Universal inexpensive battery state-of-charge indicator

• US 5,372,898 A
• Filed: 02/17/1994
• Issued: 12/13/1994
• Est. Priority Date: 02/17/1994
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America), United States Department Of Health And Human Services
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Atwater, Terrill, Dratler, Richard M.
• Primary Examiner(s): Skapars, Anthony
• Application Number:
  US08/200,614
• Time in Patent Office: 299 Days
• Field of Search: 429/90, 429/91, 429/92, 429/93, 320/2, 320/29, 320/43, 320/48, 324/426, 324/439, 340/636, 340/700
• US Class Current: 429/90
• CPC Class Codes: G01R 29/24 Arrangements for measuring quantities of charge
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/3828 using current integration
• CPC Class Codes: H01M 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y10S 320/18 Indicator or display

Abstract

A discharge level monitor for a battery. The current flowing from the monred battery is passed through a sensing resistor. The voltage across the resistor is amplified and integrated over time and the result of the integration is stored in a capacitor. The capacitor is discharged by a switch controlled by a logic circuit, whenever a threshold voltage is achieved. The cycle is repeated each time one coulomb capacity is removed from the battery. A counting circuit counts the number of charge/discharge cycles of the capacitor to produce a count which is representative of the amount of energy dissipated and therefore indirectly of the amount of energy remaining in the battery system.

Claims

1. A battery system monitor, comprising:

a current sensing means for sensing current flowing from a battery to a load;

a current integrator for measuring the amount of electrical energy flowing from the battery and for producing an output indicative of a predetermined amount of electrical charge having been discharged from the battery;

a counter circuit for counting the output of the current integrator and for producing a counter output indicative of a discharge level of the battery; and

a display coupled to the counter circuit for providing a visual indication of the discharge level of the battery.

2. The battery system monitor of claim 1, wherein the current sensing means is tuned to compensate for variations in temperature and discharge rate.

3. The battery system monitor of claim 2, wherein the current sensing means is configured such that changes in temperature and discharge rate cause the current sensing means to time itself.

4. The battery system monitor of claim 2, wherein the current sensing means is tuned such that a threshold wattage represents a predetermined amount of capacity removed.

5. The battery system monitor of claim 1, wherein the current sensing means comprises a current sensing resistor of a very low value.

6. The battery system monitor of claim 5, wherein the current sensing resistor has a value below one ohm.

7. The battery system monitor of claim 5, wherein the current integrator is an operational amplifier and including a storage capacitor, the operational amplifier being effective to charge the capacitor at a rate approximately proportional to the current flowing through the resistor.

8. The battery system monitor of claim 7, wherein the current integrator further includes a differential amplifier and the differential amplifier is operative to discharge the capacitor when a predetermined amount of electrical energy has been stored therein.

9. The battery system monitor of claim 7, wherein the counter circuit includes a flip-flop circuit which is coupled to the counter circuit to assure that the counter circuit does not accidentally reset when a battery voltage associated with the battery has dropped below a predetermined value.

10. The battery system monitor of claim 7, wherein the display comprises a plurality of diodes and the state of the diodes is indicative of the discharge level of the battery.

11. The battery system monitor of claim 10, further including means for selectively enabling the display.

12. The battery system monitor of claim 7, further including switch means connected across input terminals of the battery system monitor and configured to be set to a conductive state to discharge the battery prior to the battery being disposed of.

13. The battery system monitor of claim 7, wherein the battery includes first and second batteries and including means of enabling connection of the first and second batteries to a load in either a series or a parallel configuration and wherein the current flowing through the first battery is monitored and the discharge level of the first battery is assumed for the second battery.