Wire gauge ?

[swmomark]

I am working on building a 14"x18" DD coil. I am waiting on a inductance meter I ordered, but would like to try and get started on the larger coil. I am getting my original inductance and resistance from a 10 1/2" DD coil from the same detector that I want to put the larger coil on. Right now I know the resistance and length of one side of the smaller coil. The length of the side of the coil I have checked is 134ft. To get the same resistance and inductance on the larger coil, do I need approximately the same length of wire and gauge. I am wanting to get close to the right amount turns etc. until my inductance meter gets here. Any input would be appreciated. Mark

[simonbaker]

coil calculator

I would try this coil calculator.

http://www.captain.at/electronics/coils/

Go down to where it says: "Number of turns calculation". Use multi-layer formula and guess at the cross section of your coil, maybe 1/4" by 1/4", which means outer diameter is X and inner diameter is X - .25", length is .25".

You have to make wild guess for diameter because of D shape. If single-D is 18" x 9" approx, for equivalent round coil maybe try (18 + 9) / 2, maybe 12 to 14 inches?

Regards,

-SB

[Qiaozhi]

I would try this coil calculator.

http://www.captain.at/electronics/coils/

Go down to where it says: "Number of turns calculation". Use multi-layer formula and guess at the cross section of your coil, maybe 1/4" by 1/4", which means outer diameter is X and inner diameter is X - .25", length is .25".

You have to make wild guess for diameter because of D shape. If single-D is 18" x 9" approx, for equivalent round coil maybe try (18 + 9) / 2, maybe 12 to 14 inches?

Regards,

-SB

Have you tested the accuracy of this calculator? Unless I'm mistaken, it appears to be based on a variation of Wheeler's equation, which is for solenoids and not for large air-cored coils. In fact, I've just noticed that it states on the web page: All calculations apply to solenoidal (cylinder) coils only!

In practice these calculators tend to over estimate the value of inductance. So, if you calculate the area enclosed by your D-coil, and then recalculate the radius for a circular coil based on that area, you can use those values in the calculator. When the circular coil is formed into the required D shape, the inductance is usually close to the desired value.

[simonbaker]

Have you tested the accuracy of this calculator? Unless I'm mistaken, it appears to be based on a variation of Wheeler's equation, which is for solenoids and not for large air-cored coils. In fact, I've just noticed that it states on the web page: All calculations apply to solenoidal (cylinder) coils only!

In practice these calculators tend to over estimate the value of inductance. So, if you calculate the area enclosed by your D-coil, and then recalculate the radius for a circular coil based on that area, you can use those values in the calculator. When the circular coil is formed into the required D shape, the inductance is usually close to the desired value.

I agree. I tried some of these calculators on some circular test coils I have and I couldn't get good agreement. In my cases, they underestimate. So probably best to find someone who has made same coil you are working on.

I'll keep looking around at calculators, see if any do better on my test coils.

Cheers,

-SB

P.S. Another calculator I tried here: http://www.66pacific.com/calculators/coil_calc.aspx

[Qiaozhi]

I agree. I tried some of these calculators on some circular test coils I have and I couldn't get good agreement. In my cases, they underestimate. So probably best to find someone who has made same coil you are working on.

I'll keep looking around at calculators, see if any do better on my test coils.

Cheers,

-SB

P.S. Another calculator I tried here: http://www.66pacific.com/calculators/coil_calc.aspx

Actually you are correct ... these calculators tend to underestimate the inductance, not the other way round. I got myself a little confused there. All seems ok when the coil is measured on the winding jig, but after removal and tightly binding the wires, the inductance always ends up higher than expected. However, if you're constructing a DD coil, then reforming it into the correct shape lowers the inductance to the correct value.

[Qiaozhi]

Coil Calculator

I've put together a coil calculator written in HTML/Javascript and attached to this post.

This calculator is based on Brook's equation, rather than the one from Wheeler, which is aimed at calculating the inductance of solenoids.

A Brook's coil is a special case of a circular coil inductor of rectangular cross-section, that is designed to achieve the maximum inductance for a given length of wire. An ideal Brook's coil has a square cross-section and the inner diameter is equal to twice the height (or width) of the coil winding. However, these ratios are not critical, and you can have a coil that deviates quite significantly before the inductance moves too far from the correct value. I have found this calculator to provide more accurate estimates than the one's based on Wheeler's equation.

The program will run under Windows, Linux or Mac using your preferred browser (Firefox, Internet Explorer, Epiphany, Sea Monkey, whatever). Double-click on "coilcalc.htm", or start the browser and open the file from there. There are no instructions, as it should be intuitively obvious ... famous last words.

Any comments welcome.

[Qiaozhi]

Coil Calculator

Oh yes ... forgot to mention, if you enter rubbish in the input boxes you'll probably see "NaN" appear in the results. For those not initiated in the joys of Javascript, this means "Not a Number".
So, as usual, rubbish in means rubbish out.

