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homefire

Twisting Up DIY Coils ?

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Ok, Here's the story.  I built a Surf Master PI from kit.  I had a original Surf Master Coil I planed on using.  It Sucked.  I built a simple Mono Coil and it doubled the detection on all targets.
This detector would be more then fine hunting beaches or ToT lots if you don't mind the Dig It All thing.  NO Were like a Gold Machine.     I Gifted it to a kid.

Next I built a Mini Pulse Plus.  This  This detector can handle being set to run down at or below 10uS of delay.  This has potential of a half Azz nugget machine.   I needed a Faster Coil to allow it to do so.  Faster meaning from Tx Pulse to Sample time.  The amount of time it takes the Coil to cancel the Fly Back voltage  , less time. 
I don't want to get into all aspects of that here.  I just want to know if some of you are interested in playing at making your own simple PI Coils. 
I'm not trying to produce a Mine Lab Machine here just a super simple PI that DOSE Have the potential to find relatively small Gold.   CHEAP,  Did I tell You I'm Cheap Skate ? 
I have the GMT as my primary Gold Machine.  I just want to play with the PI thing too. 


 At first I started Playing with Super Simple Mono coils.   Some came out sorry. Some not so bad.  Some Quite dang Good.
Next to speed up the Coils I learned about the Basket coils.  Thought I had it going until my third failure.  Still working on some but I just can't seem to Produce that good of a coil.
I got messing around with  my High Dollar coil forms and came up with something I've never seen anyone do.  A Stacked Basket coil. 


The Idea behind a Basket Coil is to lower the Coils inherent Self Capacitance that Boost the Fly Back Voltage and causes the coil to take longer to settle down after the Tx Pulse ends.  The Basket Coil dose this by putting more distance / space between the winding's of the coil lowering Capacitance.   Previous Basket coils use a radiated spiral wind.  Starting from the Inside progressing outwards.  This works most well in lowering the capacitance but it also lowers the Inductance some what.   A coil with Higher Inductance is better at detection of the Target signal but also contributes to the Fly Back Voltage.   This Stacked Basket Coil does the same thing in lowering the Capacitance in the same fashion.  Keeping the Winding's separated .  It seems to have a advantage over the Spiral Wind Basket in that the winding's produce a more consecrated target signal because of the formation of the coil shape.  The spiral type basket the winding's progress outwards and this tends to reduce the concentration of the Target signal.  Unlike the Spiral the Stacked keeps all winding's  perpendicular to the  in respect to the target signal.  More Winding's exposed to the signal gaining the ability to gather more of same.    The coil sees the target signal some what like a Mono would but without the Added Capacitance that keeps the Mono Coil from running Fast. 


This Geometry of coil has another beneficial quality.  The Generated Field is concentrated in the vertical plain.  Whats to say it detects more  below and above the coils then a Mono can.  DEEPER !  As more target signal of the same strength is exposed to more winding's at the same vertical plane I don't see how this could not translate to more target signal.  I have a New Oscilloscope that I need to test this with.  My old DIY Kit DSO 138 Scope was not up to the task.


Rant Over  LOL


My current Resources:


Free Wire.  I salvage  all my wire from Old TV sets.  The Degassing Coil being the primary source.  All Older TV with a Picture Tube has them  .  More Usable wire can be had from the Yoke Coils at the End of the Tube. One Degassing Coil provides enough wire to build at least three or four coils or more.   Some of the Newer TV's they used Aluminum Wire for the Degassing Coils.  It works fine too if you want to use the stuff.  I've made some decent Coils with it.  You just have to use Mechanical Spices sense you can't solder the stuff.  Not a Issue.


Wire Forms.   I started building my own and found it a royal pain.  Had to create a New Form for every Coil type I wanted.  Wicked Wanda the Wonder Wife solved that for me.  Out of the Blue she say, Eaaaaa!  What wrong with these ? 


https://www.walmart.com/ip/Darice-Easy-Knitting-Loom-Round-4pc-Neon/10727494


She Relinquished her set to the cause.
I have a 5"  7"   9" and 11" loom.
You can do Mono Coils, DD Coils and Yep, Stacked Baskets.

Test Equipment:   I have quite a gathering of decent equipment at hand.  As for coils I rely on one of the most low cost items at hand.  A $7.00    Test About All O Matic ! 


These things are Dirt Cheap.  Did I tell ya I'm a Cheap Skate ?
This thing will tell you any and all you need about a coil .
It can tell you the Inductance and resistance in a single test.


https://www.banggood.com/LCR-T3-Transistor-Tester-Resistance-Capacitance-Diode-ESR-SCR-Inductance-Meter-p-987971.html?rmmds=search


Coil Shell Housings.


