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specifying inductor wire

Discussion in 'Electronic Design' started by Michael, Jun 12, 2008.

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  1. Michael

    Michael Guest

    I have 1.25" OD toroid for which I need to specify wire.
    Inductor specs:
    The wire is 24AWG (thin)
    There are only 19 turns - they are separated on the core.
    The leads are ~2"long and tightly twisted (4-5 twists per inch).
    The inductor sees 200V applied across it's terminals.
    Operating temperature will never exceed 50-60 degrees C.

    Magnet wire comes to mind, right?
    My concerns are:
    if enamel is damaged/nicked, twisted leads may short (with
    catastrophic consequences)
    If/when manufacturing is sent out to China, God knows what kind of
    insulation will be used there (we are having problems with Chinese CM
    quality)

    Here is my question to all the experts:
    What is cheaper/easier to manufacture
    generic magnet wire with both leads in some flexible tubing (I want
    leads to be tightly twisted) OR
    make everything out of UL1007 (or equivalent) solid hookup wire

    I cannot get a straight answer from our (local assembly house). They
    say that magnet wire is cheaper (how much do I save on 19 turns @<5000
    units per year???); magnet wire can be purchased with heavy insulation
    (how to specify it??); Teflon/shrink tubing is commonly used (is it
    cheaper??).

    Thank you in advance for your help and sorry for the long posting.
     
  2. Eeyore

    Eeyore Guest

    Why ?

    Use thicker magnet wire if you can. I haven't a clue what 24 AWG is but
    0.3 - 0.4 mm isn't too fragile.

    I have been known to use PVC insulated wire on toroids when I was
    concerned about abrasion.

    Graham
     
  3. Tom Bruhns

    Tom Bruhns Guest

    Why not contact a magnet wire supplier and ask them? My experience is
    that they have a lot of experience in this area and will be happy to
    help you out. A Google search will turn up several. New England Wire
    (http://www.newenglandwire.com/) is one I happen to like, but there
    are several other good ones.

    You didn't say much about the inductor, but 200V across 19 turns on
    that physical size core suggests to me that either it's a very high
    permeability core, or the frequency is high, or some of both. Would
    the application benefit from higher Q? 24AWG is quite small for 19
    turns on that size core; I suppose you could use 14AWG on it, or get
    about 100 turns of 24AWG in a single layer on it. And you may benefit
    from using Litz wire, too. Is the core size chosen for core loss or
    for saturation? You may be able to save far more by using a core
    better suited for the application, than by worrying about what type of
    wire to use for a 30 inch length of 24AWG, almost independent of the
    insulation you put on it -- again suggested by the very small wire
    you're using on that core. If you _really_do_ only want to use 24AWG
    solid wire on such a large core, for your concerns, I'd say to just
    use PVC-insulated hookup wire. But it doesn't sound like a very
    optimized design to me, from the little I know about it.

    "mini Ring Core Calculator" available free on the web may be
    interesting to you.

    Cheers,
    Tom
     
  4. legg

    legg Guest

    Depending on the core coating, there is little liklihood of shorting
    through the core body, without extreme external abuse, post-assembly.
    Pre-specifying alternate core types from alternate vendors can reduce
    part cost and delivery time.

    Specify easily-obtained and alternative magnet wire grades in your
    intended insulation temperature class range. Popular 130degree
    solderable types are MW28/MW75 or MW79/MW80. Do not specify a vendor
    or trademarked material.

    You might want to give some consideration to mounting and termination
    methods.

    For wave solderable assemblies, platforms can be used, with the part
    body epoxied into position and the leadout wires rigidly located.
    Identification labelling should be present and permanent. Pre-formed
    platforma are available from Lodestone, Cosmo and many core
    manufacturers.

    For parts with longer flying leads, you should consider stranded
    insulated lead wires. In a part like this - you might just as well use
    stranded leadwire for the complete winding.

    A really simple part is likely to have off-the-shelf alternatives.

    RL
     
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