Battery float management

• US 20070080668A1
• Filed: 07/02/2004
• Published: 04/12/2007
• Est. Priority Date: 07/02/2003
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Industries Limited (Eaton Corporation PLC.)
• Inventors: Hunter, Phillip, Al-Anbuky, Adnan
• Granted Patent: US 7,772,851 B2
• Time in Patent Office: Days
• US Class Current: 320/136
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: H01M 10/121 Valve regulated lead acid batteries [VRLA]
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: H01M 10/4285 Testing apparatus
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• 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: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

The invention relates to a new VRLA battery float model. The model covers the steady state and transient float charge behaviour of both positive and negative electrodes. Backup analysis verifies the internal polarisation distribution for a conventional 2V-cell polarisation behaviours can be identified without the need for a physical reference electrode. The estimated individual electrode polarisation allows early detection of common failure modes like negative plate discharge as well as a reference for float voltage optimisation. Furthermore, the positive polarisation relating to minimum grid corrosion may be correlated with the occurrence of the peak of a “Tafel” like resistance used by the model. The model encourages utilisation of low signal perturbation for testing a cell'"'"'s state of health and state of charge conditions while at float.

Claims

1. A method for determining polarisation of an electrode of a VRLA battery, the method including the steps of:

allowing the battery to discharge for a selected period of time, monitoring the battery voltage during the selected period, and from the change in voltage over the selected period, determining the polarisation of the electrode.

2. A method as claimed in claim 1 including detecting the magnitude of the change in voltage to determine the polarisation of the electrode.

3. A method as claimed in claim 1 including the step of detecting a first change in battery voltage and a subsequent second change in battery voltage, and associating the first change with polarisation of a negative electrode and the second change with polarisation of a positive electrode.

4. A method as claimed in claim 3 including comparing the polarisation of at least one electrode with an expected polarisation value or range of polarisation values to determine parameters of a float charge to be applied to the battery.

5. A method as claimed in claim 1 wherein the step of discharging comprises open circuit charge leakage.

6. A method as claimed in claim 1 wherein the step of discharging comprises closed circuit enforced discharging.

7. A method as claimed in claim 1 wherein the step of discharging occurs as part of a current perturbation applied to the battery.

8. A method as claimed in claim 7 wherein the polarisation of the negative electrode is determined.

9. A method as claimed in claim 1 further including the step of using the difference between the battery voltage prior to discharge and the polarisation detected to determine the polarisation of the other electrode.

10. A method of providing a float charge to a VRLA battery, the method including the steps of:

allowing the battery to discharge for a selected period of time, monitoring the battery voltage during the selected period, and applying a float charge to the battery dependent on the change in battery voltage over the selected period.

11. A method as claimed in claim 10 wherein the step of discharging comprises open circuit charge leakage.

12. A method as claimed in claim 10 wherein the step of discharging comprises closed circuit enforced discharging.

13. A method of providing a float charge to a VRLA cell, the method including the steps of:

determining the peak Tafel equivalent resistance for the cell and applying a voltage to the cell electrodes dependent on the determined equivalent resistance.

14. A method of modelling a VRLA cell, the method including the steps of:

simulating a capacitance corresponding to a float region of cell operation of a positive electrode of the cell, simulating a capacitance corresponding to a float region of cell operation of a negative electrode of the cell.

15. A method as claimed in claim 14 wherein the capacitances are simulated as dual value capacitors, one value corresponding the bulk charge capacity of the cell and the other value corresponding to the float region.

16. A method as claimed in claim 14 including simulating a variable resistance for at least one electrode and varying the resistance to simulate a Tafel characteristic of the electrode.

17. A method of modelling a VRLA cell, the method including simulating a dual value capacitance, one value corresponding to a float region of cell operation and the other value corresponding to a bulk charge storage capacity of the cell.

18. A method as claimed in claim 17 including simulating a dual value capacitance in relation to a positive cell electrode and simulating a dual value capacitance in relation to a negative cell electrode.

19. Apparatus for providing a float charge to a VRLA battery, including a processing unit programmed to monitor the battery voltage during a selected discharge period for the battery, and determine a float charge to be applied to the battery dependent on the change in battery voltage over the selected period.

20. Apparatus for providing a float charge to a VRLA cell, including a processing unit programmed to determine the peak Tafel equivalent resistance for the cell and determine a voltage to be applied to the cell electrodes dependent on the determined equivalent resistance to provide the float charge.