Question on measuring inductor coils

Discussion in 'General Electronics Chat' started by keithostertag, Mar 12, 2014.

  1. keithostertag

    Thread Starter Member

    Oct 4, 2012
    48
    2
    I found this set of vintage Phywe inductors at a yard sale and thought they might be fun to play with.

    [​IMG]


    They are marked 300 (4A), 600 (2A), 1200 (1A), and 12000 (0.05A).

    I assume the "A" figures are current ratings, but I can't figure the other numbers.

    All these are approx the same size and shape, 1.25" diameter coil form about 2.5" long.

    Using this webpage to estimate the inductance:

    http://www.dos4ever.com/inductor/inductor.html

    And the values don't come close to the coil markings. Here are the figures I measure:

    300 (4A) coil- 2.3mH (2300uH), DC resistance = 0.65 ohms
    600 (2A) coil- 8.9mH (8891uH), DC resistance = 2.3 ohms
    1200 (1A) coil- 30mH (30,000uH), DC resistance = 11.5 ohms
    12000 (0.05A) can't measure, DC resistance = 1430 ohms

    Working backwards using formulas, speculating the markings might refer to the number of windings, the figures I get don't correspond.

    So what is your guess to what the markings are referring to? Am I simply using the wrong method of estimating?

    I wonder if the square openings were designed to insert iron or other core materials?

    Thanks,
    Keith Ostertag
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    They were typically used in lab experiments and teaching as you already may have guessed, but there is usually a soft iron laminated bar that goes with them.
    Max.
     
  3. keithostertag

    Thread Starter Member

    Oct 4, 2012
    48
    2
    Hi Max- thanks. Yea, I assumed they were lab experiments and wondered about a required bar...

    Do you guess an inserted iron bar would raise the inductance from, say, 2.3mH to 300mH in the case of the small one? Just trying to figure out what the markings refer to.

    Thanks,
    keith
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    They are about as old as I am, but they probably have more 'memory' ;)
    Max.
     
  5. activex

    New Member

    Mar 5, 2014
    3
    0
    i think the other number is number of turns and the other is amp as you mention. this may look like a transformer, too, so, more turn means higher voltage but less current.
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,364
    They are used in physics labs for demonstrating the operation of transformers.

    Pasco sells these:

    [​IMG]
     
    keithostertag and #12 like this.
  7. crutschow

    Expert

    Mar 14, 2008
    13,042
    3,243
    I also think the larger number is the number of turns. Thus when two are used as a transformer with a common core you can see how the relationship of the number of turns between the primary and secondary compares to the voltage ratio.
     
  8. keithostertag

    Thread Starter Member

    Oct 4, 2012
    48
    2
    Thank you gentlemen! Very useful info, particularly the PASCO link.

    Keith
     
Loading...