You have two motors, one being 1.5HP and the other being 3HP. All other ratings are the same (e.g. motor efficiency ratings).
You attach a load to each motor. The load on each motor is identical at any given point in time. This load will range from no load to some stall load (obviously the stall load would be greater with the 3HP motor).
So for example, no load on each, take reading (how much power draw), add load, take reading of power draw, add more load, take reading of power draw...all the way to stall load...take power reading.
My question is, up until the smaller motor stalls, will the larger motor ever consume less power? Same goes for say a 2HP vs a 1.5HP. Can someone point me to the formula for doing this type of calculation?