This might be a little thick for some of you, but I'll try to keep it simple. One thing that we have been hearing about electric cars since the beginning is that when you stop, the electrical system saves that energy rather than turning it into heat like regular cars do. Sounds good and it is technically possible. There are a lot of things that are possible, but there are very few that are practical or economical. I think you know the story that we can get power from the sun, wind and even the waves in the ocean. All true, but you and your kids would starve if you had to depend on those. Now back to one of my favorites, electric cars. I don't have a real problem with electric cars or electric golf carts. My problem is when the promoters make out landish claims about them.
Take this business about regenerative brakes. Here again, it is possible, but there are some problems with the concept. When you apply the brakes, you want the car to stop. With mechanical brakes like disc or shoe brakes, the kinetic energy of the car is transferred into frictional heat. That is why your brakes get hot, very hot. After you stop or stop using your brakes, they cool off transferring the heat to the atmosphere. Some big trucks run water on their brake drums to help get rid of the heat faster. With me so far?
Now let's take an example. We have a car that weights 3,000#, an average size car. Even the little electric cars are heavy because they have to carry that big battery. If we want to stop from 60 mph, the friction between the tires and the road will be the limiting factor by not having a coefficient of friction grater than about 0.5. That means the tires will slip if the stopping force is more than 50% of the weight of the car. That works out to 1,500# or 1/2 G. With a force of 1/2 G, and the car going 88 ft/sec, it will take 5.5 sec to stop the car. Sounds good. Now the kinetic energy of the 3,000# car at 60 mph or 88 ft/sec works out to be 66,000 (#ft**2)/sec**2. A little messie, but this works out to be equal to 122 hp. That means the car needs motors on the wheels that can generate a total of 122 hp. Wait, we are not done. Generating the energy is one thing, but putting it back into the battery is another thing. My prior calculations showed that the battery pack could only be recharged at the rate of about 11,000 watts and the brakes system is putting out over 8 times this amount. By my calculations, most of the kinetic energy is not going to be saved, it is going into heat just like standard disc brakes and is lost.
If you followed all this, you can do your own calculations and see what you come up with. My main point is that the car companies are playing fast and loose with technology because they know that most of us are dumb shits and won't know the difference. Our kids are even dumber and we are turning the future over to them. You figure?
