Here's an idea I had.

What if you set up a turbine that is powered by magnets. I've seen magnet powered trains, I think in Disneyland or something, that were run on the resistance of magnets to each other. Using this idea, you could mount magnets on a turbine, and then surround it with magnets that push against them. If they are aligned at the right angles, they should spin the turbine that would generate electricity. Would this work?

No. This idea crops up from time to time. It won't work. The pat answer is that it violates the law of conservation of energy, (which it does). I know you probably won't find that satisfying so I'll try something a little more to the point.

Take two permanent magnets. Move them around each other, turn them this way and that, and so forth. Sometimes they attract, sometimes repell. Sometimes you will do work on the magnets, sometimes they will do work on you. The point of this excersize is that the laws of electromagnetism mandate that net work done by the magnets on you is at best zero for any repeatable "loop" of position and orientation. It can be less than zero (you do net work on the magnets) if for example you move the magnets near something conductive inducing eddy currents and generating heat. But the best you can do is zero.

So how does an electric motor work then? Well using an electromagnet in the motor you can creat nonzero "loops". (By varying the strenth of the electromagnet over time.) Guess what, the minimum electrical energy required to do this is equal to the "nonzeroness" of the loops. Kinda neat how energy is conserved, huh? ;)

i'll agree with kevin. and add the following.

electric motors work because of:
1. a rotating feild
2. by the use of a commutator

1. is employed in ac motors. by proper phasing the feild can be made to push the armature around

2. is used in dc motors and switches the feild at the right time to acheive the same effect as 1.

if you could replace one set of magnets, either the stator or the armature, with electromagnets then the turbine idea would work. but of course you would need to apply power to the electromagnets in the right phase.

it's been done already

it's been done already
links?

you do realize that dj is describing a perpetual motion machine don't you?

http://www.re-energy.ca/pdf/cp2.pdf

her's a DIY page on how to build your own hydroelectric generator.
It creates a current of electricity in a coil of wire using moving magnets

I think this is what he's on about? Either way turbines and magnets isn't new?
reread the op.
he is describing a setup that has pm magnets for both armature and stator.

the link you gave is the good old hydro-electric generator that is used at dam power stations

ohhhh, trying to reinvent the wheel

anyone here got a Levitron?

http://www.amasci.com/maglev/levtr1.html

"IT'S AN EXTRAORDINARY SIGHT -- a magnetic top spinning, bobbing and weaving in space for two minutes or longer. It remains levitated two or three inches above a larger base magnet. The top is not touching any other object, and no strings, electricity or other devices are used.

Levitation is one of mankind's oldest dreams, and it has now been achieved using just a few dollars' worth of ordinary permanent magnets and some pieces of plastic.


Anyone with even a casual interest in physics has to be amazed. For more than 150 years, such levitation was "known" to be impossible."

http://www.amasci.com/maglev/levtr1.html


this doesn't have anything to do with the op either

No. This idea crops up from time to time. It won't work. The pat answer is that it violates the law of conservation of energy, (which it does). I know you probably won't find that satisfying so I'll try something a little more to the point.

Take two permanent magnets. Move them around each other, turn them this way and that, and so forth. Sometimes they attract, sometimes repell. Sometimes you will do work on the magnets, sometimes they will do work on you. The point of this excersize is that the laws of electromagnetism mandate that net work done by the magnets on you is at best zero for any repeatable "loop" of position and orientation. It can be less than zero (you do net work on the magnets) if for example you move the magnets near something conductive inducing eddy currents and generating heat. But the best you can do is zero.

So how does an electric motor work then? Well using an electromagnet in the motor you can creat nonzero "loops". (By varying the strenth of the electromagnet over time.) Guess what, the minimum electrical energy required to do this is equal to the "nonzeroness" of the loops. Kinda neat how energy is conserved, huh? ;)


So the refute of this idea is in that you wouldn't be able to postion the magnets at angles that would keep the wheel spinning?

don't forget you also stipulated that electricity is to be extracted from this setup.

right, but the spinning of the wheel is the key to generating electricity, unless i'm mistaken.

you are correct. the spinning wheel is the key.
but you intend to extract energy from this device. where does this energy come from? if it comes from the device itself then you are describing a perpetual motion machine.

I don't know exactly how electricity is generated, but I'm thinking that the wheel being spun by the magnets is connected to like a drive shaft or something that would connect to whatever it is you spin to make electric

I don't know exactly how electricity is generated,
electricity can be generated in at least two ways
1. chemical (batteries)
2. a coil of wire moving in a magnetic feild

number 2 is our concern

you need to understand a few things about coils of wire.
when a coil of wire move through a magnetic feild the feild generates a current in the wire when a load is placed across the ends.
as soon as the current starts to flow it generates a magnetic feild
this second feild generates what is called a 'back emf'
this back emf will prevent the setup you describe from working.
it also explains why a generator is harder to turn the more current that is drawn from it.

