Engineers at Pennsylvania State University in University Park wrote a new energy-reviving algorithm for lead-acid batteries that power an electric locomotive hauling freight for Norfolk Southern Railway. The team led by Penn State mechanical engineering professor Christopher Rahn describe their research, funded by Department of Energy, in this month’s issue of Journal of Power Sources (paid subscription required).
Norfolk Southern Railway No. 999 (pictured left) is the first all-electric, battery-powered locomotive in the U.S., operating some 21,000 route-miles in 22 states. No. 999 runs on 1,000 lead-acid batteries, like the ones found in standard internal-combustion automobiles. While the locomotive’s batteries are rechargeable, the frequent charging and recharging causes an accumulation of lead sulfate, a process called sulfation that can quickly degrade the battery and make it unworkable.
The research team, including research assistants and co-authors Ying Shi and Christopher Ferone, investigated ways of improving battery management on the locomotive, identifying nondestructive, simple, and inexpensive practices that Norfolk Southern could implement. The new methods, for example, had to limit the number of new sensors and other hardware, while still locating and reducing build-ups of lead sulfate. “We wanted to reverse the sulfation to rejuvenate the battery and bring it back to life,” says Rahn.
The Penn State team cycled a lead-acid battery for three months in the same way it would be used in a locomotive, with a process called electroimpedance spectroscopy and full charge/discharge to identify the battery’s main aging mechanisms. Through this analysis Rahn and colleagues found sulfation in one of the battery’s six cells.
The engineers designed a charging algorithm that would both recharge the battery and reduce sulfation. The algorithm also made it possible to stop charging the battery before other forms of degradation occurred. The team then ran the algorithm on the test battery and compared it to a new model.
The researchers found the algorithm successfully revived the dead battery cell, increasing the cell’s capacity by 41 percent and the battery’s overall capacity by 30 percent. “We desulfated it, and we increased its capacity,” says Rahn, adding that he and his colleagues “didn’t increase it all the way to brand new. We weren’t able to do that, but we did get a big boost.”
The Penn State team is now investigating a different process for analyzing lead-acid battery life other than electroimpedance spectroscopy that would allow a battery to recharge up to, but not past the point sulfation begins to occur, to prevent the lead sulfate build-up from occuring in the first place. “You would charge as fast as you can and right when you see gassing starting to happen,” says Rahn, “you ramp down and reduce the current charging.”
Sulfation, the researchers note however, is only one factor that can degrade a lead-acid battery. The Penn State team also found water loss, positive electrode corrosion, irreversible hard sulfation, positive electrode softening or shedding, electrolyte stratification, internal short-circuiting, and mechanical damage can also damage these batteries.
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