Why charge an electric car?

Question

When I was a kid the lights on my bike worked of a small generator rubbing front wheel. Why cant this be used to charge the battery system on a electric car? Only friction was where it made contact with tire to spin. Just wondering why

Answer 1

A spinning generator has no drag - until you try to take a load from it.

On a bike this is small & unnoticable compared to the effort moving the bike.

This is a very good example to help people understand power requirements:

Connect a 12V car dynamo or alternator to a stationary bicycle wheel. Then arrange car headlights that can be switched in, and see how many you can light, and experience how hard it is to pedal.

You are unlikely to produce 2 kW.

A car requires considerable more than this to accelerate.

and remember you can't get more energy out than you put in, aka perpetual motion, so a 5th wheel (or any other mechanism) would just introduce more drag than the energy it creates

Answer 2

Because the second law of thermodynamics says that even with very sophisticated energy recapture systems (such as regenerative braking) you will always lose some energy to heat and this must eventually be replaced.  Hybrid cars do this by burning gasoline (or diesel).  Pure electric cars will need to plug in to some source of electric power.

Answer 3

i really don't know? I think we should have that!

Answer 4

thats what an alternator on a car does exept its connected to the engine, not the wheels.  using dynamos on a cars wheels would never create enough energy to power the car, as energy is wasted as heat and the friction would slow the car down so it has to work harder

Answer 5

In some electic and hybrid vehicles the electric motors can be used to help in breaking the vehicle, this is known as regenerative breaking. It basicly turns the electic motos into generators which are then used to recharge the batteries. This can only recover a small portion of the charge used to operate the vehicle. Because no system is 100% efficient there will be losses due to heat and other components of loss. Therefore to keep the batteries charged fully you would have to recharge from an external source.

Answer 6

well that was only light , can u pedal a tonne or more? I mean that would be pretty funny to see people in rush hour traffic going 0.0076 miles an hour in business suits sweating there butts off

Answer 7

U can not get more out than u put in. It takes about 6 Hp. to Charge a car battery. Also there is loss when changing from mechanical force to electrical force. About 40% .

Answer 8

Modern hybrids use this technology, when braking the energy is returned by a generating system. Electric vehicles will always need some kind of power source because you cannot perpetually generate energy especially when some is being used to provide propulsion. The US patent office will not even accept applications for patenting a perpetual energy device since they violate the laws of physics.

When on your bicycle, your legs are the power source, the generator is only recapturing a small percentage of your energy.

Additional comment:

Okay, if you know so much then why did you come to this particular forum to ask a technical question only to attempt argument against answers that are actually based on facts?

Go build what you describe and prove us all wrong.. Believe me, people with much more training and experience in automotive design than any of us have already tried....it don't work.

BTW: Generaors have lots of resistance and drag. The generator in your average car takes  more horsepower to turn than the equivalent electricity it actually generates....it's physics man.

Answer 9

One of the laws of nature says that you can't get more out of a thing than you put in it. That battery on your bike didn't hold much energy, so it was easy to recharge it. The batteries in an electric car hold tens of thousands of watts, so it takes a lot of energy to charge them - much more than you could ever get from friction. And think about it - what would be pushing the car to drive the generator?