Patent ID: 7622891

Claim:
A primary unit, for use in a power transfer system that has a plurality of secondary devices, each said secondary device being separable from the primary unit and having a secondary coil adapted to couple with an electromagnetic field generated by the primary unit when the device is placed in a working disposition on or in proximity to a power transfer surface of the primary unit, so that power is transferred inductively from the primary unit to the secondary device, and the secondary devices differing from one another in one or more of a size of the device, a size of the secondary coil, and a power requirement of the device; said primary unit being adapted to transfer power inductively to each said device and comprising: a field generator having a plurality of nested coils of varying size for generating said electromagnetic field over the power transfer surface, the field generator also having an activator adapted to sense at least one of the size, the coil size, the power requirement, the position, and the rotation of the secondary device, the activator further adapted to selectively activate one or more of said nested coils in response to the sensing result to provide, at the power transfer surface, a power transfer area for transferring power inductively to the secondary device.