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Thread: Inductance In Circuits

  1. #1 Inductance In Circuits 
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    A newbie question for you here. I'm reading a guide on basic electronics, and I'm stuck on the section for inductors. I understand what an inductor is, a coiled wire that concentrates a magnetic field, but what is the purpose of it? What does the magnetic field do for the circuit? I read Wikipedia's page on inductance and didn't see such an explanation; I did, however, see some enigmatic equations that will haunt my dreams for years.


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    Of course, I find a separate article for 'Inductor' and feel like a fool. So an inductor maintains DC current... does the magnetic field created by the coil have adverse effects on other parts of the circuit?


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    Quote Originally Posted by Frenchi
    Of course, I find a separate article for 'Inductor' and feel like a fool. So an inductor maintains DC current... does the magnetic field created by the coil have adverse effects on other parts of the circuit?
    Inductors are not often found as devices intentionally placed in a circuit. They have a few applications like in rectifier filters, for example. Inductance is introduced unintentionally by devices like electric motors, relay coils, and long lengths of wire, like transmission lines. Yes it does have undesirable effects.

    In electronic circuits it can create havoc, because when you open a switch, interrupting the current, the sudden change in current results in high voltage which can damage things like switch contacts or electronic devices.

    It is the enemy of electrical transmission because inductive loads like large motors cause a phase shift that requires higher current over the transmission line to deliver the same power. Higher currents translate into greater line loss. Sometimes power factor correction capacitors are installed near the inductive load to counteract this.
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    Thanks Harold
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    Quote Originally Posted by Frenchi
    Thanks Harold
    You're welcome. One other thing I should have mentioned. An inductor can be made in a toroid form which hardly has any leakage magnetic flux. That is what you would probably use if you have an electronic circuit that might be susceptible to the interference.
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    Quote Originally Posted by Harold14370
    Quote Originally Posted by Frenchi
    Thanks Harold
    You're welcome. One other thing I should have mentioned. An inductor can be made in a toroid form which hardly has any leakage magnetic flux. That is what you would probably use if you have an electronic circuit that might be susceptible to the interference.
    When you say toroid shape, do you mean like the wind of a variac?

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    William McCormick
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    Quote Originally Posted by William McCormick
    [
    When you say toroid shape, do you mean like the wind of a variac?
    Yes, a variac is in the shape of a toroid.

    A toroid has a magnetic core shaped like a doughnut.

    If you just took an iron bar and wrapped coils of wire around it, that would make an inductor. the magnetic flux lines would tend to follow the iron core because iron has less reluctance than air. But at the end of the iron bar, the flux lines have to loop back around through the air to complete the magnetic circuit.

    If you took that iron bar and bent it back around on itself, you would have a toroid. the magnetic flux lines could just go around in a circle staying within the iron core.
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  9. #8  
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    Inductors are also used in speaker crossovers to make sure low frequencies do not go to the tweeter (high frequency driver). The higher the frequency, the higher the inductance and the more the signal is attenuated.
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    Quote Originally Posted by Harold14370
    Quote Originally Posted by William McCormick
    [
    When you say toroid shape, do you mean like the wind of a variac?
    Yes, a variac is in the shape of a toroid.

    A toroid has a magnetic core shaped like a doughnut.

    If you just took an iron bar and wrapped coils of wire around it, that would make an inductor. the magnetic flux lines would tend to follow the iron core because iron has less reluctance than air. But at the end of the iron bar, the flux lines have to loop back around through the air to complete the magnetic circuit.

    If you took that iron bar and bent it back around on itself, you would have a toroid. the magnetic flux lines could just go around in a circle staying within the iron core.
    I did note an amazing lack of inductance from the variac. I have an old TIG welding machine. I love it, I believe it is from around 1938, because the other one I used to have was from 1943 with a manufacturing date stamped on it, and this one appears to be much older. It has a ceramic 110 volt utility receptacle, and the styling of the machine itself appears older. But the control systems are so simple and so basic, that it just never breaks down. This machine should be looked at for its simplicity. There are no chips or tubes in it to blow.

    But my point was that it has copper bridge rectifiers, heavy ribbon wound transformers, and the power is controlled by variac. This machine has not stopped working since it was built. It is a real work horse and makes some pretty TIG (Tungsten Inert Gas) welds. I believe it is the quietest nicest DC output I have ever come across. The safest machine in my opinion, that I have ever used.

    All the newer systems seem to have an audible buzz.

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    William McCormick
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    Quote Originally Posted by Cold Fusion
    Inductors are also used in speaker crossovers to make sure low frequencies do not go to the tweeter (high frequency driver). The higher the frequency, the higher the inductance and the more the signal is attenuated.
    I believe the short high frequency burst does not have the RMS to move the inductance field. Of say a woofer, and is probably unwanted at the woofer.

    And the bass signal is probably taken out of the high frequency with small capacitors, that limit a pulse to very high frequency pulses. The bass goes to the high frequency speakers or tweeters but only acts for a fraction of a second.

    Much like a radio tuner.

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    William McCormick
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