Method and device for determining characteristics of an unknown battery

Abstract

An apparatus for determining a rate of charge/discharge, C rate, or state of charge, SOC, of a battery having unknown characteristics comprises a circuit for applying at least a two-pulse current load to said battery. A change in voltage, ΔV, resulting from the application of the second or a subsequent pulse is used to determine the C rate of the battery as a function of ΔV. An Open Circuit Voltage, OCV, of the battery a time interval after the completion of the application of the second or subsequent pulse is used to determine the SOC of the battery as a function of OCV.

Description

DETAILED DESCRIPTION OF THE ART

FIG. 1 is a graphical representation of voltage and current against time for a battery having unknown characteristics to which a 20 Amp two-pulse load has been applied;

FIG. 2 is a graphical representation of characteristics of a 12V battery and a 6V battery with different C rates;

FIG. 3 is a graphical representation of ΔV against C rate for various battery sizes to which various different current pulse loads were applied;

FIG. 4 is a graphical representation of OCV against SOC for a variety of different battery sizes to which the same current load has been applied; and

FIG. 5 is a circuit schematic of a load circuit according to the preferred embodiment of the present invention.

Claims

1. A method of determining a rate of charge/discharge, C rate, of a battery having unknown characteristics comprising: applying at least a two-pulse current load to said battery;measuring a change in voltage, ΔV, only resulting from the application of one of the second or a subsequent pulse; anddetermining the C rate of the battery as a function of ΔV.

2. The method of claim 1 wherein said determining step comprises determining the C rate from a look-up table of values of ΔV.

3. The method of claim 1 wherein said determining step comprises determining the C rate as a mathematical function of ΔV.

4. The method of claim 1 further comprising determining a maximum capacity of the battery by dividing the applied current load by the determined C rate.

5. The method of claim 4 wherein the applied current load is a change in current from a first load current to a second load current and wherein said determining comprises determining a change in C rate as a function of said change in voltage.

6. The method of claim 1 further comprising: comparing ΔV with a benchmark; andchanging the value of the applied current load if ΔV does not comply with the benchmark.

7. The method of claim 6 wherein said benchmark comprises an upper limit and a lower limit.

8. The method of claim 7, comprising: responsive to ΔV being greater than the upper limit, decreasing the current load, andresponsive to ΔV being lower than the lower limit, increasing the current load.

9. The method of claim 1 comprising applying said current load pulse for an on-time of 10 secs and an off-time of 10 secs.

10. An apparatus for determining a rate of charge/discharge, C rate, of a battery having unknown characteristics comprising: a circuit for applying at least a two-pulse current load to said battery;a sensor for measuring a change in voltage, ΔV, only resulting from the application of one of the second or a subsequent pulse; andmeans for determining the C rate of the battery as a function of ΔV.