BJ,

As the load (current demand) on a generator increases, more Counter-EMF (Electromotive Force) is developed, and it requires more force (horsepower) to overcome that greater Counter-EMF.

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.