Winding your own inductors

[Jason]

I'm in the process of winding my own crossover inductors, with varying results.

Compared to professionally made inductors of the same gauge and length, they tend to have lower inductance. The tighter packed the coil the better the results, so it seems and would make sense.

I had a look around the web for a coil winding reference/tutorial and didn't find much decent information other than that at http://www.lalena.com/audio/.

I was wondering if anyone had another reference or personal tips and tricks on the subject regards optimum sizing (in this case using 14ga wire and aiming for 0.24mh).

Thanks in advance,

Jason

[GRollins]

Jason,
Keep in mind that tighter packed means more stray capacitance between the windings, but yes, higher inductance.
The trick about winding inductors is that there are scads of variables. Worse yet, there are no standardized formulas. Sound weird? It's true. I've seen papers comparing five or six formulas and pointing out that the results were inconsistent. (I touched on this briefly in another thread, but didn't feel like making an issue of it; people look in a textbook, find a formula, and assume that it is *the* formula. There's no such thing. Not to mention, you'd think that [seeing as how we're now in the 21st century] we'd have a reliable formula for winding inductors. T'ain't so, unfortunately.)
Anyway, find a book with a formula and wind an inductor, but be prepared to spend a while fine-tuning it. Or drop by http://www.sound.au.com. I believe there's some info in the speaker section about inductors for passive crossovers (note that he also mentions, in passing, problems with inductor formulas).
As far as optimum, generally speaking you want the cross-section of the inductor to be approximately square. It'll be more efficient that way, since the magnetic flux will be more confined.
Broomsticks or other wooden dowels make good cores for transformers. There are plastic coil bobbins for sale, but it's difficult to find the size you need.

Grey

[Vivek]

I too have tried to wind my own inductors. The problem is the wire keeps bouncing back like a spring. I have had a really tough time trying to keep the wound wire in place. Any solutions?
Thanks for any help.

[Jason]

A hot glue gun did the trick for me, followed by some neat cable ties. The glue can then be easily peeled off.

[GRollins]

Vivek,
Some people use the packing tape with the fiberglass strings in it, but over time the adhesive tends to dry out and the tape comes loose. It might be a good while-you're-winding solution, though.
Overall, Jason's suggestion about cable ties is the best option short of an actual bobbin.

Grey

[Vivek]

I'll try both. Thanks for the help.