A regulator system for modulating a field current of an alternator device, comprises logic arranged to receive or generate a reference signal comparison logic arranged to compare a received alternator output indication to the reference signal; and generate a field current modulation signal at least partially based on the comparison of the received alternator output indication and the reference signal. The regulator system further comprises logic arranged to receive at least one temperature indication. The regulator system comprises thermal compensation logic arranged to determine whether an indicated temperature exceeds at least a first threshold, and upon determining that the indicated temperature exceeds at least the first threshold, to apply compensation to the reference signal, the amount by which the reference signal is compensated is at least partly dependant on the amount by which the indicated temperature exceeds the first threshold.