# Kinetic Energy & EV's



## deanbo (Jun 7, 2010)

Is regenerative braking the only way to utilize kinetic energy on an EV?


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## tomofreno (Mar 3, 2009)

No. You can coast.


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## major (Apr 4, 2008)

deanbo said:


> Is regenerative braking the only way to utilize kinetic energy on an EV?


Besides coasting like Tom said.

Hmmm. Let's see. Utilize kinetic energy. That would be to change kinetic energy into another form of energy, I guess. 

Well, KE=½MV². So I guess you have to change the mass or the velocity of the EV. Utilize means to do something useful with the energy you get after converting it from kinetic energy. 

I can't think of anything useful from changing the mass of the EV, so that leaves changing the velocity. And since you don't want to charge the batteries from slowing down the vehicle which would be regenerative braking, what else is there? Maybe converting the KE into heat. That would be dynamic braking. And I guess you could find something useful to do with the heat, like warm the cabin on a cold day.

Other than that, I'm hard pressed to come up with anything useful, unless you think smashing into something would be of use 

Beats me,

major


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## Duxuk (Jul 11, 2009)

One thing you could do with kinetic energy is to convert it to potential energy. This involves getting some speed up then going up a hill. With the throttle closed and the benefit of no friction you will convert 1/2mv^2 into mass*height * acceleration due to gravity. It's a bit sad that climbing hills take quite a lot of energy. Rearranging the equation shows that the height climbed will be 1/2v^2/G so 44mph will see you grind to a halt after a little over 20 meters of climbing. Still you will later be able to turn around and get back to where you started with no expenditure of energy and arrive at 44mph in a world of no friction or wind resistance.

Come to think of it, slowing on a climb will avoid heating the motor due to high ampage draw-a real saving of energy!


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## Wirecutter (Jul 26, 2007)

major said:


> Other than that, I'm hard pressed to come up with anything useful, unless you think smashing into something would be of use
> 
> 
> 
> major


Exactly what I was going to suggest. It might be useful one time, for entertainment value. 

-M


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## major (Apr 4, 2008)

deanbo said:


> Is regenerative braking the only way to utilize kinetic energy on an EV?


 


major said:


> Other than that, I'm hard pressed to come up with anything useful, unless you think smashing into something would be of use


 


Wirecutter said:


> Exactly what I was going to suggest. It might be useful one time, for entertainment value.


 
Demolition derby


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## IamIan (Mar 29, 2009)

major said:


> I can't think of anything useful from changing the mass of the EV,


E=MC^2



ok ... so we can't do like Star Trek does and convert the mass to energy ... but boy would that be a nice ... Carry around a lead bar as fuel  hahaha

The closest we've come is H + H = He ... Fusion ... and that is a very very long way off from vehicle ready.

- - - - - - - - 

In a practical sense ... the Kinetic energy can be used one way or another for anything you would use energy for ... but because you can't reach 100% efficiency you're usually better off conserving it as Kinetic energy when you have it than trying to convert it... unless you want to lose mass or velocity for some other reason... but that pretty much gets you back to regenerative braking.


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## Woodsmith (Jun 5, 2008)

Something that F1 cars have been playing with is KERS, Kinetic Energy Recovery System, using flywheels to store breaking energy and then using that stored energy to boost acceleration.


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## major (Apr 4, 2008)

Woodsmith said:


> Something that F1 cars have been playing with is KERS, Kinetic Energy Recovery System, using flywheels to store breaking energy and then using that stored energy to boost acceleration.


Hi Wood,

I am a Formula One fan. Attended several US Grand Prix races at Indy. Watch most races live on TV (at all hours of the day here in the US of A). Pretty exciting stuff. Speed, competition and technology. So I was really keen on KERS last year. Had watched KERS development from magazines (like SAE) the year prior. I expected more than I got last year. And then they dropped it this year.

KERS was supposed to be regenerative braking to charge an energy storage system (ESS). And then to use that stored energy for a 60 kW boost at the driver's discretion. IIRC, this was limited to 10 seconds of boost per lap.

To my knowledge, three types of systems were developed (or at least considered), electrical, hydraulic and mechanical (flywheel). It was optional last season and only 2 teams deployed and raced with KERS. Both were electrical using battery storage, I think. F1 plays the technology pretty tightly, so I may not have all the facts straight.

Last season during the races, the coverage on TV would often show an icon for the car in the form of a battery symbol displaying the state of charge (colored fill). Of course, I, having done quite a lot of work with regenerative braking, was particularly interested in when the battery would be charged during the lap. I was greatly disappointed to see the icon fully recharged each time the car crossed the start/finish line. On almost all venues, this happens under straight line hard acceleration, not braking. The icon would empty as the driver used his boost allotment when he used it, but would always refill at the start/finish line.

So, was this just the media's feeble attempt to simplify KERS for the viewer? Or was it in fact a boost system which sucked the recharge energy off the engine instead of braking? These F1 cars have friction brakes which can exceed several megawatts of power under hard deceleration events. So a 60 kW regen system isn't going to do much in terms of assisting the decel. However, because engine power is closely matched between teams, a 60 kW boost is quite noticeable.

I have been busy this season, but have seen all but one of the F1 races so far. Several on tape, well DVR. So I miss all the scuttlebutt. I don't know if they intend to bring back KERS or not. If so, I hope they do a better job of relating its use to the viewer.

