Patent ID: 8508077

Claim:
A method of controlling inductive power transfer in an inductive power transfer system, the system comprising a primary unit operable to generate an electromagnetic field and at least one secondary device, separate from the primary unit, and adapted to couple with the field when the secondary device is in proximity to the primary unit so that power is received inductively by the secondary device from the primary unit without direct electrical conductive contacts therebetween, the method comprising: measuring, in the secondary device or devices therefrom, a characteristic of a secondary power being supplied to a load of the secondary device; receiving, in the primary unit, power requirement information of the secondary device or devices therefrom, the power requirement information includes information relating to the measured characteristic of the secondary power; determining, in the primary unit, in dependence upon the power requirement information of the secondary device a power supplied to the secondary device or, if there is more than one secondary device, a combined power supplied to the secondary devices; measuring a primary power drawn from the primary unit, and determining if there is a substantial difference between the measured primary power and the power supplied; and following such determination of a substantial difference, restricting or stopping the inductive power supply from the primary unit.