Battery string performance measurement
A DC power supply system in which the resistance of a battery is measured. The voltage of the DC power supply is reduced such that the battery supplies some current to the load, and the voltage and current are measured. The voltage of the DC power supply is further reduced such that the battery supplies increased power to the load, and the voltage and current are measured. A resistance value is computed, and may be compared with various pre-established criteria. The battery resistance may also be measured by comparing the charging time of a known resistive-capacitive circuit with the charging time established at a prior measurement epoch.
1. A resistance measuring apparatus comprising:
a first voltmeter;
an ammeter;
a first terminal of the ammeter connected to a first terminal of a first voltmeter;
a second terminal of the first voltmeter connected to ground;
a second terminal of the ammeter connected to a first external connection terminal;
a second external connection terminal connected to ground;
an output terminal connected to the first terminal of the ammeter;
a DC power supply, the DC power supply connected to the first terminal of the ammeter; and
a controller configured to communicate with the DC power supply and control an output voltage of the DC power supply,
wherein the DC power supply is not a battery.
2. The apparatus of claim 1 , wherein a battery is connectable between the first external connection terminal and the second external connection terminal.
3. The apparatus of claim 2 , wherein the battery is a lead-acid battery.
4. The apparatus of claim 2 , wherein the battery further comprises a plurality of batteries connected in series.
5. A method of measuring resistance, the method comprising:
providing a DC power supply and an electrical load, connectable to a battery;
providing a controller for adjusting an output voltage of the DC power supply;
measuring a first voltage value and first current value when the DC power supply output voltage is adjusted to a first value such that a connected battery supplies the first current value;
measuring a second voltage value and a second current value when the DC power supply output voltage is adjusted to a second value, the second value being lower than the first value, such that the connected battery supplies the second current, wherein the second current value is greater than the first current value; and
calculating a battery resistance.
6. The method of claim 5 , further comprising controlling the DC power supply output voltage such that the output voltage is gradually reduced to a first voltage, and then reduced to a second voltage.
7. The method of claim 6 , wherein the output voltage is rapidly reduced to a second voltage.
8. The method of claim 5 , wherein the first current value is approximately half of a maximum current value.
9. The method of claim 8 , wherein the second current value is substantially the maximum current value.
10. A battery resistance measuring apparatus comprising:
an ammeter;
a switch, the switch having a first terminal selectably connectable to one of a second terminal and a third terminal;
a second terminal of the switch connectable to a first electrical load;
a third terminal of the switch connected to a second electrical load, the second electrical load having a controllable resistance value;
a first terminal of the ammeter connected to the first terminal of the switch;
a second terminal of the ammeter connected to a first battery connection terminal;
a second battery connection terminal connected to a ground; and
a voltmeter connected between the first terminal of the ammeter and the ground.
11. The apparatus of claim 10 , wherein the second electrical load is a resistor having a plurality of selectable values.
12. The apparatus of claim 10 , wherein a stored-program computer controls the switch, controls the resistance value of the second electrical load receives measurements of voltage and current, computes the resistance of the battery, and outputs the computed battery resistance.
13. The apparatus of claim 10 , wherein a stored-program computer controls the switch, controls the resistance value of the second electrical load measures the voltage and current voltmeter, computes the battery resistance and outputs the computed battery resistance.
14. An apparatus for measuring resistance, comprising:
a first battery connection terminal;
a second battery connection terminal connected to ground;
a first resistive divider comprising a first and a second resistor having a first node between a first end of each of the first and second resistors, a second end of the first resistor connected to the first battery connection terminal and a second end of the second resistor connected to ground;
a network having a second node between a first end of a third resistor and a first end of a capacitor, the first end of the third resistor connected to the first battery connection terminal and a second end of the capacitor connected to ground;
a voltage comparator having a first input connected to the first node and a second input connected to the second node; and
a first switch connected between the first battery connection terminal and an output terminal.
15. The apparatus of claim 14 , wherein a stored-program computer controls the first switch and the output of the voltage comparator, computes the battery resistance, and outputs the computed battery resistance.
16. The apparatus of claim 14 , wherein a second switch is disposed between the first end of third resistor and the second node.
17. The apparatus of claim 14 , wherein a second switch is disposed between a second end of the third resistor and the first battery connection terminal.
18. A method of measuring battery resistance, the method comprising:
connecting an input terminal to a resistive divider;
disconnecting the input terminal from an output terminal;
connecting the input terminal to an input of a resistive-capacitive circuit;
determining the time required for the voltage across the terminals of a capacitor of the resistive-capacitive network to become equal to the voltage at an output of the resistive divider; and
calculating a battery parameter.
19. The method of claim 18 , wherein the battery parameter is a resistance.
20. The apparatus of claim 1 , wherein an input of the DC power supply is connectable to a source of alternating current power.
21. The apparatus of claim 1 , wherein an input of the DC power supply is connectable to at least one of a backup electrical generator or a power distribution grid.
22. The apparatus of claim 1 , wherein an input of the DC power supply is connectable to a power distribution grid.
23. The apparatus of claim 1 , wherein the first terminal of the first voltmeter is connected to a third external terminal.
24. The apparatus of claim 23 , wherein the third terminal is connectable to an electrical load.