Abstract

An equalizer for equalizing the charge on several series-connected cells includes a transformer having plural windings on a core corresponding to the number of cells. The windings are tightly coupled to one another. A switching device such as a MOSFET is connected to each of the windings, and a winding and a switching device are connected across each of the cells. The switching devices are simultaneously switched at a relatively high frequency, e.g., 20 Hz, and the voltage across the highest charged cell appears across each of the windings when the switching devices are on. Current flows from the most highly charged cell to a cell or to cells of lower charge, with the charging current being proportional to the difference in voltage between the highest charged cell and each of the lesser charged cells. Equalization is carried out with very little power consumption by the equalizer, allowing charging to take place in a rapid manner.

Other References

• Heribert Schmidt et al., "The Charge Equalizer--A New System to Extend Battery Lifetime In Photovoltaic Systems, U.P.S. and Electric Vehicles," 15th INTELEC Conference, Paris, France, 1993, pp. 146-151
• Stephen T. Hung, et al., "Extension of Battery Life via Charge Equalization Control," IEEE Transactions on Industrial Electronics, vol. 40, No. 1, Feb. 1993, pp. 96-104
• David Fouchard, Walter Ebner, Sid Megahed, "Development of a Lithium-Ion BB-2847 Battery," Proceedings of the 36th Power Sources Conf., Cherry Hill, NJ, Jun. 6-9, 1994, p. 69, et seq
• Sony Corporation Battery Group & Sony Energytec, "Development and Commercialization of Lithium Ion Secondary Batteries," JEC Battery Newsletter, No. 4, Jul.-Aug. 1993, pp. 19-23 (with additional copy of the drawing on p. 23)
• Communication from Linear Technology Corporation to Sid Megahed of Rayovac Corporation, entitled "Lithium Ion Battery Monitor," May 31, 199