Calculating Wire Length for Spiral Coil

David King

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Sep 20, 2014, 8:18:45 PM9/20/14

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I need to wind a spiral (pancake) coil from 0.4mm enamel wire. The ID
is 20mm and the OD is 150mm.

What is the procedure for caluculating the length of wire needed?

I am not a math wizz, so an example would be much appreciated.

David King

Jeff Liebermann

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Sep 20, 2014, 8:27:45 PM9/20/14

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On Sun, 21 Sep 2014 10:18:45 +1000, David King <dk...@interphase.com>
wrote:

Google for "spiral inductor calculator".
For example:
<http://www.circuitsage.com/tools/tool_view&tool_id=34>
<http://www.circuits.dk/calculator_planar_coil_inductor.htm>
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Lasse Langwadt Christensen

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Sep 20, 2014, 8:33:05 PM9/20/14

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area of pancake is pi*75^2 - pi * 10^2 ~= 17357 mm^2

17357 / 0.4mm ~= 43392mm

-Lasse

Jeff Liebermann

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Sep 20, 2014, 10:03:53 PM9/20/14

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On Sat, 20 Sep 2014 17:27:45 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Sun, 21 Sep 2014 10:18:45 +1000, David King <dk...@interphase.com>
>wrote:
>
>>I need to wind a spiral (pancake) coil from 0.4mm enamel wire. The ID
>>is 20mm and the OD is 150mm.
>>What is the procedure for caluculating the length of wire needed?
>>I am not a math wizz, so an example would be much appreciated.
>>David King

>Google for "spiral inductor calculator".
>For example:
><http://www.circuitsage.com/tools/tool_view&tool_id=34>
><http://www.circuits.dk/calculator_planar_coil_inductor.htm>

Oops. 2nd try. I didn't notice the above didn't include the wire
length. This should work:
<http://www.deepfriedneon.com/tesla_f_calcspiral.html>
However, it assumes that you know the number of turns. So, I plugged
in the following numbers:
Inner Dia 20. mm
Number turns ---
Wire Dia 0.4 mm
Wire spacing 0.0 mm
I then tried different values for the Number of Turns until the Outer
Diameter was equal to about 150 mm. I ended up with 162 turns and a
length of 43.2 meters, which is fairly close to Lasse's calculation.

If you're actually going to build this coil, I don't think you'll be
able to obtain 0.0 mm spacing between turns. The 0.4mm (#38 AWG???)
might not include insulation thickness, lumps, kinks, and bends in the
wire. I suggest you experiment with what spacing you can obtain, and
use that value instead. (I'm also not a math wizz, but instead prefer
to measure things).

tim

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Sep 21, 2014, 2:04:48 AM9/21/14

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_This_ math whiz approaches problems like that by computing the wire
length needed, cutting off about twice as much as the calculations say,
then winding the coil. Often, I'll end up with extra. Very very rarely,
it'll be half the wire used. Sometimes I'll come up short.

If you need to know for production, measure the starting length and the
amount left over, and subtract.

--
www.wescottdesign.com

David King

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Sep 21, 2014, 4:01:03 AM9/21/14

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Thanks for the helpful advice.

i will now starting winding and allow for a bit extra wire just in
case.

David King

John G

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Sep 21, 2014, 5:35:50 AM9/21/14

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David King formulated on Sunday :

Why worry??
Just wind from the wire reel and cut off when you get there.
Surly you are not going to buy the wire down th the last millimetre.
:-Z

--
John G Sydney.

Jasen Betts

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Sep 21, 2014, 7:36:36 AM9/21/14

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On 2014-09-21, David King <dk...@interphase.com> wrote:
>
> I need to wind a spiral (pancake) coil from 0.4mm enamel wire. The ID
> is 20mm and the OD is 150mm.
>
> What is the procedure for caluculating the length of wire needed?

start with the area of a circle 150mm diameter , sutract the area of the 20mm
hole, divide by the width of the wire.

--
umop apisdn

--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---

whit3rd

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Sep 21, 2014, 4:48:48 PM9/21/14

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On Sunday, September 21, 2014 4:36:36 AM UTC-7, Jasen Betts wrote:
> On 2014-09-21, David King <dk...@interphase.com> wrote:
>
> >
>
> > I need to wind a spiral (pancake) coil from 0.4mm enamel wire. The ID
> > is 20mm and the OD is 150mm.
> > What is the procedure for caluculating the length of wire needed?

> start with the area of a circle 150mm diameter , sutract the area of the 20mm
> hole, divide by the width of the wire.

Yep, that's the way. It needs the EXTERNAL DIAMETER of the wire: if
'0.4mm' is the wire gauge, you'll have to measure the insulation-plus-wire.

Another quasi-empirical approach is to wind one, and weigh it. That includes
any stretching of the copper during the winding process.