A transcutaneous energy transfer system comprising: (a) an internal component adapted for mounting within the body of an animal, the internal component including: an internal coil; an internal device electrically connected to the internal coil for receipt of power from the internal coil; and a telemetry transmitter operative to send telemetry signals representing one or more parameters relating to operation of the internal component; and (b) an external component adapted for mounting outside of the body, the external component including: an external coil: a telemetry receiver adapted to receive the telemetry signals from the telemetry transmitter; a current monitor operative to measure current flow in the external coil and to provide an indication of whether or not the external coil is electromagnetically coupled to the internal coil based on the measured current flow; and a drive circuit operative in a normal mode of operation when the telemetry receiver receives the telemetry signals, and in a safe mode of operation when the telemetry receiver does not receive the telemetry signals, the circuit being operative to control power applied to the external coil at least in part responsive to the telemetry signals when operating in the normal mode; characterised by: the drive circuit being operative in both the normal and safe modes to apply power to the external coil so that power applied to the external coil will be coupled to the internal coil, said power being sufficient to operate the internal device. (a) an internal component adapted for mounting within the body of an animal, the internal component including: an internal coil; an internal device electrically connected to the internal coil for receipt of power from the internal coil; and a telemetry transmitter operative to send telemetry signals representing one or more parameters relating to operation of the internal component; and an internal coil; an internal device electrically connected to the internal coil for receipt of power from the internal coil; and a telemetry transmitter operative to send telemetry signals representing one or more parameters relating to operation of the internal component; and (b) an external component adapted for mounting outside of the body, the external component including: an external coil: a telemetry receiver adapted to receive the telemetry signals from the telemetry transmitter; a current monitor operative to measure current flow in the external coil and to provide an indication of whether or not the external coil is electromagnetically coupled to the internal coil based on the measured current flow; and a drive circuit operative in a normal mode of operation when the telemetry receiver receives the telemetry signals, and in a safe mode of operation when the telemetry receiver does not receive the telemetry signals, the circuit being operative to control power applied to the external coil at least in part responsive to the telemetry signals when operating in the normal mode; a telemetry receiver adapted to receive the telemetry signals from the telemetry transmitter; a current monitor operative to measure current flow in the external coil and to provide an indication of whether or not the external coil is electromagnetically coupled to the internal coil based on the measured current flow; and a drive circuit operative in a normal mode of operation when the telemetry receiver receives the telemetry signals, and in a safe mode of operation when the telemetry receiver does not receive the telemetry signals, the circuit being operative to control power applied to the external coil at least in part responsive to the telemetry signals when operating in the normal mode;