This research paper investigate the use of an automotive alternator on an experimental stand to evaluate the capacity to load the battery and producing electricity for car systems. The efficiency was calculated by measuring the electric power supplied to the battery for different regimes of speed. Various aspects regarding the efficiency of energy conversion by using alternator was also discussed. The stand use an electric motor with various transmission rapports to rotate the alternator. The speed was recorded with a digital tachometer and the energy consumption of the electric motor with a digital wattmeter. The results obtained showed that the increase of alternator speed generate more electricity and better load of the battery.