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Battery charger with capacity monitor

  • US 5,410,239 A
  • Filed: 01/19/1993
  • Issued: 04/25/1995
  • Est. Priority Date: 04/03/1992
  • Status: Expired due to Fees
First Claim
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1. In an automatic shut-off charging system for charging a battery comprisinga DC power supply,a main switch connected in series between said DC power supply and the battery for selectively applying DC power for charging of said battery,a timing control circuit for intermittently interrupting the series connection between said DC power supply and said battery,and a comparison circuit for monitoring a reference voltage of said battery, said comparison circuit also being connected to said main switch for energizing said main switch when the reference voltage corresponds to a predetermined threshold, thereby removing said DC power for charging of said battery and disabling further charging when said battery is already fully charged, an improvement comprising:

  • a temporary load selectively connectable in parallel with said battery by means of a test switch to thereby establish the reference voltage indicative of an equivalent internal resistance of said battery, wherein said test switch is normally connected in series between said power supply and said battery, wherein said test switch is selectively energized by said timing control circuit at set time intervals to break the series connection between the DC power supply and said battery and to instead connect said temporary load in parallel with said battery, wherein said temporary load includes a series-connected resistance and capacitance, chosen in accordance with the equivalent internal resistance of said battery, wherein said comparison circuit is coupled in parallel across said resistance to monitor a peak value of the reference voltage falling across said resistance, and wherein said peak value of the reference voltage is indicative of a remaining charge capacity of said battery.

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