Drive it forever
Q. I have an idea to merge two technologies to develop a wind-generated electric car.
Here's how it would work: An electric car with charged batteries starts the vehicle moving. A wind generator is located in the engine bay, with the fan blades pointing down toward the road to reduce forward friction and drag. A funnel captures the air passing under the vehicle and flowing past the tips of the blades, perhaps in a cup shape, and out the back.
I keep getting comments that a three-blade generator will not produce enough watts. I have in mind something with more blades, such as a car alternator 2 to 3 feet in diameter. The unit would be sealed off under the engine bay, with only the blades exposed at the tips inside the funnel. Traveling at 60 miles an hour, with the wind passing under the vehicle, should produce a lot more wattage.
Once the car is moving, the wind flowing past the blades would generate power and keep the batteries charged. Once the batteries were charged, the generator would turn on and off as needed. This would most likely involve reduction gears, etc. If not fully self-powered, perhaps it could at least extend the current range of an electric vehicle.
I don't believe my idea is perpetual motion, which is defined as motion that continues indefinitely without any external source of energy and is impossible in practice because of friction. As most cars use gasoline as the external force for energy, my idea has the wind as power for the battery.
A. It's perpetual motion.
There is no real wind under or around a car. The "wind" you feel while driving comes from the car's forward motion through the air. That motion is the result of work done by the engine or motor, which is using energy from gasoline or electricity.
Adding your fan and generator to the system will increase the vehicle's aerodynamic drag, requiring more energy to be expended than you can recover from the generator.
It's the Second Law of Thermodynamics, and you can't get around it: Entropy always flows downhill. There are always losses in changing one form of energy into another.
Q. I installed a new battery in my car, which is not driven during the week, and a week later it died. How can the battery drain, even though it is parked all week? Could I have a faulty electric fuel pump that is draining the battery?
A. The only way the fuel pump could be draining the battery is if the pump were running full time - and, if that were the case, it would drain the battery within a few hours, not take a week.
A normal car battery has 48 to 64 ampere-hours of capacity, while a fuel pump draws 6 to 10 amps. Divide 64 by 6 and you get, at most, about eight hours before the battery would be too weak to start the car. A smaller battery or a pump that draws more current would lead the battery to run down even faster.
You may have a smaller parasitic drain, such as a light in the trunk or glove box that's not turning off.
Measure the battery current with all the accessories turned off by removing the ground clamp and putting an ammeter between the clamp and the post. You should see less than 50 milliamps of drain, which is normal. The computer's memory, the clock, and the radio draw this small amount of current, but that should take a month or two to drain the battery.
Are you charging this battery? Check that the battery voltage is more than 13.5 volts when the engine is running at fast idle. If not, the battery may not be getting charged properly, and you'll need to diagnose the charging system to find out why.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com. 