There are a few people that produce them around.  My Favorite Mr Hays shut shop. 

A guy named DB Bowers makes some good ones for a reasonable price.


For the most parts I improvise.  Use Coil Skid Shell as housings, Old Coils dissected.  Bucket end the lot.  Only limited by your imagination on that one. 

 

Shielding.  I use the good ol Copper tape on all Mono Coils.  Cheap and it works fine.  Did I mention I'm a Cheap Skate ?

https://www.banggood.com/10mm-X-20m-EMI-Copper-Foil-Shielding-Tape-Conductive-Self-Adhesive-Tape-p-1107008.html?rmmds=search

 

I use Graphite spray on all others.  You can not wrap the Stacked or basket coils. 

 

Here are a few crappy photo's of my mess and some basic information to ponder.

I have everything needed to produce a DIY coil for my GMT that I'll tackle some time this winter I think. 

 

 

 


 

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XCoil2.1.jpg

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D-coils basics.pdf

D-FastCoil.pdf

0919171004.jpg

Edited by homefire
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WOW !!  :arrowheadsmiley:  You really covered a lot of ground there Homefire.  I can completely understand needing to stick to a budget and quite frankly, it's so much 'cooler' when you make something highly functional from 'trash'.  You've got some nice creations there.  :thumbsupanim

I started making coils for my White's SPP detector after buying a couple Miner John's coils and wondering if I could build a decent coil myself.  Probably the best resource available on this subject and relating to the TDI series of detectors is a gentleman by the name of Reg Sniff.  He was gracious enough to answer my requests and provide me with enough information that I was able to build several good working coils for my detector.  Reg also pointed me towards this great article:  www.geotech1.com/pages/metdet/projects/fastcoils/FastCoil.pdf

My background in machining and manufacturing helped considerably in the actual construction of the coils once I had a reasonable understanding of how a PI coil works.  After temporarily leaving my career to help raise my kids, building coils at home became a nice distraction from the household stuff.  Plus, after I had built a few coils, it became fun to see how professional I could make them look, and function,  by only using stuff around the house and items available at the hardware store with the application of my skill set.

I also purchased the kit and built a Mini Pulse Plus PI detector and the nice thing is, the coils are pretty much interchangeable between the SPP and the MPP.  I was able to find a used oscilloscope for $50 and learn to use it during the construction of the Mini Pulse Plus.  I had done some soldering when I was younger, back when Radio Shack was the place to buy stuff like this.  It was a lot of fun to take an empty circuit board and populate it with a bunch of electronic components and end up with a device that rivals a commercial detector as far as sensitivity and detection 'depth' are concerned.  The ground balance feature leaves something to be desired in mineralized soils though.  I think that's to be expected with a project like this, and why Minelab can charge the big bucks for their technology.

For anyone wanting to mess around with building a PI coil I would highly suggest the Fast Coils article (mentioned above) as a starting point.  I would warn against making anything and plugging it into your expensive commercial detector.  Minelab PIs have special electrical requirements and not adhering to those specifications will most likely result in expensive repairs.

Here are a few pics of what I've been talking about.

Luke

 

 

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I just hurt my brain reading this :idunno:

Got to give it to you two....your way above my level. :)

 

Tom H.

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Yep, it can be done  .  NICE work !  :4chsmu1:  

All PI Detectors are pretty much cut from the same mold as fare as the Front end is concerned.   If you measure a Minelab Coil your going to find them little to no different then a TDI coil.  This is why they can be used on each other.  The good thing about making your own is if done right your going to end up with a Better Coil for YOUR machine then came with it.  Production coils are  produced to work with in reason on production machines.  Building your own allows you to Damp and Tune the coil to Your particular machine.  This can be way more beneficial on VLF Coils.   VLF Coils  bring a whole other set of Values that need to be dealt with to the table.

Yep,  GeoTech is a Gold Mine un to it's self on this stuff. 

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Well hold on now....

You can use a Minelab coil on a TDI, but not the other way around.

The TDI doesn't put as much current through the coil as the Minelab does.  The TDI coils have greater than .5 ohm resistance.  The Minelabs require .5 ohm or less if I remember correctly.

Please verify for yourself before you decide to plug a TDI coil into a Minelab detector.

Other than that, we're 'on the same page', Homefire.  :D

Luke

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Didn't know that .  I just knew the ML coils worked on the TDI.  In any event if the ML is looking for Less then .5 Ohm and TDI coil having more would not let the Genie out of the bottle.  Errr Magic Smoke.  

