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Ultra Capacitor

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column2-nrel-diagram_ultracapAn Ultra Capacitor is Electric double-layer capacitors (EDLC), also known as super capacitors, are electrochemical capacitors that have an unusually high energy density when compared to common capacitors, typically several orders of magnitude greater than a high-capacity electrolytic capacitor.
Generally, capacitors are constructed with a dielectric placed between opposed electrodes, functioning as capacitors by accumulating charges in the dielectric material. In a conventional capacitor, energy is stored by the removal of charge carriers, typically electrons from one metal plate and depositing them on another. This charge separation creates a potential between the two plates, which can be harnessed in an external circuit. The total energy stored in this fashion is a combination of the number of charges stored and the potential between the plates. The former is essentially a function of size and the material properties of the plates, while the latter is limited by the dielectric breakdown between the plates. Various materials can be inserted between the plates to allow higher voltages to be stored, leading to higher energy densities for any given size.

Screen Shot 2015-08-17 at 10.38.34 PMUltra Capacitors do not have any dielectrics in general, but rather utilize the phenomena typically referred to as the electric double layer. In the double layer, the effective thickness of the “dielectric” is exceedingly thin, and because of the porous nature of the carbon the surface area is extremely high, which translates to a very high capacitance. Generally, when two different phases come in contact with each other, positive and negative charges are set in array at the boundary. At every interface an array of charged particles and induced charges exist. This array is known as Electric Double Layer. The high capacitance of an Ultra capacitor arises from the charge stored at the interface by changing electric field between anode and cathodes.

Advantages:
• High energy storage. Compared to conventional capacitor technologies, EDLCs possesses orders of magnitude higher energy density. This is a result of using a porous activated carbon electrode to achieve a high surface area.
• Low Equivalent Series Resistance (ESR). Compared to batteries, EDLCs have a low internal resistance, hence providing high power density capability. • Low Temperature performance. Tecate Group PowerBurst® products, with their use of patented technology, are capable of delivering energy down to -40°C with minimal effect on efficiency.
• Fast charge/discharge. Since EDLCs achieve charging and discharging through the absorption and release of ions and coupled with its low ESR, high current charging and discharging is achievable without any damage to the parts.

Disadvantages:
• Low per cell voltage. EDLC cells have a typical voltage of 2.7V. Since, for most applications a higher voltage is needed, the cells have to be connected in series.
• Cannot be used in AC and high frequency circuits. Because of their time constant EDLCs are not suitable for use in AC or high frequency circuits.

Applications:

  1. Applications requiring a short duration power boost.
  2. In Low power,Capacitors are extensively used as power back-up for memory functions in a wide range of consumer products such as mobile phones, laptops and radio tuners.
  3. Super capacitors are also used to provide fast acting short term power back up for UPS applications. By combining a capacitor with a battery-based uninterruptible power supply system, the life of the batteries can be extended. The batteries provide power only during the longer interruptions, reducing the peak loads on the battery and permitting the use of smaller batteries.
  4. It is also used for energy storage for solar panels, and motor starters.
  5. Using super capacitors in EVs and HEVs to facilitate regenerative braking can add 15% to 25% to the range of the vehicle. At the same time, super capacitors can provide an effective short duration peak power boost allowing the prime battery to be downsized.

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