If an aluminum electrolytic capacitor has a reverse voltage applied, its capacitance will decrease, its leakage current will increase and the capacitor may explode. Besides the application of a reverse voltage, overvoltage, AC voltage or capacitor failure, internal gas pressure can be generated at a rate the package cannot contain mechanically.
Aluminum electrolytic capacitors are (usually) polarized electrolytic capacitors whose anode electrode (+) is made of a pure aluminum foil with an etched surface. The aluminum forms a very thin insulating layer of aluminum oxide by anodization that acts as the dielectric of the capacitor.
This guide covers the application of polar, non-solid aluminum electrolytic capacitors, which are those aluminum electrolytic capacitors featuring a wet, aqueous electrolyte with separator membranes such as cellulosic papers between two aluminum foils.
Aluminum electrolytic capacitors have a polarity. When reverse voltage is applied, current flows and formation of oxide film progresses until withstand voltage of the cathode matches the applied voltage, resulting in decrease in capacitance, increase in tan δ (ESR), and gas generation.
The anode of an aluminum electrolytic capacitor is an aluminum foil of extreme purity. The effec-tive surface area of this foil is greatly enlarged (by a factor of up to 200) by electrochemical etch-ing in order to achieve the maximum possible capacitance values.
Aluminum electrolytic capacitors with non-solid electrolytes normally can be charged up to the rated voltage without any current limitation. This property is a result of the limited ion movability in the liquid electrolyte, which slows down the voltage ramp across the dielectric, and the capacitor's ESR.