Thursday, May 19, 2011

Why certain capacitors explode?

Electrolytic capacitors which are polarized will explode if a reverse voltage of > 1.5 volts is applied. But why? Read on to find the answer.

C = (E0 * Er * A)/d, where A is the area and d is the distance between the plates.
The construction of an electrolytic capacitor is as shown in the figure below:
Internals: Electrolytic capacitor
Electrolytic capacitors are constructed using an electrolyte-soaked piece of tissue paper between two strips of metal aluminum foil. One piece of foil is oxidized, and this ultra-thin oxide coating acts as the dielectric. The rolling of the capacitor helps to achieve a high area (in the formula above), and hence a good capacitance. Since this capacitor is polarized, passing a revers current removes the oxide coating resulting in almost a short circuit. This leads to a further increase in temperature and pressure in the hermetically sealed container eventually leading to an explosion.

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