A Revised Inductance Calculator

On Fri, 01 Aug 2003 11:18:13 -0700, Mark Fergerson Gave us:

I'll give you three guesses, and the first two don't count, and the third one doesn't either if the answer is yes.

Just did a spot check: asked for 0.01mH in a 1" diameter, 1" long coil, using 26 AWG wire. Got 0.0108mH at 26 turns.

The program I use tells me it should be very close to 0.0120mH.

For the RF work I do, I'll stay with a program that talks to me in nanohenries and estimates Q and SRF as well. I also find it most convenient to enter a winding pitch, instead of coil length, since highest Q will generally be for a wire diameter about half the winding pitch. I'd expect the web scrip would be useful for multi-layer air-core audio coils for crossovers and the like.

Cheers, Tom

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It looks like you are moving towards a finite element field solver. The computer can supply good answers on various 3D coil geometries, by solving for mutual inductance using Maxwell's 'Geometrical mean distance' repetatively applied to large numbers of points on a mathematical model of the 3D coil structure. The method is effective but slow and a ballache to programme. regards john

i downloaded Ansoft's (?) Maxwell SV -- a 2-solver where you input a cross section, but i don't see how it would be used to calculate M. it does a bunch of other stuff.

you're right, i think. it is a type of FEM solver. i can even see the solution or how the integral would be set up for a triple integral, i just can't get the equation. haven't had much time to really look at deriving my own, either.

BRs, mike

Never could manage silent and deadly. Deadly, yes.

Yes, please.

Mark L. Fergerson

This site:

has a lot of references about the general subject, including some for spiral inductors.

Totally OFF TOPIC:

I Couldn't get any pictures of the fire, about 2 miles away, too high of a mountain blocking my view.

But I got some of one of the Hellicopters that was hauling water to the fire. Pictures 1 to 8 are taken from town site (Elev 728 Meters), the balance are from near the top of another mountain. Elevations are shown in names. Some nice scenery pics also.

If interested, take a look.

Take care....Gary

nice looking hills. BR, mike

Me Also.....Brian

I've stuck 2 Gif's on A.B.S.E. Any problems and I'll be happy to email 'em direct. regards john

well, sorry. the OP was pretty much blowing off suggestions to make the thing better. same with me after i was decent enough to try it and submit my 2 pfennig.

got smart again, real soon and tried Gary's twocoils and solnoid3 :-) pretty decent little dos apps. looks like twocoils returns a good enough approx of air core M to finish off an analysis and build. it just doesn't agree with solnoid3 on inductance for a given coil, but if you put those numbers in the OP's calculator, his gives a result close to twocoils, but would be better with nH accuracy.

wire manufacturers. never checked. it'd be a good way to test other calculators, i'd think. of course, there's a fair amount of other little sites where you can find stuff like that. but a mfg's tools would be easier to find and on the money. magnetics mfgs have a bunch of resources, also. thanks.

br, mike

news://dp-news.maxwell.syr.edu/alt.binaries.schematics.electronic

Astraweb is still free 50 MB/day, but if you try to use more than one free account at the same time, there will be an IP address match and both/all of your free Astraweb accounts will be de-activated. They say "you are only allowed one free account" and they mean it.

Here's a place to get a free account at Newscene, no CC needed:

Strange, I only see one gif there, page 181 from Grover.

Thanks, - Win

I don't even see one yet (14:32 UK time).

Are they contained in one post or two?

Thanks, - Win

I see two attachments. Sadly, they are both in GIF and Acrobat assumes there is 72 pixels/inch in this case, so it won't OCR the text for me. If these were scanned into TIFF, with the resolution per inch at say 300 DPI, I could try and OCR scan this text and clean it up some. But other than that, they are quite legible.

Jon

Jon. The GIF pages were scanned 'line art' at 300dpi. I'll see if I've got a bitmap converter that'll do a GIF to TIFF. regards john

I know. My Acrobat tools has the ability to do OCR (so they say, anyway) for anything done between 200 and 400 DPI. Which is exactly what you did. But GIF doesn't contain the number of pixels for each inch in its format, so Adobe (apparently) assumes that the DPI is 72. Natually, it claims you scanned in a "darn big page" and claims that the pixels per inch is bad.

TIFF includes that information in it. But I'm not sure what happens if you just convert GIF to TIFF. Probably nothing good.

Jon