Point is, regardless of whether KERS is electric, hydraulic or mechanical, it is, or supposed to be, regenerative braking and boost assist with the recovered kinetic energy. All three types of regen systems have been developed and tried on passenger cars and commercial vehicles. And they all work. Flywheels are uncommon. Hydraulic is being used on some UPS delivery vans and refuge collection trucks. Electrical is the most common, on battery (BEV) and hybrids (HEV).

Now this is a DIYelectriccar forum. And the battery electric system is reversible, meaning the vehicle motion can result from energy taken from the ESS or energy can be put into the ESS from the vehicle motion. [Yeah, I know you guys with series motors.....] So the BEV benefits little from the addition of a second ESS such as flywheel (which is kinetic or inertia) or hydraulic (which is really compressed gas). 

These non electric regen systems can in fact be of value on vehicles using non reversible ESS like gasoline engines. This makes them flywheel hybrids or hydraulic hybrids. Kind of off-topic on an electric car forum if you ask me 

Just my gripe about F1 KERS,

major


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## Duncan (Dec 8, 2008)

Hi Major

I was extremely disappointed that the teams agreed not to use KERS this year,
I believe that it did use energy from braking but that the apparent re-charge at the start/finish line was to do with the rules limiting it to 10 seconds/lap
So that no matter how much you had in the "battery" you could only use 10 seconds and you could use another 10 seconds as soon as you were across the line

Over the years I have been disappointed by the rule makers in F1
Just after they banned turbos I read a superb Honda article about "The engine in the glove box"
The Honda chief engineer was looking forwards to having a 100cc engine in a saloon car
small enough to tuck it away somewhere
F1 development was driving that until they pulled the plug!

The next miss was active suspension and driver aids - Nigel Mansel's Williams was apparently so easy to drive anybody could drive it
(the rumor was that Nigel only became competitive when the intercoms became good enough that his engineer could shout "middle pedal Now")
Then they banned it!!

What do you think of Audi's project for an un-manned attempt on Pikes Peak?


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## TomA (Mar 26, 2009)

From a F1 perspective, KERS was an expensive gimmick that (usually) benefited the two (top) teams that could afford it, magnifying existing inequalities on the track, driving up expenses, and proving almost nothing technically. Great technology, but it wasn't good for _racing_. 

F1 isn't just a developmental playground for automotive and aerospace technology. It is a racing series in which parity and competitive opportunities are very difficult to maintain. If the gear doesn't improve the _racing_, then it isn't worth it. I remember Ayrton Senna's driver aids being so sophisticated that he could "record" the throttle and brake inputs on a really hot lap, then press "play" the next time around at the start/finish line, leaving him only to steer the car thereafter. How is that good for racing?

Same thing with KERS. In practice, it just makes the already fastest cars impossible to pass, or impossible to hold off if they want to pass. That's a dead-end for the sport, regardless the technology.

TomA


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## Duxuk (Jul 11, 2009)

I remeber seeing Lewis Hamilton making several excellent passing manouvres using KERS. He was held back last year by other deficiencies in the car, particularly the aerodynamics. I think that if KERS were NOT restricted to just 10 seconds per lap, then any car NOT fitted with the system would stand no chance. 

This may be an area where supercapacitors rather than batteries could be useful. They could charge almost instantly and discharge equally rapidly, if required. 

Not sure I'd fancy a DIY EV with a built in thundebolt attatched, though!

Andrew.


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## Duncan (Dec 8, 2008)

Hi TomA

Disagree/Agree
The technical race is important or it would all be Formula Ford (or NASCAR)

The best way to bring back the racing would be

No wings
Bodies to have an oval cross section
Minimum weight

Engines - free - BUT have to do race on 250 liters fuel supplied by organizers who will buy from cheapest supplier within 50km of track

Cut out all this aero nonsense, braking distances increase, cornering speeds go down
can get the spectators closer again


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## major (Apr 4, 2008)

Duncan said:


> Disagree/Agree
> The technical race is important


Hey,

I agree/disagree. 

But let's keep the thread on track. Kinetic energy.

And EVs.

And for that I see F1 KERS as a positive.

Although the OP may be long gone by now, I enjoy the discussion.

major


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## TomA (Mar 26, 2009)

I think on balance KERS was good, but it is more of the same "hybrid" stuff that really doesn't move the EV ball very much. And public awareness of F1 in the US is basically nil, let alone awareness of KERS. 

Nowhere else in the world could I miss a race, and comfortably wait as long as I like to see it on TIVO, confident that I will _never_, even by looking at a sports page or watching sports on the TV news, be accidentally made aware of the results. Quite amazing, really.

Far more useful for EV development will be growing the population of racing machines in the electric classes that already or shortly will exist- first at dragstrips, hillclimbs and LSR courses, then maybe at road courses. I don't see much application for roundy-round racing, either on superspeedways or shorter ovals, but one never knows. If we could get just a little of the money that already goes into ICE racing into _EV_ racing, everything from controllers to motors and even instrumentation would get a whole lot better in very little time. 

