In my late teens, a mate of mine was convinced that, but putting a propeller on the roof of an electric car, it would generate enough power whilst moving, to power the car.
Nobody could dissuade him from this belief, long conversations in the pub wouldn't convince him otherwise.
But, it got me thinking. With modern advances in turbines, batteries, aerodynamics etc - would you get enough energy back to make any difference?
Regenerative braking seems to work?
Put an aerofoil on the roof and you could sail it. There might be headroom problems though and you would need some other motive power to head closer than about 15 degrees into the wind. Tacking up the High Street is unlikely to be practical.
No more than 80% efficient at best though.
Colin Bignell
The propeller would create drag, no matter how efficient. This drag would be countered by more power having to be provided by the engine. Yes, sure, you'd get some of it back, but not nearly as much as the extra power from the engine needed to drive it.
You can't win, there are always losses (friction, turbulence, electrical resistance etc) they all end up as low grade heat.
On Wednesday 10 July 2013 21:21 The Medway Handyman wrote in uk.d-i-y:
Hi Dave,
Regen braking makes use of the fact you are trying to slow down, so you are converting kinetic energy no longer wanted into stored energy instead of heat in your brake discs.
Doing any sort of energy reclaim whilst you do not want to slow down (propeller on the roof) will just lead to net loss of energy as each component is inefficient.
Apart from things like electic cars, several classes of train do emply regen braking.
AFAIK, first used on trams to reduce brake wear.
Early trams and trains used it, but instead of feeding the power back into the system, they wasted it via a large resistor pack. In early trials, it had been known to blow various items in the supply system.
The large bolts I was making are for a regenerative braking system for a tr am. When the control lever is moved back to the braking area, the tram motors g enerate power that is applied to large solenoids that clamp directly on the rails, and also apply brake shoes to the wheels. The tram may also have ai r brakes and a manual handbrake. Other trams can feed power back into the overhead wires when slowing down, and all of them have large resistor banks for use at slow speeds, when most of the power is just wasted.
No. there are better ways to do it.
a little
There is one trick that works. with a propellor driven by the wheels, its is possible to travel straight INTO the wind, and also faster than the wind, downwind.
The energy balance works in that case.
But in still air the extra drag outweighs any stored energy
I encountered a pirate radio enthusiast who had his transmitter and aerial at a location where there was no mains. This was remote from the studio of course. He ran the tx from a huge 12V battery. The battery powered an inverter which powered the tx. Also powered by the inverter was a small battery charger, the output of which was connected to the battery. When we discussed this, the arrangement was new, and he told me, "Battery's gonna last for ever, innit! 'Coz I done put a charger on it! Clever innit?"
Bill
We have an electric wheelchair that uses it and it extends the range significantly.
Bill
All modern elecric cars have it. There is a dial on the instrument panel that works like a centre-zero ammeter (actually isn't) so you can see power going in and out of the battery. Power goes in descending hills and when slowing down. With practice, you never have to touch the brakes execpt when actually stopping.
Sure, you recover a good fraction of energy that would otherwise be wasted, but if there's one thing that electric cars are *not* it's perpetual motion machines ... most would struggle to move for 2 hours out of 12 without the aid of a fancy 50kW charger.
Which 50Kw charger is that? I charge mine from a 13a socket. It draws 10a
1Kwh takes me about five miles. So if I drive ten miles I have to charge it for an hour. I charge it off the PV panels, so "free petrol" when the sun is shining.Fast DC chargers exist, it takes twenty minutes from depletion.
I think from watching the instruments if you drive up a hill & back down, you get about half the energy back. Most energy loss is air drag. which of course you can't get back.
I didn't say they only work with rapid chargers, but the general pattern seems to be 12 hour for full charge from 13A socket, or around half an hour on a rapid charger.
With access only to conveniently placed 13A supplies, how many hours out of 12 could you spend in motion?
Is that specific to your model of car, the Leaf ones seem to be 80% charge in 25 minutes.
I have a Misubishi I-Miev
It takes eight hours from depletion to fully charge (could be overnight) from 13a socket There are also four hour AC chargers and the 20 minute DC ones Range is around 80 miles. Fine for most journeys. No road tax. In Summer, almost no fuel costs. About 1/8 fuel costs in Winter.
Locally made Leaf is coming out about now. Better range and cheaper. Allegedly. Leaf will take longer to charge, bigger battery/car.
Charge points appearing lots of places. Card operated mostly. Card costs
20/year. Some free in supermarkets. (For how long?) Not many DC ones. I don't have a card, don't need.
My modern diesel car has it, too. The energy saved is used to power 'things' when the engine stops at traffic lights, etc.
It does make a difference to the rate at which the car slows down.
On 11/07/2013 08:25, harryagain wrote: ...
Four in almost every local authority car park around here. I have never seen an electric car in one though.
Colin Bignell
Umm.. I'm not clever enough to argue this but the thread on the American
*up wind* propeller driven trolley ignored detail on the experimental methods used.AFAIR they used a rolling road and fan sourced wind. At the time I thought that the normal frictional losses from the various rotating parts were being met by unmeasured energy from the rolling road.
I could easily be wrong:-)
If the energy back was greater than the friction and the inefficiency of charging the battery, ie waste heat or whatever then it might save some money, but I'd imagine the reason why only braking is used is that this is the only way that is worth the extra cost. If you think about it any propeller thing adds drag as well as all the friction and above inefficiencies. Probably get more out of better aerodynamics. Brian
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.