An ultracapacitor, also called a supercapacitor, is an electrical component capable of holding hundreds of times more electrical charge quantity than a standard capacitor. This characteristic makes ultracapacitors useful in devices that require relatively little current and low voltage. In some situations, an ultracapacitor can take the place of a rechargeable low-voltage electrochemical battery.
The principal disadvantage of the ultracapacitor, compared with older capacitor designs, is the fact that the ultracapacitor cannot withstand high voltage. While an electrolytic capacitor might be rated at several hundred DC volts, ultracapacitors have maximum ratings of only about 5 DC volts. In order to use ultracapacitors at higher voltages, multiple components must be connected in series (end-to-end, like the links in a chain). Then their voltage ratings add up, just as battery voltages add in a series connection.
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Reference: TechTarget - WhatIs.com