Introduction: Making a Simple Air Core Inductor (Induction Coil)

This instructable will tell you how to make a simple small air core inductor, specifically for Niftymitter. Niftymitter is an open source FM transmitter based on Tetsuo Kogawa's Simplest FM Transmitter,  a free running oscillator circuit, hence the need for a coil.

Step 1: What You Need

A small reel of enamelled copper wire.
A drill bit of the desired internal diameter of the coil.
Soldering kit and solder.
Wire snips and needle nosed pliers.

For Niftymitter, use 0.75mm (or 22SWG) diameter wire, such as this from Rapid and a 5mm drill bit.

SWG/metric conversions can be found on this page.

Step 2: Turning the Wire

Using the drill bit as a template, wrap the wire, counting up to the number of desired turns. Allow 3cm of wire clear before starting the turns and keep the wire taught while turning. Kogawa has a video for this step on his site here [.wmv].

For Niftymitter, make 4 complete turns, as close together as possible.

When complete, snip off from the reel at 3cm distance from the last turn.
 

Step 3: Forming the Legs

Use some needle nosed pliers to grip the coil on the bit as shown. Bend the legs as shown so that they are parallel. Remove from the drill bit.

Step 4: Tinning the Legs

The legs of the coil require tinning to remove the enamel and prime the surface for soldering onto a board.

Use some needle nosed pliers to grip the coil while tinning - it can get very hot. Heat one leg with the soldering iron for a few seconds.

Introduce some solder to the heated leg and continue applying the iron, moving back and forth on the leg. The enamel will begin to separate from the copper and bobble.

Continue adding solder until the leg is silvered all over. You will have to turn the coil over as you do this to ensure coverage. Coax any surplus solder and enamel to the end of the leg.

Repeat the procedure for the other leg. When complete, snip of the ends of the legs, with the surplus solder attached, leaving at least 1cm of straight leg before the turns.

Step 5: Completed Coils.

Your completed coil should look like one of these. and can be inserted into a 1.5mm hole in a PCB. For Niftymitter, the transmitting frequency of the transmitter can be increased by increasing the separation of the turns of the coil. This can be achieved using the head of a small screwdriver to manipulate the gaps.

Comments

author
rahulradhamandiram (author)2017-04-25

I would like to wind a 17 micro Henry inductor. Maximum current of 30 A is epected without saturating the inductor. Which is the best way to go? Please reply

author
vipin joseph (author)2017-02-21

How to I make 400micro Henry and 200 micro henry inductor plz give and in my email id knownlight@gmail.com

author
7757 (author)2016-08-16

How to I make 8.6 micro Henry inductor plz give and in my email id
parthkadiya772@gmail.com

author
RajanC3 (author)77572016-11-03

do you got how to make that much henery inductor? please mail me rajanchalotra23@gmail.com

author
elarcosadimple (author)2016-08-24

Hi! Can you help me make 400-500uH? What diameter of wire should I use and how many turns does it have? Thank you for your help!!!

author
Suresk kumar (author)2016-04-01

How to find inductance

author
ManojA11 (author)2016-03-31

hey any one tell me the required length,diameter, of 3.2nH inductor . and tell me how can it made own

author
nico.botha.94 (author)2016-03-05

Hi All, being brand spanking new to this, i have a question........how do you know which guage wire, and how many turns to use for a coil ?, say for eg, i want to boost 12vdc to 20vdc with a coil, trans and caps....how now do you calculate the guaging and number of turns of the wire for the coil ?

author
mafzal.qureshi.3 (author)2015-04-25

hi, which type of wire and no. of turns is used for 0.1uH inductor for FM transmitter?

author
TiagoN2 (author)mafzal.qureshi.32015-12-15

use the same wire, 8 to 10 turns using a pencil

author
okunnnnn (author)TiagoN22016-02-27

what type of pencil ?
moggol 2 ?

author
Markeedoodoo (author)2015-02-05

hello, what type of wire can you suggest in making 200uH inductor for AM transmitter?

