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Inductor with a Magnet

Discussion in 'Misc Electronics' started by Watson A.Name - Watt Sun, Dark Remover, Nov 10, 2003.

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  1. I pulled some ferrite core chokes out of a Compaq monitor and one had
    a magnet on the top, held on by heat shrink tubing. I measured the
    inductance with the magnet on, and it measured 8.2 uH. I cut off the
    HST and removed the magnet, and the inductance shot up to 35 uH. I
    think this has something to do with varying the permeability.

    I don't remember seeing anything about this kind of choke in any
    electronics manuals, so I thought I'd do a web search but I came up
    with nothing. I tried magnetically polarized inductor and magnetic
    core inductor, but neither gave any info that I could find. Do you
    know what they call these devices? Thank you.


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  2. Try magnetically biased. Placing the magnet on the inductor really is
    shifting the saturation point so that in one direction of current flow, it will
    saturate easily but in the other, it will not.

    Cheers!

    Chip Shults
    My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
     
  3. John Todd

    John Todd Guest

    Wow! A new 'field' of interest!
    Using "flux biased inductor" gave one link to
    a NASA paper, using a magnet in the air gap.
    Sorry, the tiny browser I used doesn't have cut/paste (dillo).
     
  4. I didn't see that when I googled on flux biased inductor, but I did
    see a bunch of weird stuff like SQUIDs, Josephson junctions, and even
    a flux capacitor(!)

    You should be able to highlight the text, do a Ctrl-C for copy, and
    then in the other prog, do a Ctrl-V for paste.

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    Just when you thought you had all this figured out, the gov't
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  5. Graham W

    Graham W Guest

    It is a horizontal linearity control.
     
  6. Dave VanHorn

    Dave VanHorn Guest

    These are used where you are going to have a really large DC current, like
    in a horizontal sweep section, or boost converter. The magnet biases the
    core "negative", allowing the current to use the full area from "negative"
    to "positive" instead of just from zero to "positive".

    You could just use a larger core, but then the inductance goes up, material
    gets expensive etc.
     
  7. I've been using toroids and pot core inductors for the LED V boost
    converters I've been making. Looks like I can't put a magnet on
    those.

    So I took the magnet off, and the inductance went up from 8.2 uHy to
    35 uHy. It would stand to reason that if I put enough current thru
    the coil to balance out the magnet's field, then the inductance would
    also be 35 uHy. There's no way I can do that, because the LC meter
    doesn't allow DC, to my knowledge. So I can't test out my theory.


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    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  8. Jeff

    Jeff Guest

    Also good for some signal shaping - when current goes one way it's at full
    inductance, when it goes the other way it has almost no inductance.
     
  9. Which one would it be measuring, then? :-[
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    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
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  10. Dave VanHorn

    Dave VanHorn Guest

    Toroids are out, and pot cores would be difficult.
    For this, you need a rod core.
    At least if you don't want to get into machining neodymium magnets.
    It can be done, find yourself a lapidary, with experience working opals.
     
  11. Dave VanHorn

    Dave VanHorn Guest

    That could work..
    Needs to be DC though, not varying DC like the input to the converter ckt.
     
  12. Dave VanHorn

    Dave VanHorn Guest

    the inductance does vary with current density.
    push the current too far, and the inductance pretty much goes away
    (saturation)
     
  13. I took some old .5 GB HDs apart at work and used the neodymium magnets
    to hold some pics to the file cabinet. Well, someone came over and
    took one off, and let it snap into the steel so hard that it broke
    into fragments, and the guilty party slinked off, never to admit his
    bad behavior. So there are some fragments holding one corner up, and
    it looks like the magnet is made of sintered particles, similar to
    ferrite. I'd say it's probably very difficult to machine this
    material, it'll just fracture if it's stressed.

    I'm taking a huge 5.25" full-height 8-platter Priam HD apart. It has
    a true linear motor for the heads, uses four BUZ71s to drive it in H-
    bridge, I believe. Really quite a mechanical marvel, but it holds only
    150 MB. Probably cost a couple thou back in early 1988, which is the
    date code on many of the chips.


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    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  14. Dave VanHorn

    Dave VanHorn Guest

    I took some old .5 GB HDs apart at work and used the neodymium magnets
    Like most rocks.
    Lapidaries are skilled in cutting and shaping rocks.
    The reason that I suggest someone with experience in opals, is that they are
    similar to Neodymium magnets, they die if they get too warm. Best cut in a
    stream of water.
    I've had NIB magnets machined this way, to exact sizes, while I was waiting
    on prototypes.
    The machined pieces had almost exactly the strength of the protos, when they
    finally arrived.
    At least as good a match, as I would normally get between batches.

    In the normal method, the magnet material is cut before charging, then they
    are loaded in the zapper, and charged all together, so if the material is
    decent, you'll get about 5% variation in a lot.
     
  15. Guest

    Try saturable core reactor. It's an old technique that relies on the
    fact that any magnetic core will have a value of flux that saturate
    and at that point the inductance will be far lower due the diminished
    influence of the core.

    I did some work about 35 years ago before veractors were common and
    cheap using a powered iron cored inductor that had a secondary winding
    to push DC through. Gave better tuning range than simple LC tuning
    with practical parts.

    More recently it was QEX or QST (brain fade) had a design for a loop
    antenna using a saturable core to vary the loading inductor for remote
    tuning.

    Allison
     
  16. DarkMatter

    DarkMatter Guest


    There ya go. Nearly all CRT type monitors have one.
     
  17. DarkMatter

    DarkMatter Guest


    One thing would be a cut off wheel on a Dremel tool. It would
    abrade the surface as opposed to trying to cut at it. Just like
    ferrites, not machinable.

    There are hard drive grave yards out there where working drives can
    be bought for a few bucks each.

    I have an old full height 5.25" ESDI drive that I took apart. The
    head mech is a huge linear motor, several head pairs. Absolutely no
    slew at all. Straight passes! Huge rare earth magnets, and big
    copper bars. Good inch and a half stroke.

    One of the most interesting little motors I've ever seen. As soon
    as I find it, I'll post some photos in alt.binaries.misc.
     
  18. But it doesn't have any adjustment.



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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
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  19. Graham W

    Graham W Guest

    The core in the coil may screw up and down OR the magnet may in a
    rotatable clip (unlikely in your item) OR there may be another coil in
    series with this one. Review the horizontal deflection circuits of as
    many TVs and monitors as you can find and you will see it is a very
    common component.
     
  20. Mark Jones

    Mark Jones Guest

    In news:6wasb.7090$9.net (Graham W):

    A customer called in today, storms went through her area and both her TV
    and monitor are hosed. The TV's image is "pinched," and the monitor's image
    is "skewed" and "all color-banded like the old TV's were."

    What do you think... electrical damage, or EMI magnetization?

    ;)
     
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