Structure and special features of aluminum electrolytic capacitors
In aluminum electrolytic capacitors, the anode and cathode consist of highly roughened aluminum foils, whereby the roughened anode foil with the dielectric layer is rolled up between an absorbent material (usually paper). This paper later absorbs the liquid, electrically conductive electrolyte and thus ensures that the entire surface of the surface of the anode foil is contacted. On the other side, the electrolyte is in contact with the cathode foil and connecting tabs on both foils lead to connecting wires for connection to the circuit.

It should be emphasized that electrolytic capacitors are polar. They must therefore be installed with the correct polarity and may only be operated with DC voltage. The anode is always the positive pole. Excessive voltages or incorrect polarity destroy the dielectric layer, which can lead to short circuits or even explosions. For this reason, the correct polarity must always be ensured and a polarity marking must be applied to all electrolytic capacitors. By the way: In many radial capacitors, the positive pole of the anode is longer than the wire of the cathode.

The most special feature of the electrolytic capacitor is the liquid cathode, the electrolyte. Since electrolyte continuously leaves the electrolytic capacitor can by diffusion, aluminum electrolytic capacitors dry out due to their design and change their electrical parameters. Drying out and thus the rate of aging are strongly temperature-dependent: they double with every 10 K increase in temperature! This leads to a finite lifetime of aluminum electrolytic capacitors, which is characterized by a parametric failure. In the event of a parametric failure, the electrolytic capacitor keeps its function, but falls below or exceeds predefined limits for capacitance, ESR and leakage current.

The aluminum oxide layer grows on the anode foil by means of an electrochemical process (“anodic oxidation” or “forming”). The oxide is very thin and at the same time very voltage-resistant, which means that electrolytic capacitors have a comparatively high specific capacitance compared to other types of capacitors, which is only exceeded by so-called supercapacitors (listed as “Energy-C” at Jianghai).

The dielectric strength of electrolytic capacitors, which is determined by the properties of the oxide layer in the dielectric, refers to the voltage (= rated voltage) that an electrolytic capacitor can withstand in the long term without a breakdown occurring. As the ambient temperature increases, the voltage withstanding capability of the oxide layer decreases. It is therefore advisable to operate aluminum electrolytic capacitors permanently below the specified rated voltage and the upper category temperature, as this has a positive effect on the lifetime and the expected failure rate of the product. In addition, the self-heating of electrolytic capacitors under current load must always be kept in mind. Thermal radiation and convection are the main cooling mechanisms of electrolytic capacitors. Forced cooling can significantly increase the proportion of convection and thus extend the lifetime.


Additional information on aluminum electrolytic capacitors and polymer (and others) can be found in our

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What parameters can you find in the datasheet of Jianghai capacitors? 


Datasheets for Jianghai capacitors contain a lot of information that makes it easier to find the right electrolytic capacitor. These parameters, among others, are of particular importance:

What designs of aluminum electrolytic capacitors does Jianghai offer?

Aluminum electrolytic capacitors often act as buffers for sudden load peaks. They are therefore used, for example, as energy storage devices in power supplies or DC intermediate circuits in  frequency converters.