How much more horsepower does it take to turn a high amp alternator over a lower amp one? The reason for the question is due to a test I recently did. I'm using a 1/3 horsepower electric motor on my test, when checking voltage output with a 37 amp compared to a 50 amp alternator, the 50 amp kills the 1/3 HP motor. I can't seem to get the video to load on here so go to youtube, type in, detrick 50 amp alternator and then, detrick 37 amp alternator to see the difference between the two. Wonder what a 100 amp would do?