TomA


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## major (Apr 4, 2008)

TomA said:


> I think on balance KERS was good, but it is more of the same "hybrid" stuff that really doesn't move the EV ball very much. And public awareness of F1 in the US is basically nil, let alone awareness of KERS.
> 
> Nowhere else in the world could I miss a race, and comfortably wait as long as I like to see it on TIVO, confident that I will _never_, even by looking at a sports page or watching sports on the TV news, be accidentally made aware of the results. Quite amazing, really.
> 
> ...


Nicely said TomA,

Thanks,

major


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## RoughRider (Aug 14, 2008)

Porsche made a racecar for this years 24h-race with a flywheel...position 4 in the picture...

NO batteries inside the car...

the car was leadng the race...couple of hours before the end of the race, tha gasoline motor gave up...

the electrical system and the flywheel were stil doing great


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## Duxuk (Jul 11, 2009)

Sorry if I'm straying from the point but have you seen the results of the Isle of Man electric race TT Zero?
The Moto Cyz....(however it's spelled!) lapped at just shy of 100mph, a mark that was first beaten in, from memory, 1957 after 46 years of competition and developement on the mountain circuit. Where will the EV motorcycles be in even another 10 years?

There is a good website with the results if you Google IOM TT.


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## major (Apr 4, 2008)

Duxuk said:


> Sorry if I'm straying from the point but have you seen the results of the Isle of Man electric race TT Zero?
> The Moto Cyz....(however it's spelled!) lapped at just shy of 100mph, a mark that was first beaten in, from memory, 1957 after 46 years of competition and developement on the mountain circuit. Where will the EV motorcycles be in even another 10 years?
> 
> There is a good website with the results if you Google IOM TT.


Hi Dux,

http://www.diyelectriccar.com/forums/showthread.php/tt-zero-isle-man-motoczysz-wins-45949.html 

Also http://www.diyelectriccar.com/forums/showthread.php/ttxgp-race-road-america-45853.html 

And http://www.diyelectriccar.com/forums/showthread.php/ttxgp-race-infineon-45085.html 

Them 2 wheelers are gettin' up there 

major


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## deanbo (Jun 7, 2010)

Just to throw something else at you "old timers", would you say kinetic energy can exceed potential energy (battery power) for a period of time in a car? Say if heading downhill? Is it worth placing a tax on this kinetic energy via way of some sort of in hub re generator because of this?

I look at like this. If kinetic energy exceeds potential energy over the entire distance of the trip, then you will have achieved over unity (perpetual energy?) which is not possible in my opinion. But at times during the trip, kinetic energy will exceed potential energy. Downhill for example. 

Is it worth placing a regenerative tax on this kinetic energy if you are heading downhill? Or should I say if the regenerative device adds another 10 kgs to a one tonne vehicle, is it going to place a signifcant tax on the kinetic energy heading downhill?

Would the energy gained via this regnerative device be enough to charge the batteries so they will take you further up the other side (not to the top) once the 1% tax via way of extra weight on the vehicle is taken into account not only on the kinetic energy that was just created but the extra potential energy (1% increase in weight) now needed to power the vehicle up hill as well.

To sum up my argument, when you create potential energy with an EV you are also creating kinetic energy. To my mind the only time you are not creating kinetic energy as well as potential energy when you are driving is when you are stopped. But at the risk of repeating myself kinetic energy can never exceed potential energy for the duration of the trip. But is this kinetic energy really being utilized properly with regen?


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## major (Apr 4, 2008)

deanbo said:


> Just to throw something else at you "old timers", would you say kinetic energy can exceed potential energy (battery power) for a period of time in a car?


Us old timers might think that potential energy is the energy of a particle or system of particles derived from position, or condition, rather than motion. A raised weight, coiled spring, or charged battery has potential energy.* Whereas kinetic energy is derived from motion. 

And us old timers might know the difference between energy and power.



> when you create potential energy with an EV you are also creating kinetic energy


And us old timers might know you cannot create energy. God can. But all us old timers can do is convert energy from one form to another.

*from answers.com


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## Guest (Jun 13, 2010)

So with your foot off the break have another car hit you from behind at about 30 mph. If car number two is paying for their own gas you are traveling for free.


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## Jan (Oct 5, 2009)

notmrwizard said:


> So with your foot off the break have another car hit you from behind at about 30 mph. If car number two is paying for their own gas you are traveling for free.


Great idea. I need to redesign the back of my car. A bit.


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## TomA (Mar 26, 2009)

notmrwizard said:


> So with your foot off the break have another car hit you from behind at about 30 mph. If car number two is paying for their own gas you are traveling for free.


All joking aside, tapping the wake energy of other vehicles in motion is quite worthwhile.

Its the principle underlying NASCAR "freight train" superspeedway drafting practices; the reason porpoises often ride the pressure wave at the bows of ships, why geese fly in a delta formation; how bicycles are able to go 150mph tucked into the wake of cars running just ahead of them; and, in an apparently circular and weird way, how the near-mythical Aurora wave-rider plane (that the USAF insists has never existed) is supposed to work- it is able to cruise at high speed by surfing on the bow shock of its own hypersonic wave. Trippy...

Regardless, there is a lot of kinetic energy to be tapped in the wake of anything moving through a fluid, either water or air.

