Automotive alternator efficiency has become of a prime importance for the reduction of car's consumption. The paper shows the experimental repartition of various losses. It is shown that, especially for high speed operation, the iron losses become an important part of the total losses. These iron losses are very difficult to determine because classic models are not adapted. Concerning the stator losses, the flux density is not in the sheet plane, so classic Berttoti models may become inaccurate. Iron rotor losses are mainly due to the induced currents in the massive materials due to the modulation of the rotor stator permeance variation. In this paper, we propose, in a first part, to compare on the basis of experimental results, the variation of the iron losses as a function of the stator windings and in a second part, an estimation of the rotor iron losses by comparing 3D Finite element and experimental results.