Power generation from passing metal objects? 1

[CSLufkin]

O.K., I'm not en EE, but I have a question for you guys and I'm sure it goes way back to the basics for you but please bear with me. What would you need to do to generate Electricity from a passing metal object? Similar to the way a linear motor works, but in reverse. I know you can use a linear motor to stop something and turn that energy into heat. How could it be turned into Electricity? Could it be prototyped cheaply and easily?

 

[Skogsgurra]

That's the way most generators work. The metal object is iron with a magnetic field. Sometimes it moves in a circular path (generators) and sometimes in a linear path (as it usually is in maglev trains and other linear motors). It is really difficult to answer your question. It is very general.

Gunnar Englund

http://www.gke.org

 

[IRstuff]

Which object? One of your choosing or a random one?


You need a field moving across a wire to generate. One object, stationary or moving, must be the coil of wire that actually generates the EMF and current. The other must generate the magnetic field, stationary or moving.

TTFN

 

[CSLufkin]

O.K., O.K sorry I was so vague before, but I get a fleeting thought and I need to spit it out before it vanishes.
I will probably never follow thru so I will throw out my big briliant idea (Please remember me when one of you gets rich off it). What I was thinking of was generating electricity from cars passing over a field that is built into a roadbed. They could be used on hills or near intersections where cars are braking anyway. It seems like a viable idea, has anyone heard of it? Would there be any problems with childrens bikes or old ladies walkers being sucked onto it?
I would love to prototype it with a toy car, I could be like the wierd guy on Back to the Future. Flux Capacitor anyone? Maybe we can get a few Jigawats out of it.

 

[Skogsgurra]

Or a jigsaw puzzle?

Gunnar Englund

http://www.gke.org

 

[sreid]

I saw on TV a system where mechanical "Bumps" at stop lights extracted power from stopping cars.

 

[jghrist]

Save the environment! Run red lights!

 

[jraef]

CSLufkin,
All kidding aside, the answer to your question is NO, you cannot extract energy from regular cars moving over a surface. Not without having the cars fitted with very powerful generators and electromagnets, or extremely large permanent magnets. Of course, then you are just shifting the power production (or consumption) to the car. As IRStuff said, it is not just moving metal that generates power, it is moving magnetic fields.

http:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[waross]

I think that it is theoretically possible but not feasible due to the extremely low efficiency.
Let's consider what modifications would have to be made to a linear induction motor in order to extract energy from passing vehicles.
The synchronous linear speed of a linear induction motor depends on the applied frequency and the spacing of the coils.
When the linear speed exceeds the synchronous speed regeneration is possible.
One type of transit linear induction motor (about 400 Hp.) uses a steel strip about 10 inches wide and 1/2 inch thick covered with a strip of alumunum about 1/8 inch thick. This is called the LIM rail.
The alternating magnetic field induces eddy currents in the aluminum strip, analogous to the currents in the squirrel cage in a conventional induction motor.
The steel of automobile bodies would most likely be much less effective at concentrating the magnetic field because of the much lower cross section. This efficiency may be less than 5%.
Without the aluminum skin to produce eddy currents and the resulting magnetic fields, we will have to depend on eddy curents in the surface of the steel to produce the interacting field. Again, the efficiency may be less than 5%.
We now have a possible combined efficiency of 5%x5%=0.25%.
Now consider the spacing.
The clearance between the coils and the LIM rail is much less than an inch, 0.025 of an inch is a reasonable guess.
Suppose that the effective steel of the automobile is 5 inches above the roadway. That is a ratio of 5/.025=200 to one. The magnetic field will fall off as the inverse square of the distance, so we have 1/(200)^2=0.000025, or 0.0025% efficiency of the magnetic field.
Our overall efficiency looks like 0.25% x 0.0025% = 0.00000625% or one part in 160,000.
Even if my efficiency estimates are out by a factor of 1000, the usable energy is not enough to supply the losses.
Furthermore, the biggest factor in the estimations is the air gap ratio. The error here will probably be less than a factor of 10.
I suspect that the other efficiencies may be less than my estimates.

It was a good question, I hope this is a good answer.
respectfully

 

[IRstuff]

First of all, it's not free energy, so let's get that out of the way from the get go. In order to generate power, you need to steal power from each passing car. Since that means that you are effectively generating electricity from the burning of gasoline and using a very inefficient approach, the net result is more greenhouse gases and more gasoline consumption.

So, in general, in order to extract power from each passing car, you must effectively induce a drag force on each car. How that's accomplished, I don't know and for the purposes of the discussion, I don't care.

