New Charging Algorithm can Extend Battery Life for Electric Vehicles
A new charging algorithm could extend battery life for the first all-electric, battery-powered locomotive in the US.
Batteries for Norfolk Southern Railway No. 999, just like automotive batteries, are rechargeable until they eventually die. A leading cause of damage and death in lead-acid batteries is sulfation, a degradation of the battery caused by frequent charging and discharging that creates an accumulation of lead sulfate.
Engineers increased the cell capacity of lead-acid batteries like those that power Norfolk Southern Railway No. 999 by 41 percent and the overall battery capacity by 30 percent. (Credit: Michael Bezilla/Penn State)
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In a recent study, the researchers looked for ways to improve regular battery management practices. The methods had to be non-destructive, simple, and cheap—using as few sensors, electronics, and supporting hardware as possible while still remaining effective at identifying and decreasing sulfation.
“We wanted to reverse the sulfation to rejuvenate the battery and bring it back to life,” says Christopher Rahn, professor of mechanical engineering at Penn State.
Rahn, along with mechanical engineering research assistants Ying Shi and Christopher Ferone, cycled a lead-acid battery for three months in the same way it would be used in a locomotive.
They used a process called electro-impedance spectroscopy and full charge/discharge to identify the main aging mechanisms. Through this, the researchers identified sulfation in one of the six battery cells.
They then designed a charging algorithm that could charge the battery and reduce sulfation, but was also able to stop charging before other forms of degradation occurred.
The algorithm successfully revived the dead cell and increased the overall capacity. The researchers, who report their results in the current issue of the Journal of Power Sources, then compared the battery to a new battery.
“We desulfated it, and we increased its capacity,” says Rahn. “We 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 researchers increased the cell capacity by 41 percent and the overall battery capacity by 30 percent. Even better results might have occurred if sulfation were the only aging mechanism at play, but the researchers found other factors reduced capacity, as well.
“Some of the other cells we identified may have had a water loss issue,” says Rahn. “And for these types of batteries, there’s nothing you can do about it.”
Other mechanisms that can damage lead-acid batteries include positive electrode corrosion, irreversible hard sulfation, positive electrode softening or shedding, electrolyte stratification, internal short-circuiting, and mechanical damage.
The researchers are now developing alternative models to replace the electroimpedance spectroscopy model that would allow charging right up to, but not past, sulfation in batteries where sulfation is not yet present, hoping to prevent it from occurring in the first place.
“You would charge as fast as you can and right when you see gassing starting to happen, you ramp down and reduce the current charging,” says Rahn. “It’s still related to degradation, but it’s not really a rejuvenation project anymore.”
Penn State and Norfolk Southern, which operates 21,000 route-miles in 22 states, began developing locomotive No. 999 in 2008 to evaluate the application of battery technologies for railroad motive power, with particular interest in energy savings and emissions reduction. The US Department of Energy funded the study.
By. Jennifer Swales
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