Aluminium type capacitor with dielectric having extremely thin aluminium oxide is referred as electrolytic capacitor. These capacitors are cheap and have very large values upto 150000 µF. They are used in power supplies.
Electrolytic capacitors have polarities. Positive terminal is marked as + (positive) and can itself is the negative terminal. The DC leakage current maintains oxide layer otherwise reversed layer will cause layer to get deteriorated.
Tantalum electrolytic capacitors are used in place of aluminium in low voltage electronic circuits where required values are less than 100 µF.
Electrolytic capacitor polarity
Due to their characteristics, electrolytic capacitor must be forward biased i.e. voltage at positive terminal should be higher than the negative terminal. Please note that electrolytic capacitor polarity need to be considered while connecting it with the circuit. If not there is a chance of failure under reverse biased conditions as described below.
Electrolytic capacitor failure
When the capacitor becomes reverse biased the dielectric will be damaged and results into short circuit between the two capacitor terminals. This results into heavy current flow through capacitor. This will cause capacitor to overheat and leaks or vaporizes. Sometimes enclosure will burst. This is referred as electrolytic capacitor failure.
This process usually can occur at reverse voltage of about 1 volt and above. To avoid failure situation safety valve is inserted in the enclosure.
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