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Looking for formula to calculate gapped inductor

Discussion in 'Electronic Design' started by [email protected], Aug 15, 2007.

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  1. Guest

    Could anyone give me the formula for calculating the value of gapped
    inductor? I don't want to mess with theory, all I need is the equation
    and preferably in SI units. Thanks for helping ^_^
  2. Fred Bartoli

    Fred Bartoli Guest

    Le Wed, 15 Aug 2007 05:09:36 -0700, w2kwong a écrit:

    Could you give me the money your customer is paying you.
    I don't want to mess with marketing and such, all I need is the bank
    transfer, and preferably in Euros. Thanks for paying ^_^
  3. MooseFET

    MooseFET Guest

    I can't give you SI units but you can convert. A gapped inductor is
    worth about:

    Y = 43.2 + 1.7*G + 53*W

    Y = How much it is in US dollars
    G = The number of faces that you need to grind
    W = The weight in pounds

    I hope this helps.
  4. Tolstoy

    Tolstoy Guest

  5. D from BC

    D from BC Guest

    I take paypal :)

    D from BC
  6. What the hell is a gapped inductor?

  7. Joel Kolstad

    Joel Kolstad Guest

    You really should "mess with theory" at some point...

    But in the interest of answering your question... it's easy to compute the
    inductance of a gapped core vs. an ungapped core; the result is:

    L_gapped/L_ungapped = L_e/mu_r / (L_e/mu_r + L_gap)

    ....where L_e is the effective length that the flux traverses, mu_r is the
    relative permeability of the of the core, and L_gap is the length of the gap.
    L_gap, of course, has to have the same units as L_e.

    Notice that for large values of mu_r, the gap length alone starts to dictate
    the entire inductance.

  8. Bob Myers

    Bob Myers Guest

    Ummm...for instance, an inductor made on a
    toroidal or similar "closed" core shape, but with a
    slot cut through the core material. Think of a
    tape-recording head.

    Bob M.
  9. Iiiim, sorry. I call those gapped core. I thought he was winding an
    inductor with spaces between the windings.

  10. Bob Myers

    Bob Myers Guest

    Yeah, "gapped core" would be more common, but I'm
    pretty sure that's what the OP meant.

    Bob M.
  11. Guest

    Mates may I apologies for my poor expression, since English is not my
    first language. Tolstoy your link has been useful, thanks
    I'm still a UG student and don't get money for doing my thesis
    project. Instead I myself 'm paying thousand bucks to buy my own
    equipments, blown chips etc, and it's unlikely that I will be able to
    claim these cost from supervisor.

  12. You're an idiot. Almost ALL core manufacturers provide gapped cores
    per customer spec.

    I hope you get help.

  13. You have to actually possess the capacity to provide the required
    services before you would deserve a dime...

    Unless, of course, you are a doctor... Then you can shuffle folks in
    and out of your office all day, taking only vital signs, and billing
    insurance companies out the ass for near zero actual performed services.
  14. MooseFET

    MooseFET Guest

    I already knew that this was your latest nym. You didn't have to
    prove it with yet another example of your stupidity, but here we have
    such a fine example that I feel I should respond and fully quote what
    I said and how you responded so that others may enjoy a good laugh at
    your expense. Even those who have kill filed you, I am sure, will
    have a good giggle. You really didn't get it did you?
  15. MooseFET

    MooseFET Guest

    Beware that at large sizes of gaps, this equation is inaccurate. It
    assumes that the lines of force pass as straight lines from one face
    to another.

  16. "Large" is a fairly ambiguous choice of terms here.
  17. Joel Kolstad

    Joel Kolstad Guest

    Yes, good point. Another one I forgot to mention is that with cores that have
    mating surfaces (e.g., pot cores) the tiny spaces between the two touching
    halves can be enough such that there's sometimes already a non-negligible gap
    that makes the mu_r listed on the data sheet more of an "effective" value
    rather than the true bulk material value. This of course causes the equation
    listed to be somewhat inaccurate as well.

    Hopefully this guy measures the inductance he ends up with prior to using the
    device in a circuit...
  18. Traver

    Traver Guest

    Toroids actually have a "gap" as well but it is distributed though the
    core material without actually seeing a physical gap. With non -
    toriods like E-E cores for example, you need to gap the cores by
    putting a thin spacer in between the two Es or grinding down the
    center leg. This gives you the ability to chose the gap. Toriods come
    in a fixed gap with various discrete values.
  19. Terry Given

    Terry Given Guest

    if, and only if, its a distributed-gap core, e.g. iron powder, koolmu etc.

    for ferrite toroids, this statement is entirely incorrect.

    With non -
    conversely, this is only true for non-distributed-gap cores e.g.
    ferrite, metglass etc.

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