Battery state of charge gauge

• US 4,595,880 A
• Filed: 08/08/1983
• Issued: 06/17/1986
• Est. Priority Date: 08/08/1983
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Motor Company
• Inventors: Patil, Prabhakar B.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/520,967
• Time in Patent Office: 1,044 Days
• Field of Search: 324/427, 324/428, 324/430, 324/431, 324/433, 324/434, 340/636, 320/48, 364/483
• US Class Current: 324/427
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

A method of computing the state of charge for a battery including the steps of sensing the battery voltage and current, and computing the used battery capacity, C_u, and the average battery current, I. The total battery capacity, C_t is calculated from average current using the Peukert equation. The state of charge is calculated as a function of C_u /C_t to account for temperature and aging effects, recuperation effects, regeneration effects, and current variation effects.

Claims

1. A method for computing the state of charge for a battery including the steps of:

measuring I_p, wherein Ip is the battery discharge current;

determining I, wherein I is the average battery current, by calculating ##EQU5## empirically determining k and n for the battery, wherein k and n are Puekert constants;

calculating the total capacity, C_t, of the battery using the Puekert equation, C_t =k·

Iⁿ ;

reevaluating k, n as a function of temperature and age of the battery;

calculating the used battery capacity, C_u, by integrating battery current with respect to time;

calculating the percent state of charge using (1-C_u /C_t) (100), and

repeating the above steps to determine the state of charge the battery at subsequent times.

2. A method as recited in claim 1 further comprising the steps of determining if the battery has gone through a charging-discharging cycle of between about eighty percent and forty percent of the maximum state of charge.

3. A method as recited in claim 2 wherein successive readings of battery current and temperature are made about 100 times per second and an average of the readings is taken about every second.

4. A method as recited in claim 3 wherein the effects of recuperation are taken into effect by detecting the occurrence of a zero battery current of about 300 seconds at which time recuperation is substantially completed.

5. A method for detecting in a battery an abnormal battery cell condition including the steps of:

measuring the battery voltage V, and current, I,;

calculating the used battery capacity, C_u, by integrating battery current with respect to time;

determining the partial derivative of battery voltage, V, with respect to used battery capacity, C_u ;

comparing dV/dC_u to a predetermined value; and

determining a battery cell has an undesirably high dynamic resistance if dV/dC_u is greater than the predetermined value.