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Topic Title: Electric Cars
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Created On: 25 July 2012 10:22 AM
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 25 July 2012 10:22 AM
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malcan2004

Posts: 3
Joined: 25 July 2012

Can someone telll why electric cars when moving can generate power when moving so that it keeps the main batteries charged. I know some have this on the wheels and charge when braking.
I just think if the car is moving there must be a way of powering a generator to keep the car charged so that you have continuous power and no need to charge the car at home or at a garage!
 25 July 2012 01:23 PM
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amillar

Posts: 1918
Joined: 28 May 2002

I think you may need to look up "perpetual motion" on Wikipedia! Yes, you can top up batteries during braking or on downhill runs, but you will not capture anywhere near enough energy to accelerate or get it back up the hill.

-------------------------
Andy Millar CEng MIET CMgr MCMI

http://www.linkedin.com/in/millarandy

"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert
 25 July 2012 02:49 PM
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ectophile

Posts: 529
Joined: 17 September 2001

Turning a generator isn't free; it takes mechanical energy.

In the case of regenerative braking, the generator is taking kinetic energy from the car and producing electricity. Removing kinetic energy slows the car down - which is what you wanted, and produces electricity to charge the battery - which is a handy side-effect.

Leaving the generator running all the time would produce a constant drag on the car (as if you were applying the brakes), and so you would have to send more power to the motors to make up for it.

The trouble is that the motors aren't 100% efficient, and neither is the generator. So the extra electricity you have to send to the motors is more than the generator is producing. The end result is a flat battery.

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S P Barker BSc PhD MIET
 25 July 2012 03:55 PM
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malcan2004

Posts: 3
Joined: 25 July 2012

Thanks for the replies I see what you are saying maybe we need the 40:1 ratio gearbox that was presented on Dragons Den to help drive the generator!
 12 August 2012 10:34 AM
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jackhowe

Posts: 1
Joined: 18 July 2012

Trucks have been using this technology for years but it only works when you are not accelerating. It's called a retarder in that application.
 12 August 2012 12:44 PM
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malcan2004

Posts: 3
Joined: 25 July 2012

Thanks Jackhowe I will have to look that up I have never heard of retarder before.
 20 August 2012 07:10 AM
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electricaltestinguk1

Posts: 11
Joined: 12 July 2012

Originally posted by: jackhowe

Trucks have been using this technology for years but it only works when you are not accelerating. It's called a retarder in that application.


I guess you're right. Because it will be no longer useful in some area that need speed.
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