It doesnt work that way in the real world, only on paper. It isnt a perfect conversion. After heat and friction that HP draw increases it quite a bit. If it only sucked that little amount of power at that current output their would be no reason for increasing idle speeds and you wouldnt feel the engine drag down so much when you used certain accessories like power windows, defrosters, and even the blower on high. All of those combined might draw half of that 57 amp per 1 horsepower rating from that formula. In fact, alternators are generally anywhere from 45-65% efficient, so a general rule of thumb is that an alternator will draw 1 horsepower per 25 amps. This is a generalization, because as output increases efficiency decreases.