Capacitors

Electrolytic capacitors generally consist of two long, thin aluminum strips, each welded to one of the capacitor's leads and rolled up into a small coil.

To function as a capacitor, the two aluminum strips must not have any electrical contact with each other. Therefore, a somewhat wider strip of paper is placed between them. In special capacitors, more refined materials, such as silk (in the form of fabric made from it or a type of "silk paper"), may also be used.

These absorbent strips are soaked in a liquid, the electrolyte. Together with the paper strips, the electrolyte forms what is known as the dielectric, separating the two types of charge, positive and negative, from each other.

The electrical value of an electrolytic capacitor is determined by the length and width of the strips, the distance between them (the paper strip), and the amount of electrolyte contained in the paper strip.

Although electrolytic capacitors with liquid electrolyte, which are the main focus of this shop, are hermetically sealed with a rubber plug, the electrolyte can still evaporate over time, for example through aging of the rubber plug around the lead feedthroughs, through nearby components that become hot, or through increased internal pressure caused by heating under load.
When old equipment is reactivated, storage conditions in a hot environment (storage room, attic) may also have played a role.

However, as the paper strips become drier, the capacitor loses more and more of its capacitance.
It can therefore perform its originally intended function at its installation location less and less effectively, eventually not at all.
It is then as if there were no component at that point capable of having any significant influence on what is happening (see below: Effects on hi-fi equipment).

Electrolytic capacitors that have burst are also frequently seen.
This may be related to an incorrectly formulated electrolyte liquid and/or heavy load accompanied by self-heating.
Corrosive electrolyte may then leak out and damage circuit traces and other components. In most cases, however, the substance found around large electrolytic capacitors is adhesive, which was intended to additionally secure the capacitors during transport.

Incorrect sizing with regard to voltage rating, or the higher mains voltage today, may also cause this.

Voltage Rating

Since 1987, the mains voltage has been increased from 220V (198V-242V possible) to approximately 230V (207V-253V possible) as part of Europe-wide harmonization.

Because electrolytic capacitors usually smooth the voltage immediately after the transformer and rectifier, with voltage regulation taking place only afterward, many such capacitors are now operated above their permissible voltage. Their voltage ratings were often calculated very narrowly because of their size (particularly noticeable in Philips CD players).

It is therefore strongly recommended that equipment that can be switched from 220 to 240V be switched or rewired accordingly (unfortunately, some devices do not offer this option).

Capacitors have become smaller over time, so physical size is no longer a disqualifying criterion for a higher voltage rating.

Effects on Hi-Fi Equipment

In the case of an analog amplifier, this may be noticed through hum in the speakers (increasingly inadequate filtering of the rectified mains voltage), imbalances between the two channels, distortion in playback, or failure of the protection circuit, which is supposed to switch on the speakers only after some time when the device is turned on (the speakers remain off for an extremely long time or switch on immediately without the protective effect).

Because CD players mainly use digital signal processing, faulty capacitors expose their circuitry to unfiltered interference, which can increasingly make it difficult to read the CD, cause the player to "act crazy" after some time, or require a certain "warm-up period" after switching on before it can be used for "normal" listening.

Such players may also no longer be able to process perfectly read CD information without interference. The effect is comparable to a heavily scratched CD, where the player has to reconstruct (interpolate) the missing information, which can never be done without loss.

Before suspecting an unobtainable defective laser as the source of the problem, it may be worthwhile to install, or have installed, a new set of capacitors (unfortunately, we do not offer this service).


Is Readjustment of the Device Absolutely Necessary After Installation?

In general, our position is that a device with adjustable parameters, which was perfectly calibrated at the factory when the capacitors were still new and unused, will be brought substantially closer to its original condition by installing a new set of capacitors than by replacing only "the usual suspects."

Over time, the calibration shifted as the electrolytic capacitors aged, until the device may eventually have ceased to function.

Installing a completely new set of capacitors restores the condition as it was at the factory, although it should of course be noted that both the old capacitors when they were new and the new ones were or are subject to manufacturing tolerances.

With tuners, readjustment is therefore definitely recommended if these electrolytic capacitors are located in the RF-processing section of the circuit. This is rarely the case, however, as other types of capacitors are more commonly found there.