Multiple cell and serially connected rechargeable batteries and charging system

• US 5,821,733 A
• Filed: 12/16/1996
• Issued: 10/13/1998
• Est. Priority Date: 02/22/1994
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: Packard Bell NEC
• Inventors: Turnbull, Robert R.
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/767,170
• Time in Patent Office: 666 Days
• Field of Search: 320/2, 320/5, 320/6, 320/7, 320/15, 320/16, 320/17, 320/18, 320/110, 320/116, 320/118, 320/120, 320/121, 320/122
• US Class Current: 320/116
• CPC Class Codes: H01M 10/441 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H01M 10/46 Accumulators structurally combined with charging apparatus circuits for charging H02J7/00
• CPC Class Codes: H01M 50/213 adapted for cells having curved cross-section, e.g. round or elliptic H01M50/209, H01M50/216 take precedence
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/0042 characterised by the mechanical construction
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery charging system for multiple series connected battery cells which includes a plurality of shunt regulators, adapted to be connected in parallel with each of the cells. The voltage of each cell is monitored during charging. When a cell is fully charged, excess charging current is shunted around the fully charged cell to enable the remaining cells to continue to charge. Circuitry is also provided to prevent the charging system from discharging the cells when the battery is not being charged. In an alternative battery charging system, a voltage source is connected across each of the serially connected batteries. Each voltage source is capable of sourcing or sending charging current. During charging conditions, the voltage sources source charging current to the cells. In order to prevent fully charged cells from being overcharged, the voltage across each cell is monitored. When the cell becomes fully charged, as indicated by the cell voltage, excess charging current is sunk to ground. In another embodiment of the invention, a rechargeable battery, formed from multiple internally series connected cells is provided with an integral battery charger within the battery housing.

Claims

1. A battery charging system for charging a plurality of serially connected battery cells comprising:

means for providing charging current to said plurality of serially connected cells;

means for sensing the voltage across each of said serially connected cells;

means responsive to said sensing means for shunting the charging current around individual cells whose voltage is above a predetermined value; and

means for disconnecting said plurality of serially connected cells from said battery charging system to prevent substantially any discharge of said plurality of serially connected cells when said providing means is disconnected from said plurality of serially connected cells, said disconnecting means including one or more voltage activated electronic switches.

2. A battery charging system as recited in claim 1, wherein said sensing means includes differential amplifiers for comparing the voltage of each of the cells with a predetermined reference voltage.

3. A method for charging a plurality of serially connected battery cells comprising the steps of:

(a) providing a charging current to said cells;

(b) sensing the voltage across each of said cells;

(c) shunting the charging current around each cell whose voltage is greater than a predetermined value; and

(d) disconnecting said plurality of serially connected cells from said charging current using one or more voltage activated electronic switches to prevent substantially any discharge of said plurality of serially connected cells when said charring current is disconnected from said plurality of serially connected cells.

4. A battery charging system for a plurality of serially connected battery cells comprising:

means for sourcing charging current to each of said serially connected cells;

means for sensing the voltage across each of said serially connected cells;

means responsive to said sensing means for sinking current to ground around any cell whose voltage is above a predetermined value; and

means for disconnecting said plurality of serially connected cells from said battery charging system to prevent substantially any discharge of said plurality of serially connected cells when said providing means is disconnected from said plurality of serially connected cells, said disconnecting means including one or more voltage activated electronic switches.

5. A battery charging system as recited in claim 4, wherein said sensing means includes a plurality of differential amplifiers, each connected across the positive and negative terminals of each of the cells.

6. A battery charging system as recited in claim 4, wherein said electronic switches include a field effect transistor (FET).