electro magnet help and advice

Discussion in 'General Electronics Chat' started by black01, Jun 11, 2013.

  1. black01

    Thread Starter Member

    Jun 10, 2013
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    I built a electro magnet and I did things a little different than I have seen most people do it. I would like to describe how I built it and what the thought process I had was and see if I was anywhere close to correct. so what I did was take a small iron pipe with about a one inch ID and fill it with small iron rods and wrapped that with about 100 turns of 18 gauge automotive wire. I then took a bigger pipe and wrapped it with 100 turns of wire I did this with 4 different pipes all getting progressively bigger. I then put one inside the other and wired them all up in series using one side of the inside pipe as one pole and the opposite side of the outer pipe as the other pole. I used a 525 cranking amps car battery and wired a potentiometer in circuit. my thought was that the inner magnetic field would be amplified by the one around it and the one around it would amplify the one around it and so on and so on making the magnet stronger. when I turned it on it was very powerful it drug a 8 inch pipe wrench across the table from about a foot away but I could only have it on for a short time before the wires started to melt. the magnet is about 8 inches long and has about 5 inch OD it weighs about 8 pounds. the problem is I don't know if I have wired it up correctly or if there are any other things I could to do to make it more powerful. any thought on how to make my magnet better or if my thought about building the magnet the way I did was correct any help would be appreciated thank you in advance.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You may be better using a Constant current supply as opposed to a high voltage one, your coil windings may be too low in resistance to take the current required to produce the magnetic strength.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    It seems to me that one would obtain the same result by simply winding the same total number of turns (with DC excitation), albeit as a multilayer winding on an iron core rod of the same dimensions as the outermost pipe.
     
  4. black01

    Thread Starter Member

    Jun 10, 2013
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    I have herd of very powerful electro magnets built by amplifying one field with another I just don't know the details on how to build it or exactly how it's suppose to work
     
  5. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Magnetic fields do no amplify, they just add. This is a basic property of e and m fields, and makes them pretty simply mathematically ( as compared to things that do not add ). See superposition.
     
  6. black01

    Thread Starter Member

    Jun 10, 2013
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    Well here's another question is there another way to generate a powerful magnetic field that is better than building a electro magnet
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  8. bance

    Member

    Aug 11, 2012
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    Dem mushrooms:D
     
  9. black01

    Thread Starter Member

    Jun 10, 2013
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    well I don't think I need to be setting off any nuclear bombs lol and I want a field I can keep on for a while. im thinking I should wire all my sections in parallel so there is 12 volts to all four sections. im sure im wasting my time its just something I was curious about and figured I would experiment to see what would happen. I think I need better wire too with a thinner insulation so I can get more turns in the same amount of space. does anyone have a good wire they use that would handle the current im putting through it and that could tell me where I can get it
     
  10. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The wire you want, is called (drum roll) magnet wire.:) The cheapest place I've seen it is on Ebay.
     
  11. eKretz

    New Member

    Apr 21, 2013
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    You're going to need some serious wire if you want to run over 500 amps through it for any length of time. Water cooling might be a thought to consider, but it could be dangerous, so maybe you'd better not try it. The heat buildup will reduce your magnetism as it increases.
     
  12. Austin Clark

    Member

    Dec 28, 2011
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    Producing multiple coils and connecting them in parallel is the same as using one coil of thicker-guage wire.
    In general, using thinner wire, higher voltage, and more coils is best.
    I've found that keeping strong electromagnets cool is the hardest part.
     
  13. black01

    Thread Starter Member

    Jun 10, 2013
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    What gauge would you recommend
     
  14. eKretz

    New Member

    Apr 21, 2013
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    Well, how long are your coils? You need to take the length into account to avoid voltage drop and more heat buildup. Any way you look at it you're talking a cubic ****-ton of wire if you want to run 500 amps. Check out this chart for a general idea of what you're looking at:

    http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html
     
  15. black01

    Thread Starter Member

    Jun 10, 2013
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    So what your saying is get a smaller power source. What's more important to make a strong magnet volts or amps
     
  16. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    More turns of wire.
     
  17. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    The strength of the magnetic field produced by such an electromagnet depends on the number of coils of wire, the magnitude of the current, and the magnetic permeability of the core material; a strong field can be produced from a small current if a large number of turns of wire are used.

    You simply use Ohms law and a chart of wire gauge resistance for copper wire. You can select the wire gauge you need based on the current you plan to use and the strength of the field you must create.

    If you choose a design with an excessive number of layers of wire those wires in the center will not have access to free air flow and will heat up very fast, which is often why several smaller coils are connected in series with gaps in between for access to air flow.

    a core which tapers to a smaller diameter at the end can create a 'stronger' magnetic field at that point than one which maintains the same diameter from end to end. The trick is to know the 'break even' point for the magnetic material you are using for the core. As the number of lines of magnetic force per unit area increase, the magnetic material becomes less responsive to each additional 'ampere-turn' of wire. It's kinda like how gas mileage works in an engine. The closer the RPM's and horse power get to the motors maximum the less responsive the motor becomes to further increase. Likewise the more magnetic field strength you create in a given material the less responsive that material is to a further increase of energy input. Eventually you reach a 'saturation' point and no further increase of electrical energy will produce any increase in magnetic field strength.
     
  18. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I have attached a 7 page excerpt from an older text on coil winding, it contains a very good example of a design for a specific field density with a wattage requirement(heating limit). It will show you how to correctly design a coil for a specific given voltage, current, and strength.
     
  19. black01

    Thread Starter Member

    Jun 10, 2013
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    Thanks guys I'm also thinking about leaving a big enough gap to set up some kind of cooling system between each layer of the magnet and maybe using a dry ice and alcohol mixture to pump through the layers so I can put more amperage through my wire and also playing with my core to find something with more saturation does anyone know of something that is pretty easily available
     
  20. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Does what your building need to be cylindrical? If you take an old microwave oven transformer apart you could use the lamination's from that. Using just the "E" lamination's also gives a better magnet, because both poles are available that way. The lamination's are made of a special steel, formulated to have a high saturation rate.

    In case you don't know what 'E' lamination's are, most transformers are made of 'E' and 'I' pieces. They alternate in the stack-up of the transformer core. If you put all of the 'Es' pointing one way you have an 'E' core. The center leg of the 'E' will be one magnetic pole and the two outside legs will be the opposite pole. This (in a square shape) is how lifting magnets in a scrap yard are made. But the scrap yard magnets are round. Same principle though.

    If you already knew the above, I meant no offense for explaining. Just trying to help.
     
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