Help winding my own inductor?

Then the inductance is *independent* of the number of turns, by the definition of inductance (induction per unit current).

Damn, now you made me hungry.

- YD.

First hit on askjeeves (Litz wire weaving):

- YD.

Perhaps. I was simply doing a search in the Delphion database and filtered it back as far as the patent I referenced above. That pretty much covered the interesting issues of such cable. If there is a prior claim, I can't find it. A German name isn't evidence of German origins.

I have seen the definition of inductance as flux times area per current (1 henry =3D (1 tesla * meter^2)/amp)) but this gives my mind a snag. Perhaps you can straighten me out.

Lets say you have a large toroid core of infinite permeability with a small air gap sawed through it, and 1 turn through the hole. I measure the inductance and find x henries. So at 1 ampere, I have 1/2 x joules stored in the inductor and in the magnetic field in the air volume of that gap. I then saw the gap to twice as wide and wind a second turn through the hole, and get the same flux passing through this thicker but same area air gap, and still measure x henries. So by 1/2L*I^2 I still have the same energy stored in the inductor and in the air volume in that gap, but there is now twice the original volume of air stressed with the original flux. How can that be the same total amount of magnetic energy?

I read in sci.electronics.design that John Popelish wrote (in ) about 'Help winding my own inductor?', on Mon, 22 Dec 2003:

The formula is L = N x [phi]/I, where N = number of turns, [phi] = flux = flux density x area and I = current.

There are now two turns, so L = 2x. If you hadn't widened the gap, the inductance would have been 4x.

It isn't. The inductance has doubled. From L = N[phi]/I, we get

L = NBA/I, B = induction, A = cross-sectional area

B = [mu]H, [mu] = permeability of air, H = magnetic field strength

and H = NI/l l = length of air-gap, since the rest of the circuit has infinite permeability

So L = [mu]N^2IA/lI = [mu]N^2A/l

To get L back to its original value, with 2 turns instead of 1, we need the gap to be 4 times longer.

If we then do a similar substitution for the stored energy:

LI^2/2 = (N[phi]I^2)/(2I) = N[phi]I/2 = N[mu]HAI/2 = N[mu](NI/l)AI/2 = [mu]/2 x N^2I^2A/l

N^2 has gone up 4 times and l has gone up 4 times, so the energy remains the same. H, B and [phi] doubled due to the two turns, but dropped by a factor of 4 due to the longer air-gap, giving a net halving.

I read in sci.electronics.design that YD wrote (in ) about 'Help winding my own inductor?', on Mon, 22 Dec 2003:

Bunched (untwisted) and purely twisted wires are offered by some suppliers with the incorrect description 'Litz'. At least one supplier, found by Google, lists these as "litz" wires.

Litzendraht, ISTR.

Does this answer contradict your last one?

I said, "How about if you adjust the gap to hold a constant flux for a given current as you change the number of turns?"

And you answered, "Then the inductance is *independent* of the number of turns, by the definition of inductance (induction per unit current)."

I read in sci.electronics.design that John Popelish wrote (in ) about 'Help winding my own inductor?', on Mon, 22 Dec 2003:

Yes. I misread your question to mean keeping N[phi] constant.

I believe the correct term for this is 'progressive winding', when applied to a coil structure.

RL

I read in sci.electronics.design that R.Legg wrote (in ) about 'Help winding my own inductor?', on Mon, 22 Dec 2003:

There is wave winding and there is progressive wave winding, which is a development of wave winding to make coils which are very long compared with the diameter.

Progressive wave winding works by effectively mounting the waver wire guide on a stock driven by a lead screw, so that the wave slowly creeps along the former. When the desired length is reached, the lead screw rotation reverses.

I didn't find any hits on Google, but I think I know who invented it. If so, there should be a UK and a US patent dated in the early 1950s, probably. Certainly, we had the machine in our model shop in 1958.

Thanks for the help. It makes a lot more sense, now.

Guys, guys, guys!

If you feed the trolls, they come back for more.

Let's stop playing "I'm righer". It's obvious who's got the wisdom that comes from years of experience. You've made your statements. Let the jury of your peers (and we beginners, too) retire in peace to ponder the evidence.

Peace,

On Sun, 21 Dec 2003 13:30:56 -0600, John Fields Gave us:

Not true. They must be isolated from each other electrically, except at the terminations. I said that. I know WAY more about it than you do.

On Sun, 21 Dec 2003 13:42:53 -0600, John Fields Gave us:

Try it... How many #22Ga wire strands does it take to make one 19Ga wire?

You lose.