Patent ID: 8620484

Claim:
A method of controlling inductive power transfer in an inductive power transfer system, the system including a primary unit, having a tank circuit and switching circuit, 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 a characteristic of input power in the primary unit; measuring a characteristic of power in the tank circuit of the primary unit; receiving, in the primary unit, information from the at least one secondary device; estimating power consumption in the inductive power transfer system as a function of at least the measured characteristic of power in the tank circuit of the primary unit; comparing the measured characteristic of input power in the primary unit, the information from the at least one secondary device, and the estimated power consumption to determine there is an unacceptable amount of parasitic metal present in proximity to the primary unit; and restricting or stopping the inductive power transfer from the primary unit in response to a determination that the unacceptable amount of parasitic metal is present in proximity to the primary unit.