[Tinkerer]

Oh yes ... forgot to mention, if you enter rubbish in the input boxes you'll probably see "NaN" appear in the results. For those not initiated in the joys of Javascript, this means "Not a Number".
So, as usual, rubbish in means rubbish out.

Hi Qiaozhi,

I tried the coil calculator above, using Google Chrome, the page opens fine, I fill in the numbers and that is it, nothing happens, no button to GO or anything.

I have been using the MiscEL coil calculator.

Tinkerer

[simonbaker]

Oh yes ... forgot to mention, if you enter rubbish in the input boxes you'll probably see "NaN" appear in the results. For those not initiated in the joys of Javascript, this means "Not a Number".
So, as usual, rubbish in means rubbish out.

Very nice, thanks for doing it.

It seems to over-estimate inductance on my test coil about 50%, where the other calculators under-estimate by about 50% -- maybe I can average the two.

It would be nice if you could paste a conversion chart of wire gauges to diameters on the page -- I've seen some around. Or even provide a wire gauge input option as alternative to wire diameter.

Have to say, my test coil may be a problem. It is actually the outer coil of an experimental concentric coil I made. The inner coil is unconnected, I didn't think it would contribute to the measured inductance significantly.

I think it is worth staying with this to see if we can get a formula that really is accurate for our coils.

Cheers,

-SB

[Qiaozhi]

Very nice, thanks for doing it.

It seems to over-estimate inductance on my test coil about 50%, where the other calculators under-estimate by about 50% -- maybe I can average the two.

It would be nice if you could paste a conversion chart of wire gauges to diameters on the page -- I've seen some around. Or even provide a wire gauge input option as alternative to wire diameter.

Have to say, my test coil may be a problem. It is actually the outer coil of an experimental concentric coil I made. The inner coil is unconnected, I didn't think it would contribute to the measured inductance significantly.

I think it is worth staying with this to see if we can get a formula that really is accurate for our coils.

Cheers,

-SB

I'm surprised you report that it over estimates by 50%. I've used this equation a lot, and it's reasonably accurate. What numbers did you put in the input fields?

[Qiaozhi]

Hi Qiaozhi,

I tried the coil calculator above, using Google Chrome, the page opens fine, I fill in the numbers and that is it, nothing happens, no button to GO or anything.

I have been using the MiscEL coil calculator.

Tinkerer

Hi Tinkerer,

I've just tested the calculator with Google Chrome and it's working just fine.
Please see the attached image. That's what you should see in your browser.
You need to click on the big Calculate button at the bottom to get the results.

A couple of other points:

1. You must have True Type fonts loaded (could be a problem on Linux. In which case you'll need to install msttfonts). In particular it uses Comic Sans MS. Without this font it will probably look slightly different, but should still work.

2. The browser must have support for javascript script and have Active Content enabled.

[Max]

buzz talk

Hi Tinkerer,

I've just tested the calculator with Google Chrome and it's working just fine.
Please see the attached image. That's what you should see in your browser.
You need to click on the big Calculate button at the bottom to get the results.

A couple of other points:

1. You must have True Type fonts loaded (could be a problem on Linux. In which case you'll need to install msttfonts). In particular it uses Comic Sans MS. Without this font it will probably look slightly different, but should still work.

2. The browser must have support for javascript script and have Active Content enabled.

can add some buzz talk ?

From a top-level view, the product assurance architecture is functionally equivalent and parallel to the Qiaozhi postulated use of dialog management technology.

Always the evil lure...

Kind regards,
Max

[Qiaozhi]

And here it is showing the results of a calculation.

Remember to be careful entering the inner radius. Don't put in the diameter by mistake.
Also, everything is metric. For you imperial types, there are 25.4mm in 1 inch.

[Qiaozhi]

can add some buzz talk ?

From a top-level view, the product assurance architecture is functionally equivalent and parallel to the Qiaozhi postulated use of dialog management technology.

Always the evil lure...

Kind regards,
Max

Very good.

[simonbaker]

I'm surprised you report that it over estimates by 50%. I've used this equation a lot, and it's reasonably accurate. What numbers did you put in the input fields?

Wrong ones!

Of course I put in diameter instead of radius.

Try again.

My coil is about 26 cm in diameter. About 111 turns. 30 gauge enameled wire.

D = 260 mm, R = D/2 = 130mm, Nturns = 11, wire thickness .2546 mm.

Lcalc = 8.111 mH
Lmeas = 12.3 mH

So now I'm back to underestimating by about 30%.

Results for inner coil:

D = 155 mm, R = D/2 = 78mm, Nturns = 100, wire thickness .2546 mm.

Lcalc = 3.603
Lmeas = 4.24

Closer, but other calculators do better on it too.

Maybe I'm wrong about coil parameters. I'll have to wind some new ones carefully and try again.

Cheers,

-SB