Process for determining the state of charge and the peak current loadability of batteries

• US 6,163,133 A
• Filed: 10/14/1999
• Issued: 12/19/2000
• Est. Priority Date: 10/15/1998
• Status: Expired due to Term

• Current Assignee: VB Autobatterie GmbH, Volkswagen AG
• Original Assignee: VB Autobatterie GmbH & Co. KGaA (Robert Bosch GmbH), Volkswagen AG
• Inventors: Meissner, Eberhard, Michels, Karsten, Laig-Horstebrock, Helmut, Dierker, Uwe, Ubermeier, Dieter
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/417,650
• Time in Patent Office: 432 Days
• Field of Search: 320/132, 320/130, 320/149, 320/DIG. 21, 324/432, 324/433, 324/430
• US Class Current: 320/132
• CPC Class Codes: G01R 31/3647 for determining the ability of a battery to perform a critical function, e.g. cranking
• CPC Class Codes: G01R 31/379 for lead-acid batteries
• CPC Class Codes: G01R 31/3835 involving only voltage measurements

Abstract

In a process for determining the state of charge and the peak current loadability of batteries in the currentless pauses before and after a loading phase the no-load voltages U₀₁ and U₀₂ are measured. From them, with allowance for battery-specific parameters, especially the time curve of the no-load voltage, the true battery rest voltages U₀₀₁ and U₀₀₂ are computed. During the loading phase the converted current quantity q is measured and from the relationship U₀₀₂ -U₀₀₁ =C₁ ·q/Q₀ the acid capacity Q₀ of the battery is found. The relative state of charge SOC₁ is determined from a curve of the rest voltage U₀₀ linearized by the formula SOC₁ =U₀₀₂ /C₁ -C₂ as a function of the state of charge of the battery from which the absolute state of charge is calculated as SOC₁ ·Q₀.

From the internal resistance R₁, a preassigned temperature and the last determined state of charge, a rest voltage is predicted for a later time from which, with the current necessary for starting the engine known, a pronouncement can be derived concerning the starting capacity of the battery.

Claims

1. A process for determining the state of charge and peak current loadability of a battery comprising:

measuring no-load voltages U₀₁ and U₀₂ in currentless pauses before and after a load phase;

calculating true battery rest voltages U₀₀₁ and U₀₀₂ from said no-load voltages U₀₁ and U₀₂ for battery specific parameters, including the time curve of the no-load voltage;

measuring the converted current quantity q, wherein q is the amount of capacity discharged during the loading phase;

determining the acid capacity Q₁₀ of the battery from the formula U₀₀₂ -U₀₀₁ =C₁ ·

q/Q₀ ;

determining the relative state of charge SOC₁ from a curve of the rest voltage U₀₀ linearized by the formula SOC₁ =U₀₀₂ /C₁ -C₂ as a function of the state of charge of the battery; and

calculating the absolute state of charge as SOC₁ ·

Q₀, wherein C₁ is a constant voltage and C₂ is a constant, both C₁ and C₂ depending on the number of cells in the battery.

2. The process of claim 1, wherein the measured rest voltage U₀, the voltage status, the time voltage curve and the duration of the rest pause are considered in calculating the true test voltage U₀₀.

3. The process of claim 1, wherein the measurement of the rest voltage U₀ during rest pauses occurs at fixed preassigned intervals.

4. The process of claim 1, wherein the calculated true rest voltage values U₀₀ are standardized by correction factors to a preassigned temperature.

5. The process of claim 1, wherein the true rest voltage U₀₀ is determined from measurements of the no-load voltage U₀ after a minimum resting time of about two hours.

6. The process of claim 1, wherein internal resistance R₁ is determined as a quotient of the differences of the voltages and the current before and during the peak current load.

7. The process of claim 1, wherein a rest voltage is calculated for a later time from which with the current known to be necessary for starting the engine a prediction can be derived concerning the starting capacity of the battery from the internal resistance R₁, a preassigned temperature and the last determined state of charge.

8. The process of claim 1, wherein C₁ is 1.5 V and C₂ is 7.5 for a six-cell battery.