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Expensive smoke....  :grr01:

That stuff about the resistance requirements was another one of those things Reg warned me about. 

I can't take credit for anything, just trying to pass good information along to the next guy.

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There is no doubt , these forums are educating for sure.

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  I've read some of Reg's stuff.  I thought he had a hand in that  Fast Coil PDF.  Eaaaaa    Yes, the information's all out there to be sure.  It takes some  Work to learn enough to ask the questions that may get your there.  LOL  

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  Some day I'd like to have a go with the Vacuum Molding shells.  I have everything laying around here to give it a try with one exception !  A Functional Oven  !   :ROFL:

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Gearing up to build one of the TGSL PCB's I have squirreled away.  Knocking off a quick 5" DD to get it set up when done.

This is what the Build Document Calls for.

Diameter: 255mm x 137 mm (one coil)
Wire size: .25mm (30 AWG) enameled         Tx approx 99 turns of wire.   Rx Approx 104. 
Tx inductance: 6.0mH
Tx resistance: 18 – 25 Ohms
Tx resonance - About 14.5 kHz
Rx Inductance: 6.5mH
Rx resistance 18 – 25 Ohms
Rx resonance with 15nF – About 16.1 kHz


I only had 28AWG at hand and Deviated from the Prescribed Number of winding's and Coil dimensions.

Only completed the Tx Coil this far.

I ended up with 166 turns of wire due to the Wire Size and Smaller Form.

Shield is Copper Tape.  Used it a pile on simple Mono Coils with good luck.  The stuff is a pain to wrap without tearing.  The foils not much thicker then the foil of a Gum Wrapper. 

As seen on my Chines Special Meter (Gotta Love those  Chinese characters for the mH, Eaa?)   I achieved the 6mH and Resistance required. .  Not seen is after foil it dropped to 5.97Mh.   This calculates out the machine should be running 14353.122 Hz with this coil.  My plan is to build one as described and modify the second to run twice the normal Freq .  30Khz.  If this works as Planed I should end up with something like a 30Khz LoBo. 

This Coil is only for Testing but may be the bases for a good Sniper Coil for the other machine, Eaa?

Start2.jpg

Start.jpg

Copper Tape Shield.jpg

RxCoilSpecs.jpg

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Well, I seem to be in the ball park with one of the coils I made. 

I popped together a mock up Tx section just as used in the TGSL detector I intend building soon.   Using this I can see what the coils is doing as opposed to just calculated. 


        Guess I need to order some wire.  28 AWG is close but no cigar.

As Per 101 Document:
Diameter: 255mm x 137 mm (one coil)
Wire size: .25mm (30 AWG) enameled
Tx inductance: 6.0mH
Tx resistance: 18 – 25 Ohms
Tx resonance - About 14.5 kHz
Rx Inductance: 6.5mH
Rx resistance 18 – 25 Ohms
Rx resonance with 15nF – About 16.1 kHz


Experimental Coil
5 inch coil form
28 AWG wire.
Turn count unknown.

Double Wire Strand  Experiment Fail

rx  13.8  Ohms    6.18  uH  Yeild   14.011  Khz     

Single Wire Strand
tx   22.1   Ohms   5.89  uH  Yeilds  14.365 Khz     Pretty Dang Close.  10 more turns would probably get it.  Ran out of wire.


Getting Educated.

 

TGSL Tx Osc Mock Up2.jpg

Single Wire Tx Coil.jpg

Double Wire Receive Coil.jpg

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Homie

Have you ever tried Teflon coated wire?

AzNuggetBob

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Yes on PI coils .  This is VLF. 

LOL, on the PI coils your trying to keep the winding's separated best you can.

On VLF Coils your trying to keep the winding's packed as tight as you can to gain Inductance and use less wire.  Inter winding Capacitance is not a issue on these basic coils.  

Edited by homefire

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On 9/30/2017 at 5:43 AM, homefire said:

Yes on PI coils .  This is VLF. 

LOL, on the PI coils your trying to keep the winding's separated best you can.

On VLF Coils your trying to keep the winding's packed as tight as you can to gain Inductance and use less wire.  Inter winding Capacitance is not a issue on these basic coils.  

