Be Your Own Battery

A backpack converts human motion into electricity

Today’s tech-savvy soldier with night-vision goggles, radio and wearable computer is primarily battery-powered. Now biologist Lawrence Rome of the University of Pennsylvania has found a far better way to recharge the 21st-
century soldier-and civilian, for that matter.

The solution, funded by the U.S. Office of Naval Research and the National Institutes of Health, is a backpack that harnesses the up-and-down motion of the hips when a person walks and converts the mechanical energy into electricity. “I pulled my 30-year-old external-frame backpack out of my closet,” Rome says. Weighting the pack, he set it on springs so that it would bounce with each step and then coupled it to a generator. Carrying weights of between 44 and 84 pounds, testers generated up to 7.4 watts, more than enough to directly power a full flight of electronic gear or to recharge batteries as they die.

While Rome anticipates a two- to three-year review process by the Navy, he’s founded a company, Lightning Packs, to bring his invention to emergency workers within a year. (There’s already interest from the New York City fire department.) But the biggest customer may be the average camper: Setting the load on springs not only generates electricity, it makes the pack more ergonomic.

INSIDE THE POWER PACK

Backpack

Attached to an aluminum load plate, a nylon sack is free to slide up to three inches vertically along a pair of steel runners screwed to a five-pound aluminum pack frame. The load plate can accommodate up to 84 pounds of gear.

Motor

A geared DC motor spins at up to 5,000 rpm as the toothed rack slides up and down, producing as much as 7.4 watts of power, suitable for charging batteries or directly running electronic equipment.

Gear System

A steel-toothed rack extends several inches above the sack to meet the brass pinion gear of a motor that´s attached to the top of the pack frame. Three steel springs suspend the load plate from above, and one spring secures it from below. This setup optimizes the vertical movement of the sack on the wearer´s back.