Battery charging system and methods

1. A method for determining whether a battery is electrically and physically connected to a battery charger, said method comprising:

providing an electric device that includes a battery and a superimposed signal detector circuit;

connecting a battery charger to the electric device across at least one connector;

monitoring, using the superimposed signal detector circuit, a battery charging voltage supplied to the electric device across the at least one connector by the battery charger, wherein the battery charger has superimposed a known signal on the battery charging voltage using a shunt to reduce the battery charging voltage for a predetermined interval of time;

determining that the battery charger is connected when the known superimposed signal is present and that the battery charger is not connected when the known superimposed signal is absent; and

opening a switch upon detection of the known superimposed signal to enable executing an output.

2. A method in accordance with claim 1 wherein the electric device is a vehicle, said determination performed within the vehicle.

3. A method in accordance with claim 2 further comprising activating an indicator when it is determined that the battery charger is connected.

4. A method in accordance with claim 2 further comprising disabling a motor in the vehicle when the battery charger is connected.

5. A method in accordance with claim 2 wherein the at least one connector includes a cable having only two wires.

6. A method in accordance with claim 1 wherein the known superimposed signal comprises periodic pulses.

7. A method in accordance with claim 1 wherein said monitoring the battery charging voltage comprises filtering DC from the battery charging voltage.

8. A battery charger comprising:

a DC charging circuit configured to provide a DC charging voltage;

a signal superimposing circuit configured to superimpose a known signal on the DC charging voltage using a shunt to reduce the battery charging voltage for a predetermined interval of time;

at least one connector for connecting said battery charger to an electric device that includes a superimposed signal detector circuit, said battery charger configured to transmit the supcrimposed signal across said at least one connector to be detected by the superimposed signal detector circuit; and

a switch configured to open upon detection of the superimposed signal to enable execution of an output.

9. A battery charger in accordance with claim 8 wherein the signal superimposing circuit is a pulsed current shunt circuit.

10. A battery charger in accordance with claim 9 further comprising a timing circuit, and wherein the pulsed current shunt circuit generates pulses in accordance with the timing circuit.

11. A battery charger in accordance with claim 8 wherein said at least one connector comprises only two electrical wires.

12. A battery charger system comprising:

a battery charger comprising a DC charging circuit and a signal superimposing circuit;

a superimposed signal detector circuit positioned within an electric device including a chargeable battery; and

at least one connector connecting said battery charger to the electric device, said DC charging circuit configured to provide a battery charging voltage across said at least one connector to the electric device, said signal superimposing circuit configured to superimpose a known signal on the battery charging voltage using a shunt to reduce the battery charging voltage for a predetermined interval of time, said superimposed signal detector circuit configured to detect the known superimposed signal; and

a switch configured to open upon detection of the known superimposed signal, said switch further configured to signal that said battery charger is connected to the electric device and inhibit operation of the electric device when said battery charger is connected to the electric device.

13. A battery charging system in accordance with claim 12 wherein the electric device is a vehicle.

14. A battery charging system in accordance with claim 13 wherein said superimposed signal detector circuit is configured to activate an indicator when the presence of a battery charger connection is detected.

15. A battery charging system in accordance with claim 13 wherein the electric device includes a motor, wherein said superimposed signal detector circuit is configured to prevent the motor from operating when a presence of a battery charger connection is detected.

16. A battery charging system in accordance with claim 12 wherein the known superimposed signal comprises periodic pulses, said superimposed signal detector comprises a pulse detector.

17. A battery charging system in accordance with claim 16 further comprising a timing circuit configured to control the pulse detector to detect signals of known periodicity.

18. A battery charging system in accordance with claim 17 wherein said signal superimposing circuit comprises a pulsed current shunt.