TomA


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## IamIan (Mar 29, 2009)

TomA said:


> All joking aside, tapping the wake energy of other vehicles in motion is quite worthwhile.
> 
> Its the principle underlying NASCAR "freight train" superspeedway drafting practices; the reason porpoises often ride the pressure wave at the bows of ships, why geese fly in a delta formation; how bicycles are able to go 150mph tucked into the wake of cars running just ahead of them; and, in an apparently circular and weird way, how the near-mythical Aurora wave-rider plane (that the USAF insists has never existed) is supposed to work- it is able to cruise at high speed by surfing on the bow shock of its own hypersonic wave. Trippy...
> 
> ...


All the energy you refer to was already put out by the lead object ... the truck you are drafting ... the pace car everyone else is drafting ... the lead goose ... etc...

You are just transferring some of the energy spent by the lead vehicle to the drafting / tailing vehicles.

Additionally you don't even get all of it ... some is converted to sound , heat, wind pressure going in different directions than your direction of travel.... etc.

Therefore you would actually be able to go further and do better with the same energy without wasting it on bad aerodynamics , or bad fluid-dynamics on the lead object.


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## Duncan (Dec 8, 2008)

Deanbo

Lets have one more go at this

You start off stationary - the car has potential energy in its batteries call this 100

you accelerate, some of your 100 goes to become kinetic energy you now have 95 in the battery 5 in kinetic

as you drive you have to keep topping up the kinetic after five minutes you have 90 in the battery and 5 kinetic

THE TOTAL ENERGY KEEPS GOING DOWN

If you are using potential energy from the batteries to accelerate the car the Kinetic energy you gain is always always always LESS THAN the potential energy you lose

Back to the swimming pool analogy

You have a pool with a leak - (energy to keep travelling)
You are taking water from your pool - throwing some away and putting the remainder back in the pool

If you just let it leak it will last longer than if you continue taking water from your pool - throwing some away and putting the remainder back in the pool

You cannot Win
You cannot break even
You cannot leave the game

IanIan

You can win in this case - like riding in a Peleton, the lead rider works as hard as if he was on his own, the other get an easy ride and you keep swapping leaders
The combined pack of 20+ bikes has better aerodynamics than 20 individual bikes

In the NASCAR example the leader gets a "push" from having effectively a longer vehicle and a reduction in form drag


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## deanbo (Jun 7, 2010)

Firstly imagine a car accelerated to 10 kph and then crashed into a brick wall. Secondly imagine a car accelerated to 20 kph and then crashed into a brick wall with all other variables constant to the first car. 

Does it take twice as much battery power to accelerate the vehicle to 20 kph or did it take more than twice the amount of battery power all other variables remaining constant.

When the second car hits does it do twice as much damage to the vehicle? More than twice as far as I am aware so where was the energy to do more than twice the amount of damage coming from?

If the amount of damage in the second car was proportional to the increase in the amount of battery power consumed then I believe you could say it was just the energy from the batteries. Otherwise?


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## major (Apr 4, 2008)

deanbo said:


> Firstly imagine a car accelerated to 10 kph and then crashed into a brick wall. Secondly imagine a car accelerated to 20 kph and then crashed into a brick wall with all other variables constant to the first car.
> 
> Does this do twice as much damage to the vehicle? More than twice as far as I am aware so where was the energy to do twice the amount of damage converted from?
> 
> Lastly did it take twice as much battery power to accelerate the vehicle to 20 kph or did it take more than twice the amount of battery power all other variables remaining constant. I don't know the answer to this question which is why I ask.


I refer to this:


GerhardRP said:


> Go find your junior high school science book. Read up on this guy named Newton. When you understand his laws, you can answer this question.
> Gerhard


And:


major said:


> KE=½MV²


Do you read anything we write?


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## deanbo (Jun 7, 2010)

Thanks for that.

By my calculations (hope I've done it correctly) the first car is KE = ((0.5 * 1000 kgs) * (10kph x 10kph)) or 50,000. 

Second car would be 200,000. So is something rising at the square of speed? Also does this mean it takes four times the amount of power from the batteries to increase the car from 10kph to 20kph?


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## major (Apr 4, 2008)

deanbo said:


> Thanks for that.
> 
> By my calculations (hope I've done it correctly) the first car is KE = ((0.5 * 1000 kgs) * (10kph x 10kph)) or 50,000.
> 
> Second car would be 200,000. So is something rising at the square of speed? Also does this mean it takes four times the amount of power from the batteries to increase the car from 10kph to 20kph?





major said:


> And us old timers might know the difference between energy and power.





GerhardRP said:


> Go find your junior high school science book. Read up on this guy named Newton. When you understand his laws, you can answer this question.
> Gerhard





major said:


> But all us old timers can do is convert energy from one form to another.


Seriously, you need to study a bit of basic physics.


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## deanbo (Jun 7, 2010)

Old timers was in quotes for a reason. As for the rest, I didn't think asking electrical engineers on this forum about the math was too irrelevant.


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## major (Apr 4, 2008)

deanbo said:


> Old timers was in quotes for a reason.


And what was that reason?



> As for the rest, I didn't think asking electrical engineers on this forum about the math was too irrelevant.


Do you go to an accounting forum and ask questions without knowing basic arithmetic?