I agree Homie. I learned a lot from Reg as well and most people dont realize the thickness of the teflon is very important too.
I'll just say this
If you want to build your own coil but not sure about the ohms just put an ohm meter on the factory or after market coil.
As I recall the older Minelab PI's are around 4 ohms. you can get a lot more depth with a custom coil. one of my larger mono coils got to the point I had to replace the metal buckle on my hunt belt with nylon. every time I swung the coil I would hit it. At first I put a lower coil extension on the handle to get it out further away from me but that proved to wear down my back holding it up. also had modified it to hip mount, had to put it in a plastic housing, chest mount it and toss the factory aluminum housing in the parts pile. :2mo5pow::D but I did also have to re-shield the plastic box. (EMI)

If you decide to Modd the ohms on your coils by using a different gauge,spacing or length of coil wire keep in mind that you can exceed the parameters of the TR fets and other components in the logic as well.They are inexpensive but a hassle to replace. A larger heat-sink can help too. Most stock coils are designed to not exceed 50% of the fets capability
drain source on resistance, this is important too, this is the resistance in ohms exhibited across the channel between the drain and the source. this is particularly important in switching applications from logic to power switching and also the same in RF switching.

AzNuggetBob

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Yep, Keep between the Lines.  The Lines our are Friend !   Else the Genie can escape.  LOL

 

Getting a clean measurement from a PI coil is not much of a Issue.  VLF Coils are.  Makers like Whites and Garrett both like to use passive components (Caps and Resistors) within the coil it's self.  A DVM is not going to get you much if anything.   Only option is to get them to Sing with a oscillator set up like above.  Or , do a frequency sweep on them and see where they sing or show resonance.  Some of  Coils are strange birds.  You will find most VLF Rx Coils set up Off Frequency by a Khz or more.   That's how they set up the Phase differential used in the detection , GB and Discrimination circuits.  The TGSL I'm playing with is off set by some 1.6Khz.

Edited by homefire
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I came across some old Discovery Baron Coils to play with.   One was opened so nothing to loose I dissected it.   I now have another coil for one of my Project DIY Pi's .   The Tx coil made with 22 AWG measured come to  .7 Ohms @ 310uH.  Right on the Money for your basic PI Detector.   Why Discovery used this set up as a Tx coil on a VLF is a conundrum  to me at this point.   They must have been putting out a considerably strong  field for a VLF. 

All I need to do is Re apply some Conductive Graphite shielding , foam things,  Some nice white Rattle Can Vinyl Paint   the original enclosure and DONE.  Cool one more for the Toy Box. 

 

Baron ESPcoil -7ohms 310uH.jpg

BaronCoil Housing.jpg

Graphite Shield.jpg

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Latest Project. I have a Kick BUTT Hantek USB oscilloscope but dread digging it out and setting up to have a quick look a something just requiring a single channel. I ordered a DSO 150 Kit. CHEAP ! $21.00 shipped ! Snappy little thing for doing those Peek See things. Some  how trying to put a tracking number on the thing  I doubled my order and received two kits. Guess I have a Back Up Back Up.

If anyone is interested They can be had here:    https://www.banggood.com/Orignal-JYE-Tech-DS0150-15001K-DSO-SHELL-DIY-Digital-Oscilloscope-Kit-With-Housing-p-1093865.html?rmmds=search&cur_warehouse=CN

 

 

1108171725.jpg

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Well, Here I are is. What's Next ?

Waiting for some wire. This is going into a Coil for the TGSL. HOW I ELL can the Chines sell this stuff this cheap, send it half way around the world and still make Money? It would cost me $7.00 just to send this stuff to the next town. https://www.banggood.com/0_2mm100m-...-p-1081668.html?rmmds=search&cur_warehouse=CN

 

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2 hours ago, homefire said:

Well, Here I are is. What's Next ?

Waiting for some wire. This is going into a Coil for the TGSL. HOW I ELL can the Chines sell this stuff this cheap, send it half way around the world and still make Money? It would cost me $7.00 just to send this stuff to the next town. https://www.banggood.com/0_2mm100m-...-p-1081668.html?rmmds=search&cur_warehouse=CN

 

It doesn't cost them anything to ship something that small untill it get on our shores, they just stick it in any nock or cranny of their next freighter headed this way and then their cost with our delivery companies is next to nothing with the volume they give those companies, volume equals BIG discounts on all shipments!

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Yes, that's what I figure.  They negotiated a super bulk and volume  contract.  Probably paying MILLIONS but both take the WIN WIN.   We make up any short fall with the rates we have to pay. 

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This is way over my head...but fascinating. I wouldn't even know what to do with a oscilloscope! Keep it up :worship:

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Not as hard as trying to program that Arduino !  L OL

 

Dave think of them as nothing more then a Volt Meter you can Actually SEE  what the Voltage is doing.  Not only can you see and read the Voltage, you can see what it's doing in relation to Time.  

Edited by homefire
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12 minutes ago, homefire said:

Not as hard as trying to program that Arduino !  L OL

I was waiting for that :ROFL:

You're gonna hate that thing before it's done...if ya don't already!

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