Inductor

Discussion in 'General Electronics Chat' started by James4553, Nov 26, 2008.

  1. James4553

    Thread Starter Active Member

    Jun 7, 2008
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    Hi Guys,

    I'm just wondering what an inductor is useful for?
    And what about the counter EMF?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Counter EMF only gets involved if there is another mechanism, such as in a motor. When you power up a motor it also becomes a generator simultaniously, which generates a nearly equal but opposite current, which resists the current you are feeding it. If you force a motor to stall the counter EMF goes away, and causes the motor to draw a lot more current (sometimes huge amounts).

    Inductors are exactly opposite of capacitors, their antiparticle if you will. They also store electricity, as current. You stop current flow and the inductor tries to keep it flowing by generating large voltage surges, much like a capacitor can generate huge current surges.
     
  3. James4553

    Thread Starter Active Member

    Jun 7, 2008
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    Bill; Sorry for being such a newbie but is it capacitors that store voltage and inductors that store current?

    Also, is it correct that inductor's impedence to the circuit is determined by the frequency of the signal?

    Also (sorry!), why would you use an inductor to oppose current instead of just using a resistor?
     
    Last edited: Nov 26, 2008
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    There is a piece written in the AAC eBook.
    http://www.allaboutcircuits.com/vol_1/chpt_15/index.html

    More links on the subject Coils and inductors can be found in the EDUCYPEDIA.
    http://www.educypedia.be/electronics/coilsrelay.htm

    There are more pages on other subjects over there too.

    Passive semiconductors technology: Batteries Diodes Photovoltaic systems Switches Buzzers Diode types Quartz crystals Thermoelectric Capacitors General overview Relays Transformers Capacitor types Heat Sinks Resistors Transformers-RF Coils Photo diode Resistors-Nonlinear Transformer types

    Greetings,
    Bertus
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Inductors and Capacitors both store energy. It's their relationship to voltage and current that are opposite.

    V = L*dI/dt
    I = C*dV/dt

    Energy

    Inductor: 0.5*L*I^2
    Capacitor: 0.5*C*V^2

    Steve
     
  6. Ratch

    New Member

    Mar 20, 2007
    1,068
    3
    James4553,

    1) As a dynamic energy storage device.
    2) As part of a resonant circuit.
    3) As an AC current limiter.
    4) As an AC current/voltage phase shifter.

    Counter voltage is always present when the coil current is changing. During that time it is storing or releasing energy in a magnetic field. The value of the counter voltage is directly proportional to the rate of current change. During the time that no current change is present, the coil sustains a steady magnetic field where energy is stored. This field always present when current exists.

    No, both store energy. Capacitors store energy in a electric field, and inductors store energy in a magnetic field. Voltage and current by themselves are not energy. Voltage sustains a electric field, and current sustains a magnetic field.

    Yes, inductive impedance is proportional to the frequency and also to the value of the inductance.

    Inductors only oppose current in AC and transient circuits. Inductors and resistors oppose current by two different mechanisms. Inductors generate a back voltage which opposes current changes. During that time, energy is stored during one-half cycle and released during the next half-cycle. No energy is expended. Resistors reduce voltage by dissipating energy. Since voltage is the energy density of the charge, pushing a charge through a resistor will reduce the amount of energy the charges contain, and thereby the energy density of the charge. So the voltage will decrease because the energy is reduced and dissipated as heat. Of course this works with resistors for DC too. In summary, inductors and capacitors reduce current by back-voltage, and resistors reduce current by dissipating energy.

    Ratch
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    A common application for this is florescent ballasts. A resistor generates heat (sometimes lots of heat) resisting current flow. This is pure waste. A coil does it differently, no heat involved, which is why florescent bulbs are generally so efficient.

    WWII subs used florescent bulbs in subs, but had DC power, so they were stuck with the resistors. The bolted the resistors to the nearest bulkhead to dissipate the heat.

    TMI? :D
     
  8. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Now you know.
     
  9. James4553

    Thread Starter Active Member

    Jun 7, 2008
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    So the inductive impedance is proportional to the frequency and the value of the inductor, but what about the magnitude of the signal? I would think a larger signal would mean more impedance since the change of current in the postive and negative cycles of an AC signal would be greater. Or does the magnitude not make a difference, only the frequency and value of the inductor?

    And (last question), is inductive reactance just another name for the resistance a inductor provides to the circuit?
     
  10. Ratch

    New Member

    Mar 20, 2007
    1,068
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    James4553,

    Only the frequency and value of the inductor. You should be able to discern that easily by examinining the formula for inductive reactance.

    No, inductive reactance is part of the impedance of the coil. The resistance of the coil from its wire is usually minimal compared to the inductive reactance. Read up on impedance and reactance relate to each other, and review what I posted before in this thread.

    Ratch
     
  11. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Or maybe you should familiarize yourself with what a differential equation means. I gave you the information above, which is pretty much all the theory you need to analyze a circuit with an inductor.
     
  12. James4553

    Thread Starter Active Member

    Jun 7, 2008
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    0
    Thanks guys for all the help
     
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