So yeah, you connect a shaft from the spinning wheel that the stationary magnets create to an electromagnetic generator, or whatever you call it. If you need to seperate them so that they don't interfere with each other, then it will be a bigger setup than I planned, but wouldn't this still work?

And how does a coal burning plant produce electricity?

So yeah, you connect a shaft from the spinning wheel that the stationary magnets create to an electromagnetic generator, or whatever you call it. If you need to seperate them so that they don't interfere with each other, then it will be a bigger setup than I planned, but wouldn't this still work?
no. electricity is energy. in order to extract energy from your setup the back emf will prevent it unless energy from outside the system is applied.

how coal is used to produce energy.
one word, steam
coal is used to heat water to the boiling point and beyond.
the steam that is produced is channeled through the turbine blades to rotate the generator.

but if you seperate the two magnetic fields, by way of a huge lead wall, or whatever you have to do, then how is the wheel powered by magnets any different than steam in turning the generator?

there is no known substance that can block magnetic feilds.

the difference between your setup and a coal fired setup is that the energy required is supplied from outside the system namely coal

in your system as soon as you start to draw current from generator a back emf will be produce. additional energy must be supplied to countract the back emf.

Ok, well could you put them far enough apart that they don't affect one another? I know that magnetic fields don't range forever, otherwise all metal would be attracted to the closest magnet.

Ok, it's clear that there is something you don't know about generators. Unloaded, they spin relatively freely, ignoring bearing friction and the like. But as soon as you start to draw current from the output terminals, a drag is induced in the rotor. It gets harder to turn and starts to slow down. You have to supply energy (mechnical work) to the input shaft to prevent it from slowing to a stop. And of course the best you can do is for the electrical output to equal the mechanical input.

Ok, well could you put them far enough apart that they don't affect one another? I know that magnetic fields don't range forever, otherwise all metal would be attracted to the closest magnet.

What the man is trying to say, DJ, is that yes, presumably, you could spin a wheel with magnets (perpetually, assuming a perfect system - no friction or other drag forces).

However, as soon as you draw a current from that system, you introduce a drag (back emf). Your wheel will start to slow down, unless you either help it by turning a crank, or introduce additional magnets.

It is irrelevant how far apart the magnets and the generator are placed, physically. They must be connected (by means of a drive shaft), and that shaft will transfer the drag forces between the two points (just as it transfers the productive forces).

Actually, that's not back emf. Back emf is the voltage that is induced in a motor's windings opposite to the drive voltage. This limits input current and is an aspect of a motor's efficiency. It also occurs in transformers and other coils and is why a well designed transformer draws little current from the line untill a load is drawn.

there is no known substance that can block magnetic feilds.Iron can. For example, there is a 7 Tesla MRI machine at NYU that I have used. It has to have something like 600 tons of iron plates around it. The plates are there for one purpose only, to keep the magnetic field from pulling on or magnetizing things outside the room. Iron is not terribly effective at it, which is why 600 tons are needed. Basically it works by the little magnetic subdomains in the iron becoming aligned opposite to the machine's field and cancelling it out.

This doesn't negate your comments about how generators work and require external energy. The OP could use his idea as a magnetic bearing, to passively reduce wasted energy, but not as a generator to actively produce energy.

-Dale

there is no known substance that can block magnetic feilds.


Just as a point of interest, I have worked with mu-metal many times to shield sensitive military magnetometers in various test setups. It has an extremely high permeability and can effectively shield against static or reasonably low frequency magnetic fields.

Ok, it's clear that there is something you don't know about generators. Unloaded, they spin relatively freely, ignoring bearing friction and the like. But as soon as you start to draw current from the output terminals, a drag is induced in the rotor. It gets harder to turn and starts to slow down. You have to supply energy (mechnical work) to the input shaft to prevent it from slowing to a stop. And of course the best you can do is for the electrical output to equal the mechanical input.You are correct here and in other post about back EMF (which rather than be created is reduced to let the current flow, as you basically said) I just want to mention an old (more than 50 years) illustration of the above, never to be used again, now that we have transistors etc.

There existed just after the war, a military motor / generator (WWII's "PE 103" - God only knows why the number still sticks in my head when so much has fallen out.) quite cheap surplus unit with at least a few hundred watts capacity. Back then "tubes" were the only way to make a radio, and they required a few 100 volts of DC (the B+ or "plate voltage")* to work which was not available in a jeep (or car) but 6V was from the vehicle battery (12V batteries came later) The PE-103 had one shaft, one end of which was a 6V DC motor and the other was a 500 Volt DC generator so that unit served as a DC to DC voltage converter. I had one in the truck of my car (actually my father's car) and a moble amateur radio transmitter (single "807 tube" as final RF stage was driven by a "6L6" tube - why is my memory space retaining this crap?).