These are not electrical engineering questions. Just questions improperly worded about basic physics which indicate you lack the basic understanding of basic physics. I (and I presume other members) have no problem (in fact like to) help people out with questions about EVs. But I (and I presume other members) get disturbed when somebody goes on and on about something relating to basic concepts or basic science which can be easily researched in text books (which you should have studied in high school) or easily found on hundreds of web sites.

Sorry, I don't intend to be mean or disrespectful, but do your homework and come back with some intelligent questions.

Regards,

major


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## deanbo (Jun 7, 2010)

major said:


> And what was that reason?
> major


Sarcasm which I thought was fairly obvious due to the highlighting of the words "old timers". If you want to take offence to that then it's due to your own assumption which has nothing to do with me.


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## TigerNut (Dec 18, 2009)

deanbo said:


> Thanks for that.
> 
> By my calculations (hope I've done it correctly) the first car is KE = ((0.5 * 1000 kgs) * (10kph x 10kph)) or 50,000.
> 
> Second car would be 200,000. So is something rising at the square of speed? Also does this mean it takes four times the amount of power from the batteries to increase the car from 10kph to 20kph?


I worked this scenario in one of your earlier threads about a week ago...
You used the incorrect units. This matters because you won't get numerical values that make sense otherwise. You should convert the speed to meters per second (in SI units). Then if the mass is given in kilograms, the energy comes out in Joules. http://en.wikipedia.org/wiki/Joule

However, no matter what units you use, the fundamental relationship is the same, as your numbers illustrate. Doubling the speed gives you four times the energy stored in the moving object, which also means it requires four times as much *energy* from the batteries to get going that fast.

Note that I said energy, not power, as you wrote. The difference is crucial. Power is how much energy you can transfer in a certain amount of time; its units are watts, which is is equivalent to Joules per second.

The concepts of conservation of energy and Newton's laws, as everyone else is trying to tell you, are part of highschool physics courses, and may even be part of some junior highschool advanced science studies. Until you get that stuff worked out, leave your sarcasm at home, ok? You've started three or four threads on this forum, all asking questions about basic physics and your notions that you can somehow get more energy from a system than what you've put in. In every single thread, the response has been uniform: It doesn't work that way. That's not because we're all old farts with ossified brain cells. It's because it really doesn't work that way. You can put together some Rube Goldberg devices that make it hard to measure the energy gain or loss of different parts of the system, and thereby try to justify your theories, and many people have done so. But eventually these people are all exposed as scammers. When you break down the system to its bare essentials, or take sufficient and correct measurements of the energy flow in any given system, you will see that there is no energy gain that is not accounted for by an energy loss somewhere else in the system.


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## IamIan (Mar 29, 2009)

deanbo said:


> Also does this mean it takes four times the amount of power from the batteries to increase the car from 10kph to 20kph?


As others have said their is a difference between power and energy.

But it is even worse than 4x... you found there.

The aerodynamic losses against the vehicle are exponential
4x larger when the vehicle moves 2x as fast
9x larger when the vehicle moves 3x as fast
16x larger when the vehicle moves 4x as fast
25x larger when the vehicle moves 5x as fast.
etc...

In addition to Aerodynamic losses there is also rolling resistance losses that also increase with speed... at least those are more linear.

But those are just losses ... those are some of the forces that are constantly working against you ... they are constantly trying to slow you down ... if you do not keep pumping more energy into it... those sources of losses will bring any vehicle to a stop from any speed it travels at given enough time.

This is the part people have wrote about you can't break even... 

If you want 100 Wh of energy in Kinetic form.
At 80% efficiency 
you have to put in over 125 Wh of energy. 
If you are applying that energy at a rate of 25 Watts of power. 
It would take you 125 Wh / 25 W = 5 hours. 
To apply that 125 Wh of energy... to get 100 Wh of Energy in the form you wanted. 

Even though you have applied and used 125 Wh of energy , sense you are only 80% efficient you only converted 100Wh of it to the form you wanted. The other 25 Wh are converted to things you didn't want ... light , heat, radio static , etc...

clear as mud?


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## deanbo (Jun 7, 2010)

Getting clearer. For my idea to have worked the generator would need to have been independent from the motor and transmission? I'm bringing up this link as a new example because the generator isn't physically connected to the transmission in any way?

Would it however create magnetic drag and if it did would it now tie this device to the transmission because of it? Basically anyone have any idea if it would be feasible to take this same approach for use as a KERS on a car?


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## TigerNut (Dec 18, 2009)

deanbo said:


> Getting clearer. For my idea to have worked the generator would need to have been independent from the motor and transmission? I'm bringing up this link as a new example because the generator isn't physically connected to the transmission in any way?
> 
> Would it however create magnetic drag and if it did would it now tie this device to the transmission because of it? Basically anyone have any idea if it would be feasible to take this same approach for use as a KERS on a car?


The basic principle is that you don't get anything for free, no matter how the system is connected to your vehicle. This generator you linked to would indeed extract some energy from the moving vehicle. You should consider it to be connected to the transmission through the road.

The reason why cars don't have generators in their wheels is that doing so adds a great deal of mass to the unsprung portion of the vehicle, which affects the handling in a nasty way. Some race cars and high end street vehicles (Jaguars, for example) even move the rear brakes to the inboard end of the rear drivetrain so that the unsprung mass is minimized.

