A method for controlling wireless transmission of energy supplied to an electrically powered medical device (100) when implanted in a patient. The method comprises powering the medical device by an internal energy receiver (102) of the medical device and wirelessly supplying energy to the internal energy receiver by an external energy source (104) located externally to the patient. The external energy source is equipped with a primary coil (11) from which the external energy source inductively transmits said energy to a first secondary coil (10) in the energy receiver. The method further comprises determining, by measurements, one or more parameters related to a first coupling factor (C1) between the primary and the first secondary coil (10), transmitting, by the external energy source, a first amount of energy to the energy receiver for enabling detecting, by the medical device, information related to the first coupling factor and wirelessly sending feedback information related to said first coupling factor to the external energy source. The method further comprises receiving, by the external energy source, the feedback information from the medical device, performing, by the external energy source, a predetermined action based on said feedback information.
