Battery charging using a transformer with a single primary winding and plural secondary windings

A charging system for charging a string of two or more energy storage cells connected in series, and for equalizing the charge on the energy storage cells, comprising:

• (a) a bulk charging system having an input adapted to be connected to a source of AC power and an output adapted to be connected across the string of energy storage cells for applying a bulk DC charge voltage across the string of energy storage cells;
• and
• (b) a charge equalizer circuit including a transformer having a single primary winding and plural secondary windings wherein each secondary winding is adapted to be connected to a one of the energy storage cells, a power conversion means for applying a charge equalization voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells, and means for increasing a magnitude of the charge equalization voltage signal as the charge on the energy storage cells becomes equalized.

A charge equalizer for equalizing the charge on two or more energy storage cells connected in series, comprising:

• (a) a coaxial winding transformer having a single primary winding and plural secondary windings, wherein each secondary winding is adapted to be connected to a one of the energy storage cells, and wherein the coaxial winding transformer includes plural coaxial cables corresponding to the number of secondary windings and which are wound around a transformer core, wherein each coaxial cable includes an outer conductor and an inner conductor completely enclosed in the outer conductor, and wherein the outer conductors are connected in parallel to form the transformer primary winding and each inner conductor forms a transformer secondary winding;
• and
• (b) power converter means for applying an equalization voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells.