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

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35 Responses to “How to make an Air-Core Inductor”

  • oracle says:

    sir, i would want you to tell me the number of turns for making 0.01uH. thanks

  • nishant says:

    will you please tell me how to calculate gauge of wire in this?

    • Seetharaman says:

      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.

  • Shailendra says:

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

  • sagar says:

    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

    • Seetharaman says:

      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.

  • ashika says:

    sir i want to make a 0.1microhenry indutor coil so what will be the values of d n and l

  • Rex says:

    Seetharaman, is there any difference between 10uH and 10mH or are they thesame?

  • zeeshan says:

    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

  • shaka myeni says:

    nice one!

  • Chinthaka says:

    Hai Dear Sir,

    1 need 1mH 1amp inductor and 4mH 1Amp inductor please kindly tell me how can i do this.

  • sadiq ali says:

    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.

  • khurshed says:

    sir,
    if i want to make a 53uH coil by 24Awg,the arc is 15cm.then what will be the number of turn?

  • ashnuka says:

    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.

  • Hemant says:

    nice post thanks!!
    But L=MicroHenries

    So in your example is must be a typo “L=10 inches” it should be 10 uH

  • Seetharaman says:

    Hi Shinoj AWG is american standard for wires. SWG is standard wire gauge for British and Europien standards. There will be a difference between both the standards. there are conversion tables available to compare both standards. a sample is shown below
    http://www.qsl.net/lx2sm/conversion1.htm

    • Victor Ak. says:

      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.

  • Shinoj says:

    What is mean by AWG and SWG

  • seetharaman says:

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

  • Anish says:

    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.

  • Anish says:

    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.

  • seetharaman says:

    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.

  • Anish says:

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

  • master i try your formula but i have no luck. how do i produce .01uf

  • Abhishek says:

    How to use it as Centre tapped Inductor , for connections to Antenna?? in A radio receiver.

  • Jady Burg says:

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

  • Acme Fixer says:

    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

  • Seetharaman says:

    Hi Jatin 1mH(milli henry) is 1000micro henries substute in the above formula.

  • Jatin says:

    How to make an inductor of 1mh

  • Seetharaman says:

    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.

  • fady says:

    How to make a RF choke 200 to 500 uf

  • ahtasham says:

    how to conect the headphone socket in the circuit as it has 3 plugs
    plz ans me as soon as possible