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Research unveils ultracapacitor that delivers near-steady voltage

26 Jul 2012

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A researcher from the University of West Florida (UWF) has developed an ultracapacitor that can deliver energy at a near steady voltage. Ultracapacitors can deliver charges, and be recharged hundreds of thousands of times without degrading, but their voltage outputs drop as the device is discharged. According to Ezzat Bakhoum, a professor of electrical engineering at UWF, the latest development solves this issue, and may one day allow use of ultracapacitors in a wider range of applications such as low-voltage electric vehicle circuits and handheld electronics.

Standard capacitors store energy in an electric field created when opposite electrical charges collect on two plates separated by a thin insulating material. Ultracapacitors increase the surface area of the plates via a coating of porous activated carbon.

The space between the plates is filled with an electrolyte solution containing positive and negative ions. As charge accumulates on the plates, they attract ions, creating a double-layer of stored energy.

While DC/DC converters are a partial solution to the voltage drops experienced by ultracapacitors, a lot of the energy is held below one volt, which presents difficulties for the converters.

Bakhoum developed an ultracapacitor that maintains a near-constant voltage without a DC/DC converter.

The ultracapacitor is fitted with an electromechanical system that can slowly lift the core of the device out of the electrolyte solution as the stored charged is released. As the electrolyte drains away, the device can hold less charge, thus lowering its capacitance.

Since the voltage of the capacitor is related to the ratio of the stored charge to the capacitance, the system maintains a steady voltage as charge is siphoned off.

In a built prototype of the new ultracapacitor, Bakhoum found he could successfully program the voltage to stay within a 4.9V to 4.6V range. Testing also showed that the constant-voltage mechanism operates with 99 percent efficiency or higher.

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