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Thread: What is homo-polar generator?

  1. #1 What is homo-polar generator? 
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    I would like to know about homo-polar generator deeply... can someone hep me out with some informations???


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    Brassica oleracea Strange's Avatar
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    I had never heard of this before.

    Homopolar generator - Wikipedia, the free encyclopedia

    Do you have any specific questions?


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    ei incumbit probatio qui dicit, non qui negat
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  4. #3  
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    is it a kind of an electrical generator??
    Last edited by elecate; December 9th, 2013 at 04:13 AM.
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  5. #4  
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    Quote Originally Posted by Strange View Post
    I had never heard of this before.

    Homopolar generator - Wikipedia, the free encyclopedia

    Do you have any specific questions?
    what is the different between this generator with others?
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  6. #5  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by elecate View Post
    is it a kind of an electrical generator??
    Yes. It generates a DC (direct current) voltage. Typically, a low voltage but they can generate a high current.
    ei incumbit probatio qui dicit, non qui negat
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  7. #6  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by elecate View Post
    what is the different between this generator with others?
    There are many different types of generators. There is a summary here:
    Electric generator - Wikipedia, the free encyclopedia
    ei incumbit probatio qui dicit, non qui negat
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  8. #7  
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    i had been asked by my teacher to make a research about this, can you give me some idea??
    is it about how to generate high current with homopolar generator???
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  9. #8  
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by elecate View Post
    what is the different between this generator with others?
    There are many different types of generators. There is a summary here:
    Electric generator - Wikipedia, the free encyclopedia
    i had been asked by my teacher to make a research about this, can you give me some idea??
    is it about how to generate high current with homopolar generator???
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  10. #9  
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by elecate View Post
    what is the different between this generator with others?
    There are many different types of generators. There is a summary here:
    Electric generator - Wikipedia, the free encyclopedia
    i had been asked by my teacher to make a research about this, can you give me some idea??
    is it about how to generate high current with homopolar generator???
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  11. #10  
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    Quote Originally Posted by Strange View Post
    I had never heard of this before.

    Homopolar generator - Wikipedia, the free encyclopedia

    Do you have any specific questions?
    i had been asked by my teacher to make a research about this, can you give me some idea??
    is it about how to generate high current with homopolar generator???

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  12. #11  
    Brassica oleracea Strange's Avatar
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    As I say, I have never heard of it before so I don't know anything more than is on the Wikipedia page. If there are things on that page that you don't understand, then maybe I can explain them to you.
    ei incumbit probatio qui dicit, non qui negat
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  13. #12  
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    Quote Originally Posted by Strange View Post
    As I say, I have never heard of it before so I don't know anything more than is on the Wikipedia page. If there are things on that page that you don't understand, then maybe I can explain them to you.
    ok, so can you explain to me what you understand about what is on the wikipedia?
    Last edited by elecate; December 13th, 2013 at 12:08 AM.
    Knowledge is precious,so appreciate them..
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  14. #13  
    Brassica oleracea Strange's Avatar
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    [QUOTE=elecate;499659i had been asked by my teacher to make a research about this, can you give me some idea??[/QUOTE]

    Quote Originally Posted by elecate View Post
    ok, so can you explain to me what you understand about what is on the wikipedia?
    I see. So you are looking for someone to do your homework for you. No thanks.

    Read the article. If there are things you don't understand, then ask a question. Perhaps someone will help. (But not me.)
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  15. #14  
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    A Homopolar Generator is an electric generator that produces a dc current by spinning a conductive disc in a magnetic field. The magnetic field induces a radial voltage across the disc, in direct proportion to the distance the charge travels, namely from where the circuit connects near the axle and near the rim of the disc. The current produced is entirely dependent on the amount of kinetic energy available to be turned into electrical energy via a current forced through the circuit. I will not give you equations or specific information for this, as that is something you should research, and depending on the depth of your homework, experiment with yourself.

    I have done a lot of research into homopolar motors (I'm a personal proponent of homopolar motors), and it definitely pays to do the research yourself, as opposed to having someone tell you all the information. And all a generator is is a motor run in reverse action, where a motor turns when a current is applied to the stator/rotor, and a generator produces an electric current in the stator/rotor when a torque is applied
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    Hi Arcane Mathematician,

    I anm fascinated by homopolar motors and have an esoteric project for a generator. However, their Achiles' heel is the brush friction.

    Can you give please me an explanation of why the brush cannot be obviated (if it can't be)?

    John.
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    Hi Arcane Mathematician,

    I am fascinated by homopolar motors and have an esoteric project for a generator. However, their Achilles' heel is the brush friction.

