Square Coil

[Geo]

Hi all. Long time ago i constructed a square coil 60x60 cm for delta pulse. I wrapped 21 turns (if i remember good). I measured it and the meter says 780uH. Yesterday i wrapped other 5 turns and the meter says 985 uh. I am afraid that the meter don't read good so i want (if someone remember:confused: ) to give me the formula to calculate the square coil

[Leto]

Square coil calculus

Have found this googling:
http://www.technick.net/public/code/...uctance_square
or this:
http://emcsun.ece.umr.edu/new-induct/square.html

[Geo]

Have found this googling:
http://www.technick.net/public/code/...uctance_square
or this:
http://emcsun.ece.umr.edu/new-induct/square.html

Thanks Leto. But i have problem. Lets go: turns=22, w=60cm, a=0.035cm (0.7mm diameter), mr=1 (i suppose that the Mr for air coil is 1. It gives me 1550uh or 1.55mH. The inductance meter reads 780uH. 1.55mH seems too big for me.
Another experiment. Coil of Delta Pulse is 1.1x1.1 m and 16 turns. so we have. N=16, w=110cm, a=0.075 cm mr=1 and L=1468uH. Ohh the coil 1.1x1.1m with 16 turns and 1mm wire has lower inductance than the coil with 22 turns 60x60 cm and wire 0.7mm.
What are you say?
Any Idea?:confused:

[Leto]

square circle

Sorry Geo I also assumed that mr = 0.999999 and got strange results as you do. Stupid me for not checking this and bad reputation for university of Missouri.

maybe this thread here will help
https://www.geotech1.com/thuntings/s...ead.php?t=6868
look for garys post

from Ham Radio magazine:
You can use the formula for self inductance, by translating the square into a circle (ie: the length of all four sides equaling the diameter).

First, find the mean radius.

A=(Len * 4) / PI / 2

A= the mean radius
Len= the length of one side of the square
PI= 3.141


Then use it to find the inductance of the coil.


(N * A)^2
------------- =L
9A + 10B

L= inductance in micro Henrys
N= the number of turns
PI= 3.141
A= is the mean radius in inches
B= the Length of the coil, in inches (not WIDTH !. Two turns at two turns per inch = 1 inch !)

Hope this helps.

[Leto]

software

Geo check this little free software:
http://www.miscel.dk/MiscEl/miscel.html
for download click upmost line

I'm really suprized..and it has square coil calculator too:
components -> air coil -> kind/loop rectangular -> analyze

[Radioactive]

What size wire? Wire size matters, I always use size 30 (AWG), so as I experiment and change size and shape I know as the uH (Z) changes it's not because of the wire size. Also the way it is turned matters. The best way to control and check is with a dip meter. This way the loop is resonated and you can check the frequency. I use two types, an older heathkit I've owned for 30 years, and an MFJ Antenna Analyzer. I used to own a HP Vector Network Analyzer but had to sell it, needed cash. So I could not afford one again ( I got it while working at Motorola as an employee sale) since they go for about 10 to $20,000. I found another way to do the tuning of the coil you might try. You need a signal generator and a spectrum analyzer. You find the exact frequency of the pulse from the detector. Generate this frequency (CW) through the loop. Then tune the analyzer to the freq. and use a wood or fiberglass pole to hole it away from any metal and keep making adjustments and checking for a greater signal strength. The formula's just get you close, where the resonance after it is tuned is ideal. I checked a few coils from manufactures and found large differences in the resonance frequencies between the receive and tx coils. Some were so off it was really bad. It's like using near non-resonance antennas that are a miss match, which degrades the performance. I guess I look at ait a different way as an antenna, then the others, as I am an RF Engineer.
I hope that helps you make a better search coils in the future.

[Geo]

Let's go again. Let's convert the square coil to circle.Perimeter of the 60x60 coil = 60x4=240cm
perimeter=2*pi*r so r=perim/2*pi = 240/6.282 =38.2 cm.
coil diameter=38.2*2=76.4 cm =30.07in
Now from Gary's site (Inductance calculator, august 2003) we have:
Coil inside diam=30.07in
wire=20.5 AWG
coil length= 0.3in
L=0.722 mh
It is near with my inductance meter and far from technick.net calculate for square coils.
Now lets try with technick.net formula.
N=22
R=0.382 m
a=0.0005m
mr=0.99999
L=1.56mH:confused:

Smething is wrong. Lets try the other foormula as Leto wrote.
(N * A)^2
------------- =L
9A + 10B

L= inductance in micro Henrys
N= the number of turns
PI= 3.141
A= is the mean radius in inches
B= the Length of the coil, in inches (not WIDTH !. Two turns at two turns per inch = 1 inch !)

