What Is The Capacitor Plague The capacitor plague is a problem with a large number of premature failures of aluminium electrolytic capacitors with non solid or liquid electrolyte of certain brands especially from Taiwan manufacturers. The first flawed capacitors were seen in 1999, but most of the affected capacitors failed in the early to mid 2000s. They failed in various electronics equipment News of the failures (usually after a few years of use) forced most manufacturers to repair the defects. The problem seems to be ongoing still being reported as of 2012. A capacitor a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric material common construction consists of metal foils separated by a thin layer of insulating film. When there is a potential difference across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called plates, referring to an early means of construction. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance. The first electrolytic capacitor ever was an aluminium electrolytic capacitor with a liquid electrolyte, invented by Charles Pollak in January 1896. In principle, the electrolytic capacitors up to this day remained the same. A aluminium anode, the dielectric out of very thin aluminium oxide. The liquid electrolyte adapts the structure of the dielectric, forms the liquid cathode of the capacitor and thus makes the thin layer thickness of the dielectric effective. A spacer made of paper prevents direct contact of the oxide layer with a second aluminium foil (cathode foil), which provides the electrical connection to the liquid cathode. Sealed and provided with connections, this construction results in billions of inexpensive and within their life span reliable capacitors used for electronic devices. The electrolyte as ionic conductor caused most of the ohmic losses in the capacitor. Great efforts have been made over the years to reduce these losses to increase the ripple current, because without such improvements the most important target of development — size reductions — cannot be realized. In Japan, in the context of these developments, some manufacturers are busy to develop a new, low-ohmic water-based electrolyte. The conductivity of water-based electrolytes compared to electrolytes with organic solvents like GBL was significantly improved. Water, with its relatively high permittivity of ε = 81, is a powerful solvent for electrolytes. As such, it dissolves salts in high concentration. The high concentration of dissolved salt ions in the electrolyte increases the conductivity. But water will react quite aggressive and violently with unprotected aluminium. It converts aluminium (Al) with a highly exothermic reaction into aluminium hydroxide (Al(OH)3). This is accompanied by a strong heat and gas development in the capacitor and may lead to the explosion of the capacitor. Therefore, the main problem in the development of new water-containing electrolytes, is to hinder the aggressiveness of the water against aluminium to get capacitors having a sufficiently good long-term stability. A probable cause of the plague was industrial espionage in connection with the theft of an electrolyte formula. An electrolyte developer is suspected of having taken, when moving from Japan to Taiwan, the chemical composition of a new low resistance, inexpensive, water-containing electrolyte. The developer subsequently tried to counterfeit this electrolyte in Taiwan, then to sell it cheaper than the Japanese could, but the formula had apparently been copied incompletely, and it lacked important substances essential in securing the long-term stability of the capacitors.
Posted on: Fri, 28 Mar 2014 21:38:34 +0000
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