    Can you please give me an explanation of why the brush cannot be obviated (if it can't be)?

    John.
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  18. #17  
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    Quote Originally Posted by John Mack View Post
    Hi Arcane Mathematician,

    I am fascinated by homopolar motors and have an esoteric project for a generator. However, their Achilles' heel is the brush friction.

    Can you please give me an explanation of why the brush cannot be obviated (if it can't be)?

    John.
    Well, if you read up on how a homopolar generator works, you would know that the voltage is induced between two points on a rotating disk. So, you need to make electrical connections to a thing that rotates. If the load to be driven is not also rotating, then you have the problem of making an electrical connection between a rotating thing and a stationary frame. I don't know how to do that without using brushes (or the equivalent thereof).
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    I am familiar with conventional homopolars. What I am exploring is the possibility of bringing the outer contact back to shaft diameter
    via conductors embeded in iron, perhaps.

    What is not clear to me is how to relate homopolar generation with conductors cutting flux! Whilst the disc rotates, the path between centre and outer brush is radial and so is stationary in the magnetic field. Therefore, the current path is not cutting flux. Even the rotating disc can be rotating between circular poles so does not experience a changing flux like a 2-pole dynamo does.

    I'm missing something!
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  20. #19  
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    Quote Originally Posted by John Mack View Post
    I am familiar with conventional homopolars. What I am exploring is the possibility of bringing the outer contact back to shaft diameter
    via conductors embeded in iron, perhaps.
    Sadly, that won't work. You will induce an exact counter-emf in the embedded conductor, so you won't get any net output.

    What is not clear to me is how to relate homopolar generation with conductors cutting flux! Whilst the disc rotates, the path between centre and outer brush is radial and so is stationary in the magnetic field. Therefore, the current path is not cutting flux. Even the rotating disc can be rotating between circular poles so does not experience a changing flux like a 2-pole dynamo does.

    I'm missing something!
    Ah, yes, indeed you are. Your question is a great one, and in fact is known widely as Faraday's Paradox. The paradox arises from an incomplete accommodation of all the flux paths (or, alternatively, the surfaces traversed by the flux lines). If you do the calculation correctly, the paradox disappears.

    That said, you can avoid the paradox by carrying out an analysis based on the Lorentz force law instead.
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  21. #20  
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    Okay. Bringing the conductor of the outermost part of the disc back to the diameter of the shaft is most certainly possible, and the generator/motor will still work. The problem is, as tk421 stated, you'll have some wicked nasty back emf that will be almost the same magnitude as the driving force, depending on position in the magnetic field. Essentially, it will cut the effeciency by around 50-90%.
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  22. #21  
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    But what if you bring the wire from the outermost part of the disc to the shaft center from inside the disc itself + enclose the wire in a screen type of shield like microphone or acoustic cables and then ground the shield or etc.?
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    Thanks. I'm bogged down for a while. Lorenz is helpful in explanation to a degree but I am missing insight - and into the paradox. I'll seek more advice, soon.

    John.
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  24. #23  
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    Quote Originally Posted by Crazymechanic View Post
    But what if you bring the wire from the outermost part of the disc to the shaft center from inside the disc itself + enclose the wire in a screen type of shield like microphone or acoustic cables and then ground the shield or etc.?
    This works, kind of. Using a magnetic shielding material will help keep on direction of force smaller than the other, but it will also add weight. Extremely strong magnetic fields aren't drastically reduced by shielding, unless it is quite massive. Thin shielding, like whats in stereo cables, won't reduce the field strength a significant amount before it hits the wire. You're looking at a 1-10% reduction in field strength, and to be worth the the difference in friction, you'd need a much more drastic reduction in magnetic field strength. In order to get that reduction, you'd need centimeters of shielding around the wire, which is very impractical on the small scale, and on the large scale liquid metal contacts are already a viable and used option, with many benefits over shielding.
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    ok, but what if I make my faraday disc of a pretty thin copper metal but with an empty middle and the return wire goes in the middle ad the side plates are further away from the middle return wire , a magnetic field can be strong but it obeys the law under which it falls of with distance , inverse square law , so the discs being further apart and the return wire in the middle should drastically reduce the opposite fields messing each others ways? what do you think?
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    Remember that magnetic field lines ALWAYS form closed loops. Every part of your return wire will still be subject to force, no matter how long or far away it goes. If your return path is 10 times longer than the initial travel path, while it won't be the same opposing force, it will be experiencing less of the opposing force for a much larger distance.
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