Choosing an electric motor to replace a gasoline engine can be confusing because they deliver power in very different ways. A gas engine has a peak output related for its rpm, torque, and resulting horsepower. An electric motor is more of a moving target, since it generates more torque as it’s loaded, and draws more current as needed. The rating standards are considerably different, making it difficult to translate between the two types.
Our tiller’s plug-in AC motor runs on standard 120 VAC, and most household circuits have a 15 A breaker. If we overload the motor, it will draw more current, and eventually trip the breaker. After a trip down a long extension cord and topping out at 15 A, 120 VAC probably gives about 1,200 W at the motor (including inefficiencies and voltage drop). That converts to about 1.5 hp—the maximum actual horsepower delivered.
If you can’t deliver more than 1.5 hp to the tool, it’s pointless to use a motor rated any higher than that. If you need a larger motor, run a 240 VAC motor and electrical circuit.