| MadSci Network: Engineering |
Hello:
The answer to your first question: watts is a measure of work, same as horsepower. For DC motors it is simply the product of current times voltage. One horsepower equals 749 watts, so one hundred watts is the equivalent of (100/749) horsepower, an amount too small to power a 2000 lbs automobile. Any increase in voltage requires a decrease in the current to maintain the fixed amount of 100 watts.
Your second question requires knowledge beyond the weight of the car, that is, the parasitic drag associated with the car. Parasitic drag is the force required to overcome tire friction plus the aerodynamic drag. Aerodynamic drag for a well-designed car is negligible for speeds below 25 mph, but it becomes quite significant at 200 mph. Aerodynamic drag is not easy to estimate and requires access to a wind tunnel in order to be measured. Most auto makers and all Indianapolis car racers use wind tunnels to design or fine-tune their designs to minimize this parasitic force.
This also brings-up another question: 200 mph for how long? Just as your house is billed for electricity in kilowatt-hours, meaning thousands of watts used by the average time of one month, you will need to know how the capacity of the electric supply to predict how far or how long the auto could travel.
The first step taken by industry was to develop a hybrid propulsion system: a combination of battery power plus a small motor-generator running on conventional fuel. Visit this website: http://www.gmev.com/
The second step has been to develop a fuel cell. The fuel cell uses conventional fuel to directly generate electricity. Fuel cells are very expensive and my opinion is that it will require more technological refinement before it becomes a practical candidate to power electric cars.
Here is a list of websites where you can get additional information:
Electric Cars - Pulling the Plug
Fuel cell principles of operation
Fuel cell general characteristics
Aerodynamic Drag of Road Vehicles
Your MAD.SCI Micro.
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