Method and apparatus to detect leakage current between power sources

1. A method of detecting a leakage current between two electrical energy sources in a vehicle, the method comprising:

connecting a first voltage divider having a first center node, between the first power source and a reference potential for the vehicle;

determining a first voltage at said first center node;

connecting a second voltage divider having a second center node across the second power source;

connecting the second center node and the first center node to each other;

determining a second voltage at said first center node responsive to the connection of the second center node to the first center node, the second voltage being determined relative to the reference potential; and

determining whether the first and second voltages are unequal;

whereby unequal first and second voltages indicates a leakage current flowing from said second power source to at least one of the first power source and said reference potential.

2. The method of claim 1 , wherein the first and second power sources are batteries.

3. The method of claim 2 , wherein the two batteries have first and second different output voltages.

4. The method of claim 3 , wherein the second battery comprises a plurality of batteries connect together in series.

5. The method of claim 2 , wherein the second battery is configured to be electrically isolated from a ground potential but wherein a leakage current from said second battery flows from the second battery to said ground potential.

6. The method of claim 2 , wherein the step of connecting a first voltage divider comprises connecting to the first battery, a voltage divider having a voltage division factor of about two.

7. The method of claim 1 , wherein the step of determining whether the first and second voltages are unequal includes the steps of:

converting the first voltage to a first digital value;

converting the second voltage to a second digital value; and

computing a difference between the first digital value and the second digital value.

8. An apparatus for detecting a leakage current conducted between two electrical energy sources in a vehicle having a chassis, which carries a reference potential voltage, the apparatus comprising:

a first voltage divider having a first center node, the first voltage connected across a first, low-voltage power source and a reference potential for a vehicle;

a second voltage divider having a second center node, and which is connected across a second power source, which is electrically isolated from the first power source;

a switch, configured to provide a removable connection between the first center node and the second center node;

a processor, configured to be selectably coupled to the first center node when the switch is in a first position and coupled to the connection between the first center node and the second center node when the switch is in a second position, the processor being additionally configured to determine a first voltage when the switch is in the first position and determine a second voltage when the switch is in the second position and further configured to determine a difference between the first and second voltages.

9. The apparatus of claim 8 , wherein the first power source is a first battery having positive and negative terminals, the negative terminal of which is connected to the vehicle chassis.

10. The apparatus of claim 9 , wherein the second power source is a second battery comprising a plurality of separate cells.

11. The apparatus of claim 10 , wherein the second battery has positive and negative terminals, both of which are isolated from the vehicle chassis during normal operation of said second battery.

12. The apparatus of claim 8 , wherein the second voltage divider comprises first and second resistances, each resistance having a value of at least one million Ohms.

13. The apparatus of claim 8 , wherein the first voltage divider comprises first and second resistances having values which are substantially equal to each other.

14. An apparatus for detecting a leakage current between two batteries in a vehicle, the apparatus comprising:

a processor;

a switch, operatively coupled to and controlled by the processor and operatively coupled between first and second voltage dividers, which are selectably attachable to the first and second batteries; and

a non-volatile memory device coupled to the processor and storing program instructions, which when executed cause the processor to:

connect the first voltage divider having a first center node, between the first battery and a reference potential for the vehicle;

determine a first voltage at said first center node;

connect the second voltage divider having a second center node across the second battery;

connect the second center node and the first center node to each other;

determine a second voltage at said first center node responsive to the connection of the second center node to the first center node through actuation of the switch, the second voltage being determined relative to the reference potential; and

determining whether the first and second voltages are unequal.

15. The apparatus of claim 14 , wherein the program instructions cause the processor to identify unequal first and second voltages as indicative of a leakage current flowing from said second battery to at least one of the first battery and said reference potential.