One day we nearly wrecked the car as we got so excited when our "CQ" (= calling anyone or phonetically approximately "seek you") just transmitted on 10 meters was answered by a "ham" in Cuba.
---------------------------------
It was the "B+" as the "A+" was the first battery you had to turn on to heat up the filaments.

Iron can. For example, there is a 7 Tesla MRI machine at NYU that I have used. It has to have something like 600 tons of iron plates around it. The plates are there for one purpose only, to keep the magnetic field from pulling on or magnetizing things outside the room. Iron is not terribly effective at it, which is why 600 tons are needed. Basically it works by the little magnetic subdomains in the iron becoming aligned opposite to the machine's field and cancelling it out.

This doesn't negate your comments about how generators work and require external energy. The OP could use his idea as a magnetic bearing, to passively reduce wasted energy, but not as a generator to actively produce energy.

-Dale

I can't see how a ferromagnetic material would develop magnetic domains opposite the direction of the applied magnetic field. I would think that the mechanism would be "completing the circuit." The field follows the shielding around from one end of the magnet to the other as the most attractive path, a path of negative resistance.

Actually, that's not back emf.
then what makes a generator harder to turn the more current that is drawn from it?

then what makes a generator harder to turn the more current that is drawn from it?
leo,

I think kevin is being a bit picky with the words. The back EMF (a voltage) technically causes a current to flow that generates a magnetic field that opposes the driving field. Yes? My Motor-Gen theory is pretty old...

leo,

The back EMF (a voltage) technically causes a current to flow that generates a magnetic field that opposes the driving field. Yes?
yes, that's right.

I can't see how a ferromagnetic material would develop magnetic domains opposite the direction of the applied magnetic field.Don't you remember the old addage "opposites attract"? This is exactly what inspired that saying. The North poles in the iron domains line up to the South poles in the MRI magnet, thereby canceling out some of the field.

Don't forget that a magnetic field contains a certain amount of energy. As they are installing these iron plates the field does some work on the plates. The plates are pulled towards the magnet as you might expect based on your own experience with iron and magnets. This work also aligns the subdomains so as to reduce the magnetic field. The work done by the field on the subdomains is equal to the energy lost by cancelling the field. Fundamentally, that is why opposites attract, because they cancel out the field and reduce the energy associated with the magnetic field.

-Dale

I have worked with mu-metal many times to shield sensitive military magnetometers
http://www.physlink.com/Education/AskExperts/ae512.cfm

http://www.physlink.com/Education/AskExperts/ae512.cfm

...Do this by shielding the object in a material with a much higher magnetic permeability of the surrounding materials.

Exactly. mu-metal.

http://metals.about.com/library/bldef-Mu-Metal.htm

http://en.wikipedia.org/wiki/Mu-metal

http://www.mumetal.com/

What you describe are opposite poles, but in order to attract, the magnets have to be oriented roughly the same direction. When you magnetize an object the magnetic field of the magnetized object is the same direction as the applied field. You and I may be describing the same thing while talking past each other. What happens to the "direction" of the field when it circles around to meet itself again? This is why if you set two magnets side by side facing the same direction they repel each other.

I think that the major mechanism here is that the magnetic field lines are coerced to follow the iron surrounding the magnet so that they do not do what they naturally do, and that's spread out. We can call that creating domains that repel the field or something like that, but that is what I think is happening.

I have a pair of cheap supermagnets that I got from Radio Shack. They seem almost able to pull a wood screw through wood from the other side. An interesting thing here is that I have not been able to find a piece of stainless steel or brass in the entire house that won't stick to them. I don't have any metallic bismuth or I could try something else.

I may have been a bit picky. Sorry. My point is that back emf usually refers to an inductively induced voltage that limits current. This doesn't happen significantly in a generator. Back emf and generator drag do arrise in a similar fashion. The induction law that states that induced currents appear in such a way as to oppose the magnetic field change that produced the currents.

No prob kevin. I knew what you meant.

I thought superconductors expelled magnetic fieldsd from their interiros, and thus a cage of it couldbe used as a magnetic shield?

http://www.sciforums.com/showthread.php?t=47314

Iron can. For example, there is a 7 Tesla MRI machine at NYU that I have used. It has to have something like 600 tons of iron plates around it. The plates are there for one purpose only, to keep the magnetic field from pulling on or magnetizing things outside the room.


You sure theyre not there to cut down on EM interference?

I heard the idea doesn't generate enough energy anyway, sort of like elect induction