While the mass of the generator you linked to is obviously not much, a generator that is rated for the power levels you would need to create an effective energy recovery system would be very heavy and large - figure that it would be at least half the size of the electric motor.

This setup will still only recover a small fraction of the energy applied to get the vehicle going. Here's one thing you need to think about: Say your energy recovery system weighs 100 pounds in a 2000 pound car, and on deceleration it only recovers 5% of the energy used to accelerate the car (nevermind what you use to overcome aero drag and friction on a continuous basis). If you threw the recovery system overboard then you would have made the car 5% lighter, which would result in the same energy savings, without the cost and complexity of the energy recovery system.


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## IamIan (Mar 29, 2009)

deanbo said:


> Getting clearer. For my idea to have worked the generator would need to have been independent from the motor and transmission? I'm bringing up this link as a new example because the generator isn't physically connected to the transmission in any way?
> 
> Would it however create magnetic drag and if it did would it now tie this device to the transmission because of it? Basically anyone have any idea if it would be feasible to take this same approach for use as a KERS on a car?


If generator is 90% efficient ...

When it takes 100 Wh of kinetic energy away from the vehicle ... it slows the vehicle down by 100 Wh worth of kinetic energy ... but as 90% efficient it will only give you 90Wh of electrical energy ... the other 10Wh of energy is wasted to things you do not want ... heat, light, radio static, sound , etc...

Now where did the vehicle get that 100 Wh worth of kinetic energy in the first place?

If it is a EV and the drive motor is 90% efficient ... to get 100 Wh worth of kinetic energy out you have to put ~111 Wh worth of electrical energy into the drive motor.

So at best ... even if we ignore the % efficiency of the motor controller electronics ... and the cycle efficiency of the batteries to store the energy ... and we ignore losses from things like aerodynamics, rolling resistance , transmissions, etc...

in an ideal world ... you supply your ( 90% efficient ) drive motor with ~111 Wh worth of electricity to get 90Wh worth of electricity back from your 90% efficient generator.

so yes... it works ... but as others have said ... you can't even break even.

As far as I know KERS ( even though it was setup differently ) still suffered the same kind of energy waste / efficiency losses ... it was not a method of increased efficiency ... it was a method of short term power boosting.

- - - - - - - 

Now for the sake of simplicity I suggest avoiding the more complex interactions of how some power boosting systems can be used to increase the vehicles operating efficiency... that is a topic you can work up to ... the short answer is that there are trade offs and break even points ... bellow a break even point it is a operating loss... above a break even point it is a operating gain.

... but each step ... each conversion ... is always less than 100% efficient.

The energy always .... always .... always ... has to come from something ... from somewhere.... something else always has to give up energy for you to get it.


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## TomA (Mar 26, 2009)

IamIan said:


> As far as I know KERS ( even though it was setup differently ) still suffered the same kind of energy waste / efficiency losses ... it was not a method of increased efficiency ... it was a method of short term power boosting.



Correct, and the thing to remember about F1 is "efficiency" really isn't part of the game. The cars disturb the air so violently that the fences around the track wave in and out when just one car goes by. They brake so hard the carbon discs glow red, the tires and even the track surface are ruined from the friction. They generate (and shed) so much heat that if the airflow around the cooling or exhaust systems is even slightly disrupted,
there is often a fire. Formula One is an awesome example of the precisely directed discharge of extravagant amounts of energy, not its conservation...

TomA


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## deanbo (Jun 7, 2010)

IamIan said:


> If generator is 90% efficient ...
> 
> When it takes 100 Wh of kinetic energy away from the vehicle ... it slows the vehicle down by 100 Wh worth of kinetic energy ... but as 90% efficient it will only give you 90Wh of electrical energy ... the other 10Wh of energy is wasted to things you do not want ... heat, light, radio static, sound , etc...
> 
> ...


This particular idea for regenerating energy would only regenerate energy when the brakes are applied. The extra energy requirement from the batteries would be because of weight, nothing else as brakes do not require electrical energy in any way, shape or form to function.


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## IamIan (Mar 29, 2009)

deanbo said:


> This particular idea for regenerating energy would only regenerate energy when the brakes are applied. The extra energy requirement from the batteries would be because of weight, nothing else as brakes do not require electrical energy in any way, shape or form to function.


Upgrading conventional friction brakes to regenerative brakes can help with your net efficiency ... but , only if you can disconnect the generator when you are not braking.

The other thing to keep in mind ... is that even upgrading to regenerative braking will have a break even point.

Bellow the break even point the addition weight from batteries , controllers, etc... which any increase in weight reduces your vehicle efficiency of travel ... bellow a certain point the cost of that weight is a larger impact than the beneficial impact of the regenerative braking.

Above the break even point the regenerative braking improves your vehicle net efficiency more than the additional weight reduces it.

To get a better idea of where that break even point might be ... one of the first things I would recommend ... is to starting doing some pen / paper work of sizing things out a bit ... how much battery storage ... how big of a generator ... how is the generator going to be attached .... etc... when you get your initial rough draft idea put together than you can start to narrow down the break even point a bit better.

One more thing ... because we still are always less than 100% efficient ... when possible it is more efficient to watch and learn to better predict the traffic in front of you , and around you ... the more you can converse the kinetic energy / momentum you already have the better your vehicle efficiency will be... when you were not able to predict the traffic well enough ... and you have to apply brakes... it is then that regenerative braking can be a benefit.