L=(22*15.04)^2/(9*15.04+10*0.3)=109481/138.36=791uH

It is near with my inductance meter (780uH)

OK. I will keep this size. So the other times i will believe everythink that shows the ind.meter.
Thanks Leto

Now for radioactive. Yes the dip meter is very good solution but this time i have not one. It is very easy to construct one but the main problem is the calibrate of indications
My Regards
Bye

[bbsailor]

Geo,

Here is a little trick that I use to calculate inductance.

1. Accurately measure the outside diameter (OD) of the wire (including the insulation).
2. Multiply the wire OD times 5 for coils of about 20 turns to get the wire bundle diameter.
3. Use this wire bundle diameter as the coil length.
4. Use this online calculator: http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi
5. Use the 1 percent answer.

This method provides inductance calculation answers that are very close to my measured values from my "Almost All Digital Electronics" LC Meter. See my review of this meter, for making PI coils, in the Geotech General Electronics Forum (look at all postings from beginning to see it as it is a little old now).

When I plug 21 turns, 772.1mm diameter and 7.62mm length into this calculator, I get 1177uh. If I reduce the coil turns to 13 and make the coil length smaller to account for fewer turns, 5.08mm length at 772.1 diameter, I get 484.3uh. I don't know the size of your wire so you need to measure it and input the coil length as I suggest.

The accuracy of these calculators is very sensitive to variations in the coil length input factor. Wire with thicker insulation will produce a coil with less induction than wire with thin insulation. That is why I multiply the wire diameter in coils of about the 20 turns by 5 to obtain a good coil length which gives me consistent calculated output results compared with my actual LC meter readings.

Go to the following web site to see a full list of wire bundle sizes from 1 to 61 turns. http://www.raychem.com/US/datasheets...Entry_Size.pdf. This chart is very good if you must fit your ID wound coil into a coil housing that has a maximum coil outside diameter that must fit inside the coil housing.

This should help with your coil calculations.

bbsailor

[bbsailor]

Link update

OOPS,

Here is a link update for the wire bundle table. http://www.raychem.com/fetch.asp?fileid=980&docId=846

bbsailor

[Geo]

Thanks bbsailor. I will keep the formula that Leto sent me because the results are near the indications of my digital inductance meter.

(N * A)^2
------------- =L
9A + 10B

L= inductance in micro Henrys
N= the number of turns
PI= 3.141
A= is the mean radius in inches
B= the Length of the coil, in inches (not WIDTH !. Two turns at two turns per inch = 1 inch !)
But anyway thanks for your interesting
Best Regards

[1843]

Coil Formula

Hi Geo,
Have you made the Hammerhead coil? If so, measure its inductance with your DIM and see the result.
I calculated its inductande by last Leto formula; The result was different! it gave me 345uH!
I am confused, by bbsailor suggested site and his explain I got about 500uH.
What is your idea?
Your DIM is bad or bbsailor's?
Regards

[1843]

bbsailor,
I think that if coil shape changes, inductance changes too.
Chang the HH coil shape to square,then by your DIM measure its inductance and tell us the result.
Your suggested site result is good for circular coils...
Regards.

[bbsailor]

1843,

A 10 inch diameter coil will have 31.4" circumference. A 10 square will have a 40 inch perimeter and have almost the same inductance as a 12.7 inch coil.

Changing the shape of the coil as follows, will change the inductance.

10" diameter, .25" long, 25 turns makes a 456 uH coil. A 10" square coil that is .25" long with 25 turns is the equivalent of a 12.7" diameter round coil and is 609 uH. These numbers may not be exact but they are close to what you would measure if you made them as I described.

bbsailor

[1843]

bbsailor,
I say that change the 10" coil itself shape to square... not make another coil square 10" x 10".
I believe that changing shape in each coil, will cause to change its inductance.
As I know, you say that coils with same perimeter( every shape ), have the same inductance...
Is it right?

I calculated the Geo's 27 turns coil by Leto formula...
Its result was different at Geo's DIM.. (about 1200uH!!!)
So, this formula is wrong!

(N * A)^2
------------- =L
9A + 10B

[Qiaozhi]

bbsailor,
I say that change the 10" coil itself shape to square... not make another coil square 10" x 10".
I believe that changing shape in each coil, will cause to change its inductance.
As I know, you say that coils with same perimeter( every shape ), have the same inductance...
Is it right?

I calculated the Geo's 27 turns coil by Leto formula...
Its result was different at Geo's DIM.. (about 1200uH!!!)
So, this formula is wrong!

(N * A)^2
------------- =L
9A + 10B

Changing the shape will change the inductance.