How to make an Air-Core Inductor

Sometimes you may be unable to find a particular inductor the market. This is actually a problem faced by most of the electronic hobbyists and the problem becomes more serious if your project is RF related. The inductors required for RF circuits (antenna, tuner, amplifier etc) are almost impossible to find in the market and the only solution is nothing other than home-brewing them.

how to make an air cored inductor

With a little practice and patience you can construct almost all air cored inductors at home. The inductance of an air cored inductor can be represented using the simplified formula shown below and to calculate the inductance of an air-core inductor, the same equation may be used.

L  = [d2 n2] / [18d + 40l]

  • Where’ L ‘  is the inductance in Micro Henries [µH]
  • ‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches.
  • ‘l’ is the length of the coil specified in inches.
  • ‘n’ is the number of turns.

Notes :

  • The length of the coil used in the inductor should be equal to or 0.4 times the diameter of the coil.
  • As shown in the equation, inductance of the air-core inductor varies as the square of the number of turns.  Thus the value ‘l’ is multiplied four times if the value of ‘n’ is doubled.  The value of  ‘l’ is multiplied by two if the value of ‘n’ is increased up to 40%.

Winding the coil.

  • The coil must be first wounded on a plastic former of the adequate diameter (equal to the required core diameter).
  • The winding must be tight and adjacent turns must be as close as possible.
  • After the winding is complete, slowly withdraw the core without disturbing the coil.
  • Now apply a thin layer of epoxy over the coil surface for mechanical support.
  • Remove the insulation from the coil ends.

Example

Suppose you want to make an inductor which produces an inductance of 10 μH. The diameter of the coil is 1 inch and the coil length is given by 1.25 inches. You will have to find the number of turns of the coil.

Thus substituting the values in the above equation t

L = 10 inches

d = 1inch

l = 1.25 inches

n = √{L [18d * 40l]} / d = 26

Thus, the number of turns of the coil will be 26.

Number of turns/inch = 20.8

Show Comments

41 thoughts on “How to make an Air-Core Inductor

    • Seetharaman

      The gauge depends on the current flow required to flow through it. for RF application it should be at least 18 SWG or thicker as the signal current flows through the surface of the wire. hence to increase the conducting area use a thicker wire.

      Reply
  1. Shailendra

    Sir I want to make a coil of 150uH. So what should be the values according to this.Please tell me.

    Reply
  2. sagar

    sir i make 6Mh inductor
    with 272 turns,
    22 Gauge copper wire
    2inch(50.8mm) diameter OD
    with PVc material as forme.
    now i want to calculate the value of l,N, d
    can you please tell me how to find these values

    Reply
    • Seetharaman

      use the formula
      L = [d2 n2] / [18d + 40l]
      Where’ L ‘ is the inductance in Micro Henries [µH]
      ‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches.
      ‘l’ is the length of the coil specified in inches.
      ‘n’ is the number of turns.

      Reply
  3. zeeshan

    sir i have to filtering the 50vdc please tell me how much inductance are required to filter 50v dc and what is the length ,no of turns and insulator width and wire gauge

    Reply
  4. sadiq ali

    I AM MAKING MOBIEL JAMMER NOW A DAY,s I REQUIER 22 MILE HENRY INDUCTER COIL
    WICH 500 MHZ USE IN CIRCUIT I DONT KNOW ABOUT IT I WANT TO MAKE IT PLEASE HELP OR SUGESTION ME.

    Reply
  5. ashnuka

    I want a 0.156uH(Micro Henries) inductor and i use 18swg wire.Can you please tell me what would be the values of d,l and n.

    Reply
    • Victor Ak.

      Hello Sir, am very greatful on your contribution to educate the electronics curious people which am also the beneficiary of ur programme, please kindly publish a wireless transmission signal circuit for speakers to sound transmitting system.

      Reply
  6. seetharaman

    Hi Anish you have contact a motor/transformer winder or a good electric supplier who will be in a position to supply.

    Reply
  7. Anish

    Thankyou sir,
    But where do I get these wires. Like tell me some local shops where I can buy these wires. And how to ask them. Once I asked for a 24AWG copper wire in a radio house where i buy electronic components.. They are blinking.

    Reply
  8. Anish

    Thankyou sir, but where do I get these wires. Like tell me some local shops where I can buy these wires. And how to ask them. Once I asked for a 24AWG enamelled copper wire in a radio house where i buy electronic components.. They are blinking and saying they never heared such thing.

    Reply
  9. seetharaman

    Hi Anish it depends on the application. For higher current a thicker (lower gauge number say 18 or 16SWG) of wire is required. For lower current thinner (higher gauge number say 32 or 38SWG) wire will do. For low frequency coils say Medium Wave a litz wire is preferred. For higher frequencies say at 200MHz or greater thicker wire is preferred, not that it has to flow higher current but higher frequency current flows through the skin of the wire. You refer to gauge table you can find the details.

    Reply
  10. Anish

    Hi sir,
    What type of coil wire to use? 22SWG, 24SWG etc,,, they recommend different type for different applications. How to find that?

    Reply
  11. Jady Burg

    great joob really help fulll but insulater is must for winding or any other material can be used
    ??????????????????????

    Reply
  12. Acme Fixer

    Someone asked how to make a 200 to 500 uH coil. These were the parts values given for the L3 in the 2 km FM transmitter. This choke is not needed for this project. I explain why in my blog here.

    watsonseblog.blogspot.com/2011/01/2011-jan-25-circuitstoday-fm-tx.html

    Reply
  13. Seetharaman

    Hi Fady you mean 200 to 500uH (micro henrys) use tha above formula. it cannot be variable but either 200 or 500uH can be made.

    L = [d2 n2] / [18d + 40l]

    •Where’ L ‘ is the inductance in Micro Henries [µH]
    •‘d’ is the diameter of the coil from one wire centre to another wire centre. It should be specifies in inches.
    •‘l’ is the length of the coil specified in inches.
    •‘n’ is the number of turns.

    Reply
    • abhijith sivan

      sir. i am new to this feild but i am very interested in this. would u plz tell me how many turns required for 22nh at which size wire??

      Reply

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