Inductor winding question

[Jimmy154]

When winding a inductor how big should the air core in the middle be? Does it matter what size it is?

I know there are on-line calculators that recommend how big the radius in the center should be and at what height you should wind them.

If for 1.5 mH inductor an on-line calculator recommends a 2.2" radius and you make it 1" instead what are the drawbacks?

[454Casull]

You'd probably get a different inductance.

[DrSplodge]

As far I can recall, if you make the radius of the air core smaller, then you will get a more concentrated electrical/magnetic flux flowing throught the middle of it.

This probably won't matter too much, unless you have EFI sensitive devices nearby.

Just another note, if you are using more than one inductor, it would be a good idea to strategically place them so that their fields cancel each other out. Again, this won't matter so much if there isn't anything sensitive nearby, but it if good (and common) practice amongst speaker manufacturers.

[DrSplodge]

Oh yeah, and make sure you check the inductance too : )

Use a multimeter that is capable of doing it...

[Bill Fitzpatrick]

Originally posted by DrSplodge
Just another note, if you are using more than one inductor, it would be a good idea to strategically place them so that their fields cancel each other out. Again, this won't matter so much if there isn't anything sensitive nearby, but it if good (and common) practice amongst speaker manufacturers.

No, you place them so their fields do not interact with each other.

[DrSplodge]

Yeah, sorry.

You should place them so that the fields do not interact with each other.

[ashok]

You can design your own air core inductors using a free software program.
It works well and is easy to use. You can also check what effect different core diameters have on your winding. Mainly to do with coil size and DC resistance.

Go to the Audiosoft site - the providers of Calsod software. The inductor design program is listed as a free download in the list near the bottom of the page. Click on it and it will download the program.

http://members.optusnet.com.au/~audiosoft/

Cheers,
Ashok.

[Jimmy154]

Thanks for your help. I know that if you make the radius of the hole in the center smaller it makes the DCR less in the end. I was wondering if making the radius of the hole in the center a little bigger has any advantages. Because I saw some seemingly high end inductors that left the hole in the center maybe a little bigger than I was going to. I was going to use a diameter of about 25 mm in the center by 25 mm in height.

But I guess the conclusion is that there's no benefit to making the hole bigger, just winding ease prehaps.

[rherber1]

I have used the free program from Audiosoft (author of Calsod) and it gives very close results. Wind on a little extra and measure/trim to get the exact value. A suitable inductance meter for low cost is available from http://www.aade.com/lcmeter.htm

The diameter of the core you select is largely dependent upon the wire size you are using. It is much easier to wind large gauge wire on a larger diameter core. Smaller gauges can easily be wound on smaller diameter cores. Up to 1.0mm wire diameter will be suitable for a 25mm diameter core but for larger gauges (over 1.0mm) I would go for a core diameter of 38mm.

[Ed LaFontaine]

Is it reasonable to adjust/tweak DCR by changing the I.D.? I need another project use for my wood lathe...Custom sized bobbins...maybe add a turns counter?

Also, I'd be interested in the sources for the wire to make these.

Thanks