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Build Your Own Elec tric Vehicle so many years. There is no waiting, as with an internal combustion engine, while it winds up to its peak torque rpm range. Apply electric current to it and you’ve instantly got torque to spare. If any EV’s performance is wimpy, it’s due to a poor design or electric motor selection—not the electric motor itself. • Electric motors are inherently efficient. You can expect to get 90 percent or more electrical energy you put into an electric motor out of it in the form of mechanical torque. Few other mechanical devices even come close to this efficiency.
Horsepower Since electric motors are efficient, the horsepower behind them in a real electric car can be shocking to the system initially (no pun intended). I just remember the first time I drove an electric car. When I stepped on that accelerator it took off! No questions asked. No engine with excessive parts to get in the way of that. Here are some technical points to understand when trying to find the right motor for your car.
1. Electric motors are rated at their point of maximum efficiency; they may be capable of 2–4 times their continuous rating but only for a few minutes (acceleration or hill climbing). Internal combustion engines are rated at the peak horsepower. For example, the FB1-4001A motor is rated as 30 hp continuous at 144V and 100 hp peak. The 5-minute rating of the FB1-4001A motor is 48 hp at 144V.
2. Each 1,000 lbs. of vehicle weight after conversion requires 6–8 hp. This is the continuous rating of the motor. So a 3,000-lb. conversion requires a motor that is rated at approximately 20 hp. More horsepower is required for higher speeds, heavier vehicles, and steeper terrains.
3. The available horsepower of a motor increases with voltage; for example, the FB1-4001A motor is rated at 18 hp continuous at 72V but is rated at 30 hp continuous at 144V. As the voltage is increased the rpm increases. Horsepower is a function of rpm 3 torque.
4. Although electric motors are rated as “continuous,” the motor can run at less horsepower. If only 10 hp is required for the speed then the motor runs at that reduced load. This is the function of the motor controller.
5. Operating continuously above the rated horsepower will eventually overheat and damage the motor. A motor that is rated at 150 amps can run at 300 amps for a short time (minutes), but longer periods can easily damage the motor. Do not buy an undersize motor for your vehicle for your application—it will not last long. Current is what overheats components.
6. Highway speeds require greater horsepower. The horsepower required at 70 mph is four times the horsepower required at 35 mph. That means the current required is four times also, which means less range.
Depending on your design and component choices, the electric motor in your EV conversion can smoke its tires and routinely offer 60-mile range on a dollar’s worth of electricity. Compare that to 75 cents per mile in a hydrogen FC car, just for the “fuel” alone (of course, that’s beside the point, but hydrogen isn’t a fuel per se).
