Electronic battery tester

• US 20020163338A1
• Filed: 05/10/2002
• Published: 11/07/2002
• Est. Priority Date: 01/13/1997
• Status: Active Grant

• Current Assignee: Kevin I. Bertness
• Original Assignee: Kevin I. Bertness
• Inventors: Bertness, Kevin I.
• Granted Patent: US 6,534,993 B2
• Time in Patent Office: Days
• US Class Current: 324/433
• CPC Class Codes: G01R 31/36 Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• 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

Abstract

A microprocessor couples to a voltage sensor through an analog to digital converter. The voltage sensor is adapted to be coupled across terminals of a battery. A small current source is also provided and adapted to be coupled across the terminal to the battery. The current source is momentarily applied to the battery and the resulting change in voltage is monitored using the microprocessor. The microprocessor calculates battery conductance based upon the magnitude of the differential current and the change in voltage and thereby determines the condition of the battery.

Claims

1. An apparatus for measuring conductance of a battery, comprising:

a positive sense electrical connection adapted to couple to a positive terminal of the battery;

a negative sense electrical connection adapted to couple to a negative terminal of the battery;

a positive current electrical connection adapted to couple to the positive terminal of the battery;

a negative current electrical connection adapted to couple to the negative terminal of the battery;

a current source;

a current switch selectively coupling the current source between the positive current electrical connection and the negative current electrical connection;

a first capacitor connected in series with the positive sense electrical connection;

a second capacitor connected in series with the negative sense electrical connection;

a differential amplifier having a first input, a second input and a differential output;

a first switch selectively coupling the first input of the differential amplifier to the first capacitor;

a second switch selectively coupling the second input to the differential amplifier; and

control circuitry coupled to the current switch, the first switch and the second switch selectively supplying the current source to the battery by actuating the current switch and maintaining at least a momentary disconnection between the battery and the amplifier by closing the first and second switches;

the control circuitry responsively determining battery conductance as a function of differential current flow through the battery due to the applied and differential voltage drop across the battery based upon the differential output.

2. The apparatus of claim 1 wherein the current source comprises a resistance.

3. The apparatus of claim 1 wherein the control circuitry provides an output related to relative battery conductance as a function of the battery conductance and a reference battery conductance.

4. The apparatus of claim 1 including:

the third switch selectively coupling the first input of the differential amplifier to a reference; and

wherein the control circuitry actuates the third switch to, momentarily couple the first input of the differential amplifier to the reference prior to determining battery conductance.

5. The apparatus of claim 1 wherein the control circuitry determines battery voltage prior to measuring current flow (V₁), during a measurement of current flow (V_M) and subsequent to measuring current flow and calculates change in voltage (Δ

V) as a function of V₁, V_M and V₂.

6. The apparatus of claim 5 including a first sample and hold circuit for sampling V₁, a second sample and hold circuit for sampling V_M and a third sample and hold circuit for sampling V₂.

7. The apparatus of claim 1 wherein the control circuitry subtracts an offset voltage in determining differential voltage drop.

8. The apparatus of claim 7 wherein the offset voltage is measured prior to determining battery conductance.

9. The apparatus of claim 1 including a memory and wherein the control circuitry compensates battery conductance as a function of an equation stored in the memory.

10. The apparatus of claim 9 wherein the equation comprises a polynomial of the form:

11. The apparatus of claim 1 wherein the control circuitry determines battery conductance as a statistical function of a plurality of differential current flow measurements and differential voltage measurements.