Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How many turns On the Coil

  1. Nov 12, 2012 #1
    Hello there

    Its a air core coil I am not too sure how to calculate the
    number of turns I have to wind.

    Specs are below

    Height : 4mm
    Outside D: 9.5mm
    Inside D :7mm
    Coil wire thickness : 40 AWG / 0.08mm
    Coil resistance : 55 Ohms
    Coil weight : 0.7g

    Important figures highlighted. I have made a detachable bobbin.U sing self bonding wire.
    coil is air -core.

    How can I calculate the number of turns that i would require to make this coil

    Thank you
    Edit/Delete Message
     
  2. jcsd
  3. Nov 12, 2012 #2
    Turns = turns per layer * number of layers

    turns per layer = height / wire thickness = 4 mm/0.08 mm = 50

    number of layers = (OD-ID)/(2*wire thickness) = (9.5-7)/(2*0.08 ) = 31.25 = 31 layers

    therefore, Turns = 31 * 50 = 1550
     
  4. Nov 12, 2012 #3
    oh btw that's assuming rectangular packing, if its triangular packing then divide the result by 0.78
     
  5. Nov 13, 2012 #4
    Having been in the transformer business, I'm very pessimistic.
    Phelphs dodge gives for #40 Bondeze wire a nominal diameter of 0.0037 inches.
    This works out to a diameter of 0.0939 mm.

    When hand winding you usually get maybe 60% fill.

    #40 wire is THIN, so is extremely difficult to work with.

    Good Luck
     
  6. Nov 13, 2012 #5
    Carl is right, AWG 40 breaks incredibly easily. 60% is also a more practical number, so multiply the result I originally gave you by 0.6 (or if using triangular packing, which I suspect is what it would come down to, divide by 0.78 then multiply by 0.6)
     
  7. Nov 14, 2012 #6
    You need 15.4m of wire to achieve the resistance. 0.08mm needs care.

    With a setup that rotates the coil former you can still make a perfectly compact coil of 0.08mm by hand but only with training and good hands.

    Then each layer packs nearly 50 turns, I estimate 47 (again under good conditions...) so the first layer packs 1.0m and the latest 1.4m with 1.2m as a mean, so you need 13 layers.

    I could never pack properly successive layers in the same direction (wire returns makes a mess), nor did I see a coil made this way, so each layer takes >0.08mm and the 13 perfect layers fit well in OD=9.5 ID=4

    BUT

    you'd go crazy before finishing the 13 layers. With said training and good hands you achieve 4 layers or 50 turns with this tiny wire, then you throw all through the window.

    Next solution: pack the wire disordered, taking advantage of the available 50% filling factor. For 650 turns of tiny diameter you DO need to rotate the coil former or you'll break the wire. At 50% filling you can't make much of a mess, the winding must already look good.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook