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Thread: Question on AC currents

  1. #1 Question on AC currents 
    Time Lord
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    What happens if two AC currents of the same frequency, but exactly a half wavelength out of phase with each other, flow through two wires of equal length, which then connect to the same lightning rod?


    Will they just cancel each other out and disappear? Or do they get reflected back toward their source (away from ground)?


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  3. #2 Re: Question on AC currents 
    Forum Professor Wild Cobra's Avatar
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    Quote Originally Posted by kojax
    What happens if two AC currents of the same frequency, but exactly a half wavelength out of phase with each other, flow through two wires of equal length, which then connect to the same lightning rod?


    Will they just cancel each other out and disappear? Or do they get reflected back toward their source (away from ground)?
    Well, frequency and distance can be a factor. However, if you are talking about common AC over a short distance, you just tripped your circuit breaker.


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  4. #3  
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    Suppose you had a battery with voltage V connected in a circuit of resistance R. A current of I=V/R would flow. Now get another battery and connect it in series with the first battery but opposite polarity. It causes a current of -I to flow in the circuit, and by superposition, the sum of the two currents is 0.

    The same thing happens if you connect two transformers in series 180 degrees out of phase, i.e., nothing.
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  5. #4  
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    Quote Originally Posted by Harold14370
    Suppose you had a battery with voltage V connected in a circuit of resistance R. A current of I=V/R would flow. Now get another battery and connect it in series with the first battery but opposite polarity. It causes a current of -I to flow in the circuit, and by superposition, the sum of the two currents is 0.

    The same thing happens if you connect two transformers in series 180 degrees out of phase, i.e., nothing.
    Huh?

    Are we visualizing this different?

    180 degrees is opposite polarity, and would allow maximum current between the two sources of power. 0 degrees would be in phase and have no current between the two. There will only be power radiated is there is an effective antenna.
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  6. #5  
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    Quote Originally Posted by Wild Cobra
    Are we visualizing this different?

    180 degrees is opposite polarity, and would allow maximum current between the two sources of power. 0 degrees would be in phase and have no current between the two. There will only be power radiated is there is an effective antenna.
    I was visualizing two voltage sources of opposite polarity connected in series, with the load also in series. You are visualizing two sources of opposite polarity connected in parallel, then to the load.

    Now that I reread the question, yours is probably closer to the original question.

    There is a node where the wires connect to the antenna. The sum of currents in a node must be equal to zero, so if you have +I from one source and -I from the other source, the result is zero to the antenna.
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  7. #6  
    Forum Professor Wild Cobra's Avatar
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    Quote Originally Posted by Harold14370
    Quote Originally Posted by Wild Cobra
    Are we visualizing this different?

    180 degrees is opposite polarity, and would allow maximum current between the two sources of power. 0 degrees would be in phase and have no current between the two. There will only be power radiated is there is an effective antenna.
    I was visualizing two voltage sources of opposite polarity connected in series, with the load also in series. You are visualizing two sources of opposite polarity connected in parallel, then to the load.

    Now that I reread the question, yours is probably closer to the original question.

    There is a node where the wires connect to the antenna. The sum of currents in a node must be equal to zero, so if you have +I from one source and -I from the other source, the result is zero to the antenna.
    Yep, I thought we read it differently.
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  8. #7  
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    PLEASE DO NOT DO THAT. TAKE UP A COMPLETELY DIFFERENT HOBBY.
    "Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense." --Buddha (563BC-483BC)
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  9. #8  
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    I think he's saying he wants to take 2 , 120v mains opposite phased and run them through a wire, so a 240V source, bottom line is if the wire is a certain length, and the load is proper size it will hold a certain impedance to cancel out the signal,

    IF your load is 1K ohm you need your wires to be about 300 heneries on EACH wire (use an induction calc to measure your wire, it adds up to ALOT of wire though)
    you will wind up with 1V on the load and 1/1000 amps of current

    A lightning rod prolly only has 10ohms resistance though so you need 3 heneries on Each wire and that will leave you with 1Volt again but 1/10Amps or 100mA

    still alot of wire though!!!
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