Cheers!

author
Arghus (author)2014-05-17

i was thinking of induction coil to heat the soldering iron point, but i am afraid it would short, is all i need a 220v diode or 2 perhaps?

author
royshearer (author)2014-02-26

Sorry to say I'm not familiar with the types of inductor you are describing (axial lead inductors?). I suspect there is a reason for choosing one over the other, as the transmitter circuit I have worked with did specify an air core conductor.

author
techno guy (author)2011-05-17

How can I make a 1 milihenry air core induction coil? It's for an EMF detector that I might make into an instructable.

author
Bharat garg (author)techno guy2013-10-24

check this out
http://www.crystalradio.net/cal/indcal2.shtml

author
infanati (author)2013-07-23

Hi, im working on a project at the moment and im wondering how would you go about wiring 2 coils together. One being the inductor and the other the collector. so that the electricity one flows one way. Into the collector and straight out the inductor.

author
royshearer (author)infanati2013-07-23

I'm afraid I can't help you there, not sure about that!

author
mrmerino (author)2012-12-19

How much inductance do these little guys have?

author
royshearer (author)mrmerino2012-12-19

we're not sure - see comments below!

author
JakeTobak (author)2009-12-01

I don't know if it would be more or less work, but you could probably also sand paper the enamel off.

author
royshearer (author)JakeTobak2009-12-14

I had a shot at burning off the enamel and then sanding clean, but still had to work the coil with the soldering iron to get it to tin. Any tips?

author
steveastrouk (author)royshearer2011-12-27

Scrape it with a knife blade is more effective than sandpaper.

author
t.rohner (author)royshearer2009-12-26

At 100 MHz the current flows only in the outer 10 micrometers of your wire. This is due to the skin effect. So normally i would take a silver plated copper wire for a air coil of this dimension. The windings have to be apart anyway, so i makes no sense to take enamelled wire. By using silver plated wire, you have a lower resistance in the skin region and you don't have the hassle with tinning.

author
burdockwing (author)2011-04-15

what does an induction coil do?

author
royshearer (author)burdockwing2011-04-15

That is a good question. I didn't know, but typed your question into google and read this forum page and now have a slightly better idea!
http://www.physicsforums.com/archive/index.php/t-101306.html

I think inductors are kind of like flywheels, in that, they resist being activated, and resist being deactivated. So when current is applied, they take some energy and put it into their magnetic field, slowing the increase of the current. And when the current to them is decreased, the magnetic field acts to keep current going, slowing that decrease. Hence their use in AC circuits almost as dampers.

Capacitors behave in a similar way, but resist changes in voltage rather than current.

I've also realised that what I've described making hear is not technically an induction coil, but an 'air core inductor'.

author
Blofish (author)2010-01-07

http://www.66pacific.com/calculators/coil_calc.aspx

inductance calculator

author
agis68 (author)2009-12-02

 how do you know the appropriate length and spiral step of any of the coils you ve made??? Do you have any LC meter? be explained 

author
royshearer (author)agis682009-12-02

I am simply using the specification from Kogawa's transmitter page here. He does not give an inductance for the coil, I would love to know how to measure it, or a refresher on how one calculates the spec for a coil for a given inductance.

author
revelae (author)royshearer2009-12-05

1.598E-002 microhenries, is what this site gives.

author
royshearer (author)revelae2009-12-14

cheers!

In practice, I find I need to separate the windings of the coil to get the frequency of the transmitter up, so, assuming the coil is 0.8 cm long, I get an inductance of 3.841E-002 microhenries

author
agis68 (author)royshearer2009-12-03

electronics-diy.com/lc_meter.php try this you can find it also assembled 

author
hivoltage (author)2009-12-01

 I like to use my mini torch to burn off the enamel, followed by light sandpaper to get rid of the soot. Makes for a nice clean copper surface that solder tins very easily, especially if you use a little flux.

author
royshearer (author)2009-12-01

I have tried sanding/ filing but its awfully fiddly and one has to spend as much time tinning anyway. Shall try the lighter method though, cheers. This is a collaborative instructable so just message me if you would like to augment / correct anything in it.

author
mothflavour2 (author)2009-12-01

I find burning it off with a lighter is the best way.  This works really well on headphone wire.  It also gets rid of the reinforcing fibres.

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