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Badweazel

Exotic Woven Coils

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Hello,

 

Has anyone on here ever built any P.I. Coils? Attempting a high sensitivity small mono coil. Just looking for any tips and tricks anybody might have.

 

Coils are typically wound as cylinders with a foam core. I think it might be possible to build something comparable by hand. Going to try some coils made with known exotic coil weaving techniques first.

 

Coils such as the Nugget Finder Sadie are really good. If I can come up with something that will be a bit better I will case it in ABS Plastic like a production coil for field testing. Probably a boondoggle that will not get any traction.

 

Here is what I am trying now.

 

3.25" ID

5.75" OD

.375" Thickness

304.2 uH

Wound in 660/46 Litz Wire

 

Cheers,

Mark

 

post-38580-0-47715000-1426036442_thumb.jpgpost-38580-0-99398600-1426036604_thumb.jpg

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Well I don't know enough about electronics to know if it will work or not, but it sure is pretty. You just never know.

 

I remember John Kah, the founder of Coiltek once said, building coils is 50% electronics, 25% design, and 25% voodoo and black magic. He said the 25% voodoo and black magic are those times when you do something really off the wall just for the hell of it and beyond all explanation; you end up with an amazing coil.

 

Doc

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Doc,

 

Appreciate the encouragement.

 

I want to use the small mono coils out there now as a performance yardstick. Did you ever use one of those 3 1/2" probes? The potato masher looking one. How did they compare to a 6" round mono?

 

Thanks,

Mark

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Mark, interesting concept for a coil's winding, of which I know nothing about the technical aspect of making a coil, but I would love to hear the outcome, good or bad!

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Chris,

 

Thanks for the tip. Appreciate any help since this is a first try at a small coil and I think they are the toughest to do right.

 

My general ideas and intent are as below. Anyone who has any thoughts on where and why I am off track please let me know. It could save me a lot of wasted effort. Crowd sourced ideas always get close to the correct answer pretty darn quick.

 

Trying for a coil optimized for a Minelab GPX5000 operated in the fine gold timing. Just trying to keep my rig somewhat competitive with the newer gear that is reported by you and Steve H. to be demonstrably better on short time constant targets like specimen and small bits. Want the best little coil I can get to tuck into the tight spots that 14" X 13" Semi Elliptical Super D can't get to.

 

Talked to a manufacturer of coils who told me he uses 300uH inductance and 0.5 ohms resistance for Minelab P.I. Coils. So I am shooting for those numbers as my nominal. Pretty close with this first try. I have read second hand reports of a range from 265uH to 380uH reported in Minelab P.I. monocoils. Does anybody know differently?

 

The woven coil minimizes undesired capacitance. It is an old technique. Litz (actually Litzendraht) reportedly implies woven or braided in German. Litz wire is woven and has insulated strands to lower capacitance and eddy currents between strands and windings. It seems contrary to use woven litz wire then wrap it in tight parallel windings seized with zip ties or waxed lacing. This creates a distributed capacitance throughout the coil. This likely a second order effect and probably tolerable in a factory built coil that is built to be serviceable yet affordable. Labor is reportedly the most expensive coil input. Weaving increases labor costs exponentially or more like "geometrically". The 660 strands of 46 gauge wire litz is also recommended by a manufacturer as what they are currently using in their best coils.

 

Tuning the coil, shielding, lead wire et al to my GPX5000 will be done empirically first by ear and ultimately with an oscilloscope if performance warrants it. More than one person has demonstrated a half dollar is detectable at 4' even with an old Minelab SD P.I. using an oscilloscope while nothing can be heard by ear.

 

Right now, I have a Coiltek 3 1/2" Probe, Coiltek 6" Round Sniper, Minelab 8" Round and Nugget Finder 8" x 6" Sadie as Monocoil performance yardsticks to better.

 

Ultimately my amateur attempt at building a sensitive small coil is likely futile, but the journey itself will be worth it to me.

 

Cheers,

Mark

 

P.S. : Still rereading your tome "FISTS", there are some uniquely great concepts and methods in there. Hope you will expound on some of these in a future book.

 

Warning: Do not attempt to operate a vehicle or heavy equipment while maneuvering through this excessively long post. The bloviating will result in drowsiness or unconsciousness in most individuals.

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The windings you are making are called "basket weave" type coils. Many pros have tried to make them work better than the usual bundle type of coil. The basket weave looks good in theory, but have failed to actually work better. But you might make something that works great. After all 25% of coil design as being better is luck.

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Clark,

 

Thanks for the info. I figured somebody must have tried something along these lines before.

 

"Bundling" is the cheapest manufacturing method for sure. If there is no great gain to any other method that's what will be used.

 

I am not trying to manufacture coils just build one better coil, even if only incrementally better.

 

There are some flat spiral P.I. Coils that have been produced as printed circuit boards to keep costs down. There are probably some other examples out there.

 

Can you point me towards some reading material on the topic? Know about the claims in Bruce Candy's litz wire coil patents and some forum posts but not much else.

 

Or a good contact?

 

Thanks,

Mark

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