Assume each car goes by at 60 mph over a stretch of road and you only cause a decrease in speed of 5 mph. Assume each car weighs 3000 lbs. The net result is that you can cause a net decrease in energy of the car of 21 Wh. Let's say that the net efficiency is 10%, so you only get 2.1 Wh per car. The 10% is to account for the efficiency of the drag induction process in extracting kinetic energy coupled with the conversion of that energy into usable electricity.

Assume it's a 2-lane trap with cars passing every 6 seconds. The net result is 62 kWh per day, which is enough to feed 3-5 houses in the summer time. But the cost is quite exhorbitant, since the net generation efficiency from the gasoline is only about 3%.

At a base rate of 3 cents per kWh, you get $1.86 benefit per day or about $49/month of benefit. If the amortized cost per month exceeds $50, which it probably will, you'll never break even and you'll be causing about $11 of cost on the passing cars per month.

TTFN

 

[IRstuff]

Slight error on the cost side, it's $107 of induced gas costs per month on the passing cars.

TTFN

 

[jraef]

Waross,
Interesting thought on the disimilar metal / eddy current concept, I learned something today.

IRStuff,
In spite of waross making it all a moot point, the OP did say "where cars are braking anyway", such as on hills (assuming down hill) or intersections. In that case, the additional drag would actually be a benefit to the cars, not a fuel burden. Good point otherwise.

http:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[MikeHalloran]

The part of the problem that makes the idea impractical is air gaps.

Just as there must be a continuous conductive loop in which electricity can flow, there is an analogous magnetic circuit that forms a closed loop.

The problem is that air gaps must be present, and the magnetic analog of current is extremely sensitive to them, because they present a very high magnetic 'resistance'. In a small electric motor, the air gap might be 1 mm. In a utility hydro generator, the air gap might be 10mm, but the magnets are very strong. Because of ground clearance and suspension dynamics, the air gap under a car would have to be 10cm or more. The car couldn't carry a magnet powerful enough to usefully energize a wire through an air gap that big.







Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

In my opinion, CSLufkin should have let this idea vanish. Qoute from his posting: "I get a fleeting thought and I need to spit it out before it vanishes". Please don't spit in here!

As I said a few times before; we try to keep a certain standard in these fora. That is part of the site policy and that is why this site works as well as it does. That is also why engineering topics are discussed and perpetual motion, free energy and other discussions are banned from the site.

CSLufkin is obvious not an engineer. He has got one of those "brilliant ideas". That was very clear from the beginning. Spelling Gigawatt as Jigawatt is a sure sign that he never opened an engineering book - but he may have heard "Jigawatt" on Discovery. The idea of getting Gigawatts out of a system that usually is on a 100 kW level - at most - is another sign that we are dealing with some mild sort of "mad inventor".

I feel sorry every time themes like these get an undeserved honest treatment. Better kill it with irony. Or ignore it. Or RF it.

Gunnar Englund

http://www.gke.org

 

[CSLufkin]

Thanks Skogs, your a sweetheart.

 

[Skogsgurra]

Yes. I am.

Gunnar Englund

http://www.gke.org

 

[CSLufkin]

For some reason (usually arrogant people don't bother me) I feel like I need to defend myself and my "Brilliant Idea".
I am a Mechanical Engineer, I work in Tooling and Automation. Perhaps not up to your brilliant standard, really just a pretty ordinary guy, but an Engineer just the same.
My idea stemmed from a conversation I had with a friend about the ammount of energy wasted by the braking system of a car, turning motion into heat. We wondered if you could slow them with a magnetic field and turn that motion into Electricity. JRAEF pointed out the fact that I mentioned these "generators" being near intersections and on hills (Yes I did mean down grades).
Mad inventor is exactly what I was going for. If you had taken the time to read the post you would have seen a reference to a movie line which indeed was Jigawats, its called a sense of humor, try it sometime. Next time maybe I will add one of those little smiley face guys.
My appologies to you all if my original post was not clear or specific enough. I will try not to waste all your time in the future. Thank you to those of you who were helpful. Something else to he who wasn't.

 

[Skogsgurra]

The recuperation of braking energy is done in vehicles with electric motors. It is by no means a new or unknown technology. Only it is done using sound engineering principles and no mad inventor pipe dreams.

You cannot expect to be taken seriously if you didn't even do some basic research (googling, for instance) before presenting your thoughts and telling us to remember you when we get rich from it. Thoose brilliant ideas are so common that they are invented tens or hundreds of times every night in pubs all over the world.

Gunnar Englund

http://www.gke.org

 

[sreid]

While I also believe that this idea is impractical, one could induce a voltage in a coil through the changing reluctance of a steel auto passing over the poles of a permanent magnet.

 

[itsmoked]

I don't think that would work sreid! The car's distance would be too great as the bicyclists pinned to the permanent magnet would cause excessive clearance issues.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com