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Aluminum Electrolytic Capacitors

Date: 2015-12-11
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Electrolytic capacitors are also very common and are found in the quintessential “can” body. These capacitors are constructed from a piece of paper soaked in electrolyte sandwiched between two pieces of aluminum foil. One piece of foil, the anode, has a coating of aluminum oxide. This coating acts as the dielectric between the two electrodes. The electrolytic paper is electrically conductive, but has chemical properties that allows it to heal the oxide layer should it become damaged. The combination of aluminum oxide dielectric and electrolytes allow for very high capacitance values in a small package. The three layers are rolled together and sealed in a cylindrical aluminum housing.


The aluminum oxide layer allows for the flow of current in one direction, which is a problem for capacitors. As a result, electrolytic capacitors cannot be used to couple AC signals. If the capacitor sees a reverse voltage or over-voltage, the aluminum oxide layer breaks down and a short circuit occurs between the electrodes. As current flows through the paper spacer, the electrolyte heats up, often resulting in the capacitor leaking or bursting. Most modern electrolytic capacitors have a seal at the end of the can which cracks open to relieve the built up pressure in the event of a failure. Once this happens, the capacitor is no longer useful, but it will generally fail open.


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