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.
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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nice post thanks!!
But L=MicroHenries
So in your example is must be a typo “L=10 inches” it should be 10 uH
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
What is mean by AWG and SWG
Hi Anish you have contact a motor/transformer winder or a good electric supplier who will be in a position to supply.
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.
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.
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.
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
How to use it as Centre tapped Inductor , for connections to Antenna?? in A radio receiver.
great joob really help fulll but insulater is must for winding or any other material can be used
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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
Hi Jatin 1mH(milli henry) is 1000micro henries substute in the above formula.
How to make an inductor of 1mh
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.
How to make a RF choke 200 to 500 uf
how to conect the headphone socket in the circuit as it has 3 plugs
plz ans me as soon as possible