The more highway type driving you do , generally speaking the less beneficial regenerative brakes are... highway driving is easier to predict the traffic in front of you and thus easier to do the more efficient option of conservation of the momentum / kinetic energy you already have.


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## deanbo (Jun 7, 2010)

IamIan said:


> Upgrading conventional friction brakes to regenerative brakes can help with your net efficiency ... but , only if you can disconnect the generator when you are not braking.
> 
> The other thing to keep in mind ... is that even upgrading to regenerative braking will have a break even point.
> 
> ...


Thanks IamIan. It sounds like you understand my theory very well. I didn't realise the generator would have to be disconnected when brakes are engaged. Is this because the extra weight could cause the motors shaft to break? As you say, if the motorist does not brake enough to outweigh the penalties this idea would impose, then this idea would run at a loss. 

I look at one aspect of this idea in terms of how much weight would a system like this add as a percentage to the current total weight of the vehicle, and as you say how much more penalty on the batteries will this weight impose?

Can super caps be used instead of batteries? If so are super caps lighter than batteries? What is the minimum amount of braking that is required to break even? For example do you only need to accelerate from 0 to 10 kph and then brake to a stop to break even? And so forth. 

What I think would be even better than this idea is if the motor could do all the required braking. Brakes front and rear would be eliminated saving weight in the process. Is this an impossible idea? In the meantime I'm following my idea. Wish me luck.


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## Duncan (Dec 8, 2008)

Hi Deanbo

You will still need brakes
I explain
My car is a Subaru - 4wd if I replaced the IC engine with a motor/generator then I could use the generator function to brake on all four wheels

How powerful (and heavy) a generator would I need to replace my brakes?

I need to be able to stop fast from high speed in an emergency

Vehicle mass - 1600Kg
Speed - 180 km/hr 
Deceleration - 0.75G

*These are not high numbers my brakes can easily exceed these*

Force required = 1600Kg x 0.75G x G(9.81 call it ten) = 12,000 N
Power needed = Force x distance/time = force x speed

180 Km/hr = 50 m/sec x 12,000N = 600 Kwatts = 800 Hp 

My fairly light weight brakes can apply over 800 hp worth of braking when required

Just think of how much an 800 Hp motor would weigh!

I don't need to do this very often (maybe once in five years) so there is not much available energy to harvest BUT I do NEED to be able to do it in an emergency


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## IamIan (Mar 29, 2009)

Duncan said:


> You will still need brakes


Agreed.

Regen is a nice add on ... or upgrade ... But I don't think it should be used as a replacement for conventional brakes.



deanbo said:


> I didn't realise the generator would have to be disconnected when brakes are engaged. Is this because the extra weight could cause the motors shaft to break?


There are several reasons ... breaking a shaft ... would not have been one of mine ... and I would put it low on the list... any regenerative system worth having will not threaten the safety of the vehicle by breaking shafts and such.

A short list of a few reasons to have the regenerative braking generator disconnect.

#1> same reason you don't drive around constantly applying normal brakes... when you are trying to accelerate a generator that is trying to slow you down is counter productive ... when you are trying to maintain a steady speed a generator that is trying to slow you down is counterproductive... when you are going up a hill having a generator trying to slow you down is counter productive.

#2> Your batteries have a finite limited ability to store the energy the generator sends to them ... once they reach 100% SoC ... if you keep pumping more into them you will kill the batteries... and possibly cause a fire.

If you shunted the generators converted energy from slowing your vehicle down to something that didn't store the energy ... like and old school regenerative braking from trains ... a large heating element for instance... now you are just throwing away the energy , and are no better than just using conventional friction brakes... might as well save the extra weight.



deanbo said:


> As you say, if the motorist does not brake enough to outweigh the penalties this idea would impose, then this idea would run at a loss.


Correct.

Further ... conversing momentum by staying alert and better predicting the traffic ahead of you ... is not only safer driving ... but is also more efficient ... when you have to brake regenerative brakes that can store some of the energy can be better than conventional friction brakes.



deanbo said:


> I look at one aspect of this idea in terms of how much weight would a system like this add as a percentage to the current total weight of the vehicle, and as you say how much more penalty on the batteries will this weight impose?


Depends on how much you want.

The more braking power you want the larger the motor and the controller and the batteries to power them.

Also depends on how it is implemented not all designs are equal.



deanbo said:


> Can super caps be used instead of batteries? If so are super caps lighter than batteries?


Capacitors even Super Caps ... are great for high power pulses for short periods of time ... so in that sense they can take and give more ( kw ) than batteries of the same weight ... but capacitors have low energy density ... which means they can not hold as much energy ( kwh ) for the same weight ... so they will empty out faster and fill up faster ... and just over all hold less energy.

Not all Batteries are created equal either ... some can take reasonably high charge and discharge rates ( kw ) ... others can not... and some hold more energy ( kwh ) per unit weight than others.

In general there is no one option that is best at everything ... it ends up being a balancing act among the choices where you have to give up a bit of one thing to get a bit more of something else ... and you find a balance for your specific design needs and the budget you have to work with.



deanbo said:


> What is the minimum amount of braking that is required to break even?
> For example do you only need to accelerate from 0 to 10 kph and then brake to a stop to break even? And so forth.


