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-   -   Wind generator (https://www.askmehelpdesk.com/showthread.php?t=652644)

  • Apr 20, 2012, 06:41 AM
    7up
    Wind generator
    I was just wondering about something,could a wind generator be used on a electric vehicle to charge the batteries but with a cut off point so not to overcharge the batteries.also have a auto turn on when batteries get low.
  • Apr 20, 2012, 06:58 AM
    ebaines
    It would work on a hybrid car - as the gasoline engine drives the car forward the windmill could help charge the batteries. But it would be less efficient than simply charging the batteries using the engine-driven alternator or braking energy like they do today. The windmill idea would not work at all on a purely electric vehicle - the energy consumed due to drag caused by the wind mill would be geater than the energy that gets put into the batteries (if this wasn't the case then you would have a perpetual motion machine, which is impossible).
  • Apr 20, 2012, 12:20 PM
    7up
    Quote:
    Originally Posted by ebaines View Post
    It would work on a hybrid car - as the gasoline engine drives the car forward the windmill could help charge the batteries. But it would be less efficient than simply charging the batteries using the engine-driven alternator or braking energy like they do today. The windmill idea would not work at all on a purely electric vehicle - the energy consumed due to drag caused by the wind mill would be geater than the energy that gets put into the batteries (if this wasn't the case then you would have a perpetual motion machine, which is impossible).
    Could it work if u were changing from a small block v8 engine to a forklift generator?
  • Apr 21, 2012, 03:00 PM
    ebaines
    Not sure what you're getting at. No one said anything about a V8 engine - you're original question was about an electric vehicle. Please clarify your question.
  • Apr 22, 2012, 02:07 AM
    sinnadurai
    Quote:
    Originally Posted by ebaines View Post
    It would work on a hybrid car - as the gasoline engine drives the car forward the windmill could help charge the batteries. But it would be less efficient than simply charging the batteries using the engine-driven alternator or braking energy like they do today. The windmill idea would not work at all on a purely electric vehicle - the energy consumed due to drag caused by the wind mill would be geater than the energy that gets put into the batteries (if this wasn't the case then you would have a perpetual motion machine, which is impossible).
    Can you prove it by some calculations? Charging of batteries is done by freely available windpower and vehicle moves against some windload and friction between tyres and the road. If a)windmill is designed/constructed to be very efficient and b) EV designed to face less wind load and c)tyres/road are made to offer less friction ,it should work
  • Apr 23, 2012, 06:10 AM
    ebaines
    It can only work if the source of the wind is natural -if the wind speed > 0. Then sure - the windmill can get energy from the wind and convert it to electricity. But as I read the OP's post I assumed that he is asking whether the movement of air caused by the motion of the car could be used to power the car. And that's what can't possibly work. The calculations to show this are very straight-forward:

    Assume as the car moves at velocity v the force of the wind on the windmill is F. Since power is equal to force times velocity, the power available that the windmill may be able to turn into electricity is Fv. Note that v equals both the speed of the car across the road and the speed of the air relative to the car. This power is converted to electrical energy by the windmill and generator, but suffers some amount of loss since no mechanism is 100% efficient. Some of the loss factors include turbulence in the air flow across the wind mill blades, friction in the gearing of the windmill and generator, inefficiencies within the generator in converting mechanical energy to electrical energy, resistance in the wiring, inefficiencies in the storage and recovery of electricity in the car batteries, ineffciencies in the conversion of electrical energy to mechanical in the car's electric motor, friction in the car's transmission, and friction of the car's tires against the road. The power available to move the car is therefore eFV, where e = the overall efficiency of the windmill and power train, and e is less than 1.

    The power required to move the windmill against the air resistance F at speed v is FV. So the car requires a source of power equal rto FV in order for the windmill to generate power eFV. Since e<1, the power required to move the windmill against the wind is more than the power that is generated by the windmill. Therefore if you tried this on an electric car you would find that the car batteries are drained faster than if there was no windmill mounted on the car.

    This can all be summed up by saying that you cannot construct a perpetual motion machine.
  • Apr 24, 2012, 07:36 AM
    sinnadurai
    Quote:
    Originally Posted by ebaines View Post
    It can only work if the source of the wind is natural -if the wind speed > 0. Then sure - the windmill can get energy from the wind and convert it to electricity. But as I read the OP's post I assumed that he is asking whether the movement of air caused by the motion of the car could be used to power the car. And that's what can't possibly work. The calculations to show this are very straight-forward:

    Assume as the car moves at velocity v the force of the wind on the windmill is F. Since power is equal to force times velocity, the power available that the windmill may be able to turn into electricity is Fv. Note that v equals both the speed of the car across the road and the speed of the air relative to the car. This power is converted to electrical energy by the windmill and generator, but suffers some amount of loss since no mechanism is 100% efficient. Some of the loss factors include turbulence in the air flow across the wind mill blades, friction in the gearing of the windmill and generator, inefficiencies within the generator in converting mechanical energy to electrical energy, resistance in the wiring, inefficiencies in the storage and recovery of electricity in the car batteries, ineffciencies in the conversion of electrical energy to mechanical in the car's electric motor, friction in the car's transmission, and friction of the car's tires against the road. The power available to move the car is therefore eFV, where e = the overall efficiency of the windmill and power train, and e is less than 1.

    The power required to move the windmill against the air resistance F at speed v is FV. So the car requires a source of power equal rto FV in order for the windmill to generate power eFV. Since e<1, the power required to move the windmill against the wind is more than the power that is generated by the windmill. Therefore if you tried this on an electric car you would find that the car batteries are drained faster than if there was no windmill mounted on the car.

    This can all be summed up by saying that you cannot construct a perpetual motion machine.
    Power required=FV+Wind Force resisting motion of car x V+ Friction x V
    Power available=Baterry power+ eFV

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