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How An Ultra Capacitor Works

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Recent work at MIT's Laboratory for Electromagnetic and Electronic Systems (LEES) offers the most economically viable alternative to conventional batteries in more than 200 years. The Ultracapacitor is both a battery and a capacitor.


Ultracapacitors could allow laptops and cell phones to be charged in a minute. Unlike laptop batteries, which start to lose their ability to hold a charge after a year or two (several hundred charge/discharge cycles), ultracapacitors have hundreds of thousands of charge/discharge cycles and could still be going strong long after the device is obsolete. 'Theoretically, there's no process that would cause the [ultracapacitor] to need to be replaced.' says professor John Kassakian


Ultra capacitors & Super Capacitors store electricity by physically separating positive and negative charges— different from batteries which do so chemically. The charge they hold is like the static electricity that can build up on a balloon, but is much greater thanks to the extremely high surface area of their interior materials.
An advantage of the ultracapacitor is their super fast rate of charge and discharge... which is determined solely by their physical properties. A battery relies on a slower chemical reaction for energy. A disadvantage of an ultracapacitor is that currently they store a smaller amount of energy than a battery does.
Ultracapacitors are very good at efficiently capturing electricity from regenerative braking, and can deliver power for acceleration just as quickly. With no moving parts, they also have a very long lifespan - 500,000 plus charge/recharge cycles. Ultracapacitors are currently used for wind energy, solar energy, and hydro energy storage.


An ultra capacitor, also known as a double-layer capacitor, polarizes an electrolytic solution to store energy electro statically. Though it is an electrochemical device, no chemical reactions are involved in its energy storage mechanism. This mechanism is highly reversible, and allows the ultra capacitor to be charged and discharged hundreds of thousands of times.


Once the ultra capacitor is charged and energy stored, a load (the electric vehicle's motor) can use this energy. The amount of energy stored is very large compared to a standard capacitor because of the enormous surface area created by the porous carbon electrodes and the small charge separation created by the dielectric separator. Here is a very basic example of how an ultra capacitor works by using a circuit that uses a dc motor.






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