Battery state-of-charge indicator

• US 3,886,442 A
• Filed: 04/12/1974
• Issued: 05/27/1975
• Est. Priority Date: 04/16/1973
• Status: Expired due to Term

• Current Assignee: Mikio Huruhashi, Shin Yamamoto, Takewo Chiku
• Original Assignee: Mikio Huruhashi, Shin Yamamoto, Takewo Chiku
• Inventors: Yamamoto, Shin, Huruhashi, Mikio, Chiku, Takewo
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/460,466
• Time in Patent Office: 410 Days
• Field of Search: 324/29.5 320/19
• US Class Current: 324/427
• CPC Class Codes: G01R 31/3646 for indicating electrical conditions or variables, e.g. visual or audible indicators
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3832 without measurement of battery voltage
• CPC Class Codes: G01R 31/3833 using analog integrators, e.g. coulomb-meters
• CPC Class Codes: Y10S 320/21 State of charge of battery

Abstract

A battery state-of-charge indicator to accurately measure and indicate the actual state-of-charge of a secondary battery, which comprises a compensation circuit for converting a discharging current of the battery to a compensated current substantially satisfying an equation I mIBn and an integrator for storing an ampere-hour corresponding with the known fully charged capacity of the battery and detecting a difference between an ampere-hour integrated therein from the compensated current and the stored ampere-hour to read the actual state-of-charge of the battery. In the above-equation, the characters I and IB are the compensated current and the discharging current respectively and the constants m and n are experimentally defined by the changes of the known fully charged battery capacity in relation to the changes of the discharging current to satisfy Peukert Equation.

Claims

1. An actual state-of-charge indicator for a secondary battery comprising:

a detecting means for detecting a discharging current exerting within an electric load circuit driven by said battery;

a compensation means for converting the discharginG current to a compensated current substantially satisfying an equation I mIBn, the characters I and IB being the compensated current and the discharging current respectively, and the constants m and n being experimentally defined by the changes of the known fully charged capacity of said battery in relation to the changes of the discharging current to satisfy Peukert Equation;

an integration means for storing an ampere-hour corresponding with said known fully charged battery capacity therein and detecting an actual state-of-charge of said battery by means of a difference between an ampere-hour integrated therein from said compensated current and said stored ampere-hour; and

an indicating means for reading said actual state-of-charge of said battery.

2. An actual state-of-charge indicator as claimed in claim 1, further including a thermo-compensation means for controlling said compensated current in accordance with the temperature changes of said battery.

3. An actual state-of-charge indicator as claimed in claim 1, further including a thermo-compensation means for controlling in accordance with the temperature changes of said battery said discharging current to be compensated by said first-named compensation means.

4. An actual state-of-charge indicator as claimed in claim 1, wherein said detecting means is a shunt resistor connected with said battery within said electric load circuit.

5. An actual state-of-charge indicator as claimed in claim 4, wherein said compensation means comprises a plurality of bias resistors for controlling a voltage appearing in said shunt resistor, a plurality of diodes connected respectively with said bias resistors to selectively be conducted in accordance with the rated bias resistances of said bias resistors in respect with the value of said voltage, said rated bias resistances being defined to satisfy said equation of I mIBn, and an operational amplifier for amplifying said voltage applied thereto across said diodes conducted selectively to be applied to said integration means.

6. An actual state-of-charge indicator as claimed in claim 5, wherein said integration means is provided with a second resistor for regulating the output of said operational amplifier, the rated resistance of said second resistor being defined in accordance with the rated value of said shunt resistor.

7. An actual state-of-charge indicator as claimed in claim 4, wherein said compensation means comprises a resistor for controlling a voltage appearing in said shunt resistor to be applied to said integration means, and a voltage dividing means for dividing said voltage in a predetermined ratio satisfying said equation of I mIBn, the divided voltage being additionally applied to said integration means.

8. An actual state-of-charge indicator as claimed in claim 1, wherein said integration means is a potential memory element having a solid electrolyte, an anode deposited on one surface of said electrolyte, and a cathode and a reference electrode deposited on the other surface of said electrolyte, said memory element storing an ampere-hour corresponding with said known fully charged battery capacity on said cathode and integrating said compensated current therein to detect a difference between an ampere-hour corresponding with said compensated current and said stored ampere-hour.

9. An actual state-of-charge indicator as claimed in claim 8, wherein said potential memory element is provided with an auxiliary battery to preliminarily store on said cathode an ampere-hour coresponding with said known fully charged battery capacity.

10. An actual state-of-charge indicator as claimed in claim 2, wherein said thermo-compensation means is a thermistor interposed between the output of said first-named compensation means and the input of said integration means.