MIT researchers extend computer life without batteries

Researchers replace batteries with ultracapacitors to make long-running PCs

Researchers at the Massachusetts Institute of Technology have found a way to extend the power life of mobile computers.

Instead of using batteries, they draw power from an electronic device called an ultracapacitor. The approach is still several years away from being used as the main electricity source for commercial laptops and handhelds, but is already used for backup power in many small consumer products.

"A number of electronic devices already use commercial ultracapacitors for specialized functions," said Joel Schindall, a professor in MIT's Department of Electrical Engineering and Computer Science, in Cambridge, Massachusetts.

"For example, a clock radio may use an ultracapacitor as a keep-alive source in case of power failure, and even the old Palm III used an ultracapacitor to retain its memory while the AA batteries were changed."

The new technology could shake up the retail computer business, where computer makers already compete for market share by boasting of more power-efficient machines.

Chip makers battle for business by launching more efficient processors like Intel's Centrino and Advanced Micro Devices' Turion, trading high performance speed for mobile endurance.

Hewlett-Packard Co. also says its customers demand longer run-times. The company announced Monday that its HP Compaq nx9400 notebook will run on three levels of battery packs. Those range from the standard, four-hour unit to a substitute battery that adds five more hours, and a clip-on, supplementary battery that adds another 10 hours.

The speed at which a battery charges is also important to users. HP says its enhanced, lithium ion battery can gain 90 percent of a full charge after just 90 minutes of being plugged into a wall outlet.

By comparison, a consumer with a cell phone powered by MIT's ultracapacitor could gain a complete recharge in just a few seconds, Schindall says.

The new device is called a nanotube-enhanced ultracapacitor, or NEU. It works by applying nanotechnology to an existing electrical device; the capacitor.

Generic capacitors store energy as an electrical field. That is more efficient than standard batteries, which get their energy from chemical reactions. Even more efficient is the ultracapacitor, a capacitor-based storage cell that provides quick bursts of instant energy. The drawback is size -- ultracapacitors need to be much larger than batteries to hold the same charge.

The MIT researchers solved this problem by taking advantage of the enormous surface area of nanotubes; molecular-scale straws of carbon atoms that enable ultracapacitors to store electrical fields at the atomic level. Storage capacity (and charging speed) in an ultracapacitor is proportional to the surface area of the electrodes, so the nanotubes provide a great leap forward.

Despite this promise, researchers say they still have three to five years more work before they can replace a computer's main battery.

One drawback is that the ultracapacitor provides direct current power. That is suitable for running power-off functions like a laptop's clock, but most desktop devices use alternating current for their main operations.

High cost could also be a problem at first, because of low quantity production and meager capital investment in manufacturing facilities, he said.

On the other hand, the device could clear these hurdles by finding customers across a variety of businesses. From cell phones to automobiles, the ultracapacitor could supplement fuel cell power sources by acting as an emergency reserve for peak power use.

"The eventual implications are profound," says Schindall.

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Ben Ames

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