Method and apparatus for monitoring the condition of a battery by measuring its internal resistance

  • US 7,902,828 B2
  • Filed: 11/20/2007
  • Issued: 03/08/2011
  • Est. Priority Date: 02/17/2006
  • Status: Active Grant
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First Claim
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1. A method of monitoring the electric power of a battery by measuring an internal resistance of the battery, comprising the steps of:

  • (1) coupling a first power transistor across the two terminals of the battery to provide a first known external load, so as to draw a first transient current for a very transient sampling time, while measuring the voltage across the battery, thus obtaining a reference voltage;

    (2) coupling a second power transistor across the two terminals of the battery to provide a second known external load, so as to draw a second transient current for a very transient sampling time while the first load is still coupled across the two terminals of the battery, and while measuring the voltage across the battery, thus obtaining a load voltage, and measuring the second transient current; and

    (3) calculating the internal resistance of the battery by subtracting the load voltage from the reference voltage and dividing by the second transient current.

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