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NREL - National Renewable Energy Laboratory
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2001 R&D 100 Award Winner

Current Interrupt Charging Algorithm for Lead-Acid Batteries

Developers: Matthew A. Keyser, Ahmad A. Pesaran, and Mark M. Mihalic, National Renewable Energy Laboratory; Robert F. Nelson, Recombination Technologies; Elizabeth D. Sexton and John Olson, Optima Batteries, Inc.

The current interrupt charging algorithm is a simple approach for recharging lead-acid batteries that extends the cycle life of the batteries by 300% to 400%. Lead-acid batteries used in electric vehicles have, up until now, lasted only about 150 to 200 deep discharge cycles. This is primarily because the batteries have been charged using a constant current and voltage. In contrast, NREL and its partners devised a new and much more efficient way to charge batteries. Their method involves applying a current to the battery for 5 seconds to overcharge the battery slightly, then interrupting the current for 5 seconds. This allows the battery to cool down and avoid going into the oxygen recombination cycle, which leads to early failure of the negative battery plate due to oxidation of sulfuric acid into sulfate. This technique not only extends the battery life to 700 deep discharge cycles, it obviates the need for a battery management system, lowering the cost of the entire system. This simple technique is a breakthrough for the use of lead-acid batteries in electric vehicles. Compared to other, high-end, battery materials being used or considered for electric vehicles, lead-acid batteries using this charging method are less expensive to buy, less expensive to recycle, and last as long or longer.