It is still most efficient and best to be able to better predict the traffic and need to brake less ... conserve the momentum / kinetic energy you already have ... remember no conversion is 100% efficient ... so converting it to anything will loose some along the way.

To figure out where a break even point is ... you need more than just a change in speed ... how much mass is changing that much in speed? ... how fast is it changing that much in speed ( what is the rate of change ) ? ... how much weight did the regenerative braking system add? ... what do the efficiency curves look like for the motor / controller / batteries? What is the rating of your regenerative braking system? ( how much of this kinetic energy & electrical energy can it handle? )

As an example:
In general rolling resistance is linear with vehicle weight.
If you increase your vehicle weight by 10% ... you will also increase your rolling resistance at all times by 10%... so if you normally use ~100 wh of energy ( just on rolling resistance ) over a given course/distance and then you add 10% to your vehicle weight ... you can expect the weight increase to now cause you to need at least ~110 Wh of energy ( just in rolling resistance ) to travel the same course / distance... if all other variables ( wind , humidity , temperature, etc. ) are all the same... a regenerative braking system when used that recovered more Wh over that trip than the increase in weight cost you ... might break even... or might be a benefit.

But if I can travel the same route and improve my driving skills and ability to better predict traffic I am not only safer ... but it is more efficient... even more efficient than regenerative braking can be ... at least for as often as you can do so ... sometimes you will need to brake, no matter how good you are... and it is in those times that regenerative braking can be a benefit.



deanbo said:


> What I think would be even better than this idea is if the motor could do all the required braking. Brakes front and rear would be eliminated saving weight in the process. Is this an impossible idea? In the meantime I'm following my idea. Wish me luck.


Electric motors can be run both as a forward mover ... and as a regenerative braking generator ... all in the same motor ... but not all motors do this equally well ... and not all motor controller do this equally well... some will not do it OEM ... and need to be modified.

It is usually a feature you have to look for ... and sometimes it costs more $ ... which then forces the question do you want to spend that $ on Regenerative braking ... more / better batteries ... better controller ... better motor ... etc... etc...

best of luck.


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## deanbo (Jun 7, 2010)

IamIan said:


> Agreed.
> A short list of a few reasons to have the regenerative braking generator disconnect.
> 
> #1> same reason you don't drive around constantly applying normal brakes... when you are trying to accelerate a generator that is trying to slow you down is counter productive ... when you are trying to maintain a steady speed a generator that is trying to slow you down is counterproductive... when you are going up a hill having a generator trying to slow you down is counter productive.
> ...


Thanks again IamIan. Regenerative disc brakes could only use electromagnets then? I thought it might also be possible to use permanent magnets if the calipers were kept far enough away from the disc rotor containing the copper coiling. 

Next question(s) would have to be(?) how powerful are the magnets that are required and how much more energy this would require from the battery not only in terms of the weight of the magnets but the amount of power required to magnetise them.


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## IamIan (Mar 29, 2009)

deanbo said:


> Thanks again IamIan. Regenerative disc brakes could only use electromagnets then? I thought it might also be possible to use permanent magnets if the calipers were kept far enough away from the disc rotor containing the copper coiling.
> 
> Next question(s) would have to be(?) how powerful are the magnets that are required and how much more energy this would require from the battery not only in terms of the weight of the magnets but the amount of power required to magnetise them.


A mechanism to move the magnets around seems overly complicated to me.

I think it would be cheaper and easier to just have something like a clutch disconnect the electric motor / generator when you don't want to use it... 

or it is much more common to design the system to have a variable load electronically , instead of mechanically ... so you can dial down the generator when not needed ... and dial it up when wanted.

for example ... the 10 kw IMA PM Brushless DC motor in my Honda Insight always turns when the ICE turns ... when I want regenerative braking or alternator action , I can on demand get up to ~5kw worth of power taken from the kinetic side as braking ... all the way down to about ~1,000 RPMs ... for as long as the BCM ( Battery control module ) lets me ... in the middle I can have it pull very little power at all ... like under 200 watts at 5,000 RPMs ... and when I want it I can get up to 10 kw of power added to the kenetic side ... so this motor has a variable load , controlled electronically ... even though it is always connected.

Permanent Magnets ( PM ) do not take energy from the battery to magnetize... this is sometimes a benefit of PM based motors.

Electro-magnets can also be used ... as you suspected they would take some energy to create their magnetic field ... but depending on the specifics of what you want from the motor ... sometimes that energy use can be justified by other gains.

You can make the project as complicated or simple as you like ... don't make it so complicated you end up feeling over whelmed and end up doing nothing... you could start with a small scale test to experiment with before scaling it up.

The variable load option can work well ... it just needs the system to be designed to do it ... so a motor, controller, etc... should all be designed to do regenerative braking... and if it is not your vehicles prime mover ... it would also have a 'free wheel' ... or near neutral option / mode as well.


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## Guest (Jun 19, 2010)

Use AC or get a SepEx motor and have regen built right in. AC best, SepEx next. Gives power and regen. No complex stuff. SepEx cheaper. Low power controllers so best for small light vehicles. Old VW's come to mind. 

Pete


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