inductance question

Yzordderrex a écrit :

NEO! It isn't just one big turn :-)

What you're after is called a Brook's coil. The very nearly optimal coil has a square section (a x a), internal diameter 2a (and consequently external diameter 4a ). You'll have to solve this for your wire length and diameter.

Inductance value is L = 2.55E-9.a.N^2 (in H) with a given in mm.

--
Thanks,
Fred.

"Fred Bartoli" wrote in message news:467154ce$0$31412$ snipped-for-privacy@news.free.fr...

Sweet!

Expect lots of interwinding capacitance.

A one-turn coil, by the way, makes a nice antenna when it gets to be one wavelength in circumference -- think "loop antenna".

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Square section?? Is that why those wallwart transformers have square bobbins?

D from BC

square in cross section. wound round.

He'll get more inductance by tightly bundling those turns=20 than by winding them is a single layer solenoid of the same=20 diameter. The bundled form provides tighter coupling=20 between the turns, that most closely approaches the turns=20 squared effect on inductance.

The inter winding capacitance will be higher, also. I don't=20 know exactly what the optimum relationship between bundle=20 diameter and average turn diameter for optimum inductance=20 per wire length, but I am guessing that the bundle cross=20 section diameter needs to be quite a bit less than the=20 average turn diameter.

Just one of many web pages on the Brooks coil:

Making the cross section circular or hexagonal rather than square increases the inductance by about 1%; hardly worth doing.

If you want to get the highest inductance and the highest "q" and at the highest possible frequecny:

then you want a shape that incloses the maxium volume, with a minimium shaped wire envelop I geomtery tis wold yield a sphere. not so goo for coils.

the next shapoe woulb be apporx 2:1 right hand clynder shape,with several turns, and the angle of wires about 42 degrees....

Marc

1% more is more. By the way, do you have a reference that confirms this magnitude of improvement for a round copper cross section? I would have guessed a couple more percent, because it reduces the number of longest turns (that use the most of the total wire length per turn) and the shortest turns (that enclose the least area) and increases the number of turns near the average length, Reducing the shortest flux line that encircles all the turns, as well as reducing the distance between each turn and its average neighbor, improving their flux linkages. I would be a bit surprised if all those slight but compounding factors added up to only an additional percent.

Right hand cylinder?

Is it like this

| ----/////////-

1 ---/////////-- 42deg angled windings | --/////////---

D from BC

Courtesy of Google, I see that Brooks inductors were discussed on SED back on August 25, 2004, where you asked Winfield about circular cross sections.

Winfield mentioned a "definitive" study of Brooks inductors, but apparently nobody has ever posted it.

I'm going to take a chance that your email address is jpopelish at rica dot net and send it to you.

I put up with all the spam just to make it simple for nice people like you to send me stuff. Thanks.