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Lithium polymer battery charger methods and apparatus
| Details |
Inventors: Merritt, Lauren V.; Teofilo, Vincent L.; Hollandsworth, Roger Paul; Rodriguez, Zaid B.; Lovgren, Jack G.;
Assignee: Lockheed Martin Corporation (Sunnyvale, CA)
Primary Examiner: Wong; Peter S.
Assistant Examiner: Toatley, Jr.; Gregory J.
Attorney, Agent or Firm: Feix & Feix
Lithium polymer battery charger methods for charging a plurality of equal charge point lithium polymer battery cells prevent overcharging of any cell, whether the cells are arranged in a series stack or are arranged in parallel. When the cells are connected in a series stack, a power supply is connected to the series stack to apply a charge current to the series stack. The state of charge of each cell in the stack is monitored. Information that the state of charge of any cell is approaching full charge is used to control the charge current and to prevent overcharging of any cell. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Lithium polymer battery cells are unforgiving of overcharge.
An overcharged lead acid battery will electrolyze some easily replaced water, and nickel-cadmium or metal-hydride batteries have voltages which stop rising at full charge; but the voltage of the lithium polymer battery cell continues to rise even while being overcharged.
FIG.
1 shows how the voltage of a lithium polymer battery rises quite distinctly at the end of charge.
Thus, as illustrated in FIG.
1, for a lithium polymer battery cell having a fully charged voltage of 4.
0 to 4.
5 volts, the voltage can rise to a voltage of about 4.
7 volts.
See the overcharge area peak indicated by the reference numeral 11 in FIG.
1.
What is unique in the lithium polymer battery cell art is that lithium polymer battery cells won't stand such overcharging.
The overcharging must be avoided.
Overcharging damages the battery seriously.
There is no liquid to vaporize (as there is in a lead acid battery, for example).
Lithium polymer batteries work on the idea that lithium ions are embedded in a solid polymer.
The lithium polymer battery cell is a solid battery.
Overcharging can be visualized as depleting all of the lithium ions off of the plate.
Breaking connection by overcharging results in a condition in which there is no way to re-establish the connection.
It is essential to avoid overcharging of a lithium polymer battery cell.
The lithium polymer battery charger methods and apparatus of the present invention, as will be described in more detail below with reference to FIGS.
2-4, prevent overcharging of any cell, whether the cells are arranged in a series stack or are arranged in parallel.
FIG.
2 is a schematic diagram illustrating a lithium polymer battery charger 10 constructed in accordance with one embodiment of the present invention.
In FIG.
2 the lithium polymer battery cells to be charged are indicated by the reference numerals 13, 15, 17, and 19.
Each cell is to be charged from a voltage as low as the 2
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Electrical and Wave 
