Testing an Inductor

Discussion in 'General Electronics Chat' started by EE_joe, Oct 17, 2005.

  1. EE_joe

    Thread Starter New Member

    Oct 17, 2005
    1
    0
    ok, I'm an EE intern at a Mechanical Engineering firm, and need help.
    I've been assigned to test a circuit... simple enough

    well, it's been awhile since i've done circuit stuff. more of a communications guy myself (and not the circuits side).

    here goes:

    I wound this inductor (has power applications), with a tested value of 155 H.

    I'm supposed to hook this thing up to make sure it behaves the way it would in it's soon to be operating environment.

    I'm testing with a frequency of 1kHz, the real EE said I should choose a resistor such that there is about a 50V drop and a 3A drawn. Also, I'm supposed to vary the DC current to see how the inductor reacts.

    1) What resistance should I use?
    2) What is the expected behavior of the inductor as I vary the DC current?

    Now, don't make too much fun of me please.... I already get enough of that. Thanks, any help is appreciated.
     
  2. Overclocked2300

    Senior Member

    Apr 24, 2005
    124
    0
    Well if your resistor needs to be drop 50@3Amps then,

    R=V/I

    Where
    V=Voltage
    I= Current

    So

    50/3

    r=16.6666667 Ohms.

    An inductor resists any changes in current. Think about what happens when you give it the 1Khz Signal.
     
  3. mentaaal

    Senior Member

    Oct 17, 2005
    451
    0

    hey hows it going.
    em... i am a newbie myself and am interested in electronics but only just getting just getting over the fundamentals at this point.

    Here goes:
    I think the reactance for such an inductor (assuming no internal resistance) at 1000 hertz would be: 2pieFL = 973893.72 Ω

    the value of the resistor you need depends entitrely on the input voltage which you have not supplied.

    All you have to do is get the value for voltage and then use V=RI (with the condition that R is a value for impedance and is expressed in polar form)

    Then stick 3 amps in for I and solve for the required impedance. you can base your required resistor on this.

    I hope this helps and I hope to God its right.
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6

    That's a darn huge inductor. Is it possible that the tested value is 155mH or 155uH instead of 155H?

    <!--QuoteBegin-EE_joe
    @Oct 17 2005, 01:45 PM
    2) What is the expected behavior of the inductor as I vary the DC current?
    [post=11056]Quoted post[/post]​
    [/quote]

    For a 155mH or 155uH, one probably won't see any behavior with changing DC current. (Unless one has very expensive test equipment.) You will, however see change as you vary the AC frequency.

    If it truly is a 155H coil, then you will indeed be able to watch it oppose the change in DC current.
     
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,158
    You could use an Excel or any spreadsheet to see what you can expect.

    Anything past DC you can expect the voltage to decrease across the resistor and the voltage to increase across the Inductor.

    I put a 15 ohm resistor in series with the 155 H inductor. A 50 volt source gave me a little over 3 amps in the DC circuit.

    Anyways, here's a plot of the voltage across the Inductor and the Resistor from 0 to 1 Hz.
     
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