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Electromagnetic induction Coil testing

  1. Sep 1, 2009 #1
    Whats the easiest way to test the max output of electricity induced in an air coil.
    I will wire it 3 phase delta. (or double delta) Will I need a resistive load attached for current flow? What should I use? How do I test? Use a multi tester? Is there math I can use to estimate the amount. I tried E = B times v times l. Flux in Tesla, velocity in M/s and l in meters. So E = 23.4T X 37.5 M/s x 675M =86,062.5 Volts? How do get amps? I want maximum amps. Is there a trick? This is not hypothetical. Ive built this generator. I 'd like to get 550 volts at 100 amps. Possible? Any help would be great. Thanks Magnetic-man
  2. jcsd
  3. Sep 2, 2009 #2


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    Maybe you could explain what you are doing?

    You have an air coil 675 M long (that's about 0.4 mile) and a field of 23.4 tesla (that's about 1 million times the earth's magnetic field) and something moving at 37.5 m/sec (that's about 84 MPH).

    And you have actually built this?
    Last edited: Sep 2, 2009
  4. Sep 2, 2009 #3
    Yes. The coil uses 675m of #18 copper wire. 3 sets of 5 (total 15) very powerful N50 Neodymium magnets. One set is 5@18,800 Gauss each & having 650 lbs of pull force each Total 94,000 Gauss=9.4T A second set is 5 @13,300 Gauss and 210lbs of pull force each Total 66,500Gauss =6.7T A third set of 5@ 14,700gauss and 430Lbs of pull force each Total 73,500 Gauss=7.4T Total magnetic strength or B= 23.5T
    They rotate at 3500 PRM proximate to the 675M of copper wire. The coil is curled into a toroidal so It can be continuously encircled in one direction. The magnets rotate 1/16 inch away from the outermost layer of wire. The third set is actually inside the toroidal vessel core and are "dragged" around inside by the coercive force or the exterior magnets. Yes its built. I'm waiting to wind the toroid with the wire until I get some advice on the most effective method of winding it and wiring it. I want it to generate enough volts and amps to run a small office for instance. Ive researched many different methods of wrapping the Troidal core. Another guy on here Berkeman, suggested breaking the coil into smaller sections. None longer than each magnetic face. I know in a toroidal all the "Lenz effect" is directed inwardly. This is why the toroidal is used in electronic equipment, because its almost self shielding and does't affect other devices on the board. I originally designed it to run electric vehicles and specifically my electromagnetic piston motor. But those who looked at it so far have said it should have power to spare. My R&D money is very limited so I'm only going to get one shot at wiring this thing right. Thats why I'm asking for help from you geniuses. I don't know how to test it since the current wont be smoothed or rectified or at any hertz frequency. Just raw power. Any advice? Magnetic-man
  5. Sep 2, 2009 #4


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    So, where does the power to rotate the magnets come from?
  6. Sep 3, 2009 #5


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    Thanks for the explanations via Private Mail, but please don't do that.

    Do you know what happens if you drop a short magnet down the middle of a long solenoid?

    Once the magnet is inside the solenoid, the two poles generate equal and opposite voltages in the solenoid. So, you get zero or a very small voltage out.
    Now, can you see how this affects your design?

    You can measure the voltage across a solenoid with a voltmeter provided it is AC and of sufficient rating. You can also use an oscilloscope which may be better but would be more expensive. For current, you would have to find a suitable resistor that would not overheat.

    Using batteries to drive a motor to drive a generator is generally an inefficient way of generating 550 volts at 100 amps.
  7. Sep 16, 2009 #6
    I have been researching magnets and coils because I want to build a wind electric generator.
    I have discovered some things that may help.

    I don't think you can use the number of Tesla's you mention.
    BrMax is the strength of the magnetic field in the center of the magnet material.
    For closer to real world calculation you need "surface gauss".
    It is the surface gauss strength that will directly affect the coil. The air gap between magnet and coil also matters.

    KJ Magnetics lists the Surface Gauss for most magnets. Discs tend to have a stronger SG than a block magnet at the same thickness. Example specs

    Faraday's Law is the next stop.
    Volts=#Turns X surface gauss in Tesla's X Area of the coil in square meters / The speed at which the magnet moves into a coil. As it moves out it will generate the opposite polarity, creating a sine wave.

    You state magnets 5 @ 13,300 with 210lb pull force.
    My guess is the surface gauss is about 6,400, converted to Tesla's is .64T.

    The Tesla's are not additive in a normal coil magnet configuration. And Magnet size and strength usually stays constant, not multiple size magnets. So, whatever the strength of 1 magnet is the # of Tesla's for calculations.
    The stronger the gauss the more energy and current that will be produced.
    For instance:
    234 * .3T * .0067 m^2 (10.5 square inches) / .3 seconds (200rpm) = 1.568 Volts
    Approximate length of the wire in the coil is 705 feet for 1.7625 Ohms.
    1.568V/1.768Ohms = .89 Amps
    Double the gauss only.
    234 * .6 * .0067m^2 / .3 = 3.1356 Volts
    3.1356V/1.7625 Ohms = 1.78 Amps

    Even with this real world results may differ.
    Inductive Reactance may add to the total resistance of the coil. (Not sure, still researching.)
    For your complex shape, I don't have a clue.
    Just sharing what I have learned so far.

    I hope this helps.
    Last edited: Sep 16, 2009
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