Vlf coil problems!

[jackdetect]

After finished couple of coplanar coils with polyester, they all become far from balance, and useless.

I start trace all component which I use for it with 200M ohm scale, but everything was correct.

After lot of thinking, I was find problem. Black pigment dust which I use to colored polyester (which is usually transparent) was oxide, and that mean probably some metal oxide. When I try about 0,5kg of pigment in plastic can with metal detector, he feel that can from 50cm far.

So, beware with paints for Vlf coils, and do not same mistake like me.

[ivconic]

???


It just happens to know one of people who can solve your problem....He lives a 20 miles away from you. Call him and be polite......
Ha,ha,ha......
Zdravo Zeljko sta se zezas bre!?
Pozdrav....

[jackdetect]

Hi Ivica,

As you see jesterday, I start use white paint for polyester.

I just want to warn others, becouse lot of paints makes from oxid pigment, and that mean, can afect on balance quality.



Pozdrav druze, i sledeci put kad dolazis, ponesi tog gareta da ga testiramo na poligonu!

[J_Player]

Hi all,
I have long time experience with painting and first hand experience with paint chemists. I can tell you something about paint and pigments: The pigments that are used in paints are made from ground up rocks and minerals. These pigmensta are powdered minerals that have the colors needed for the final paint color. The purpose of the pigments is for asthetic coloring as well as UV protection to block the sun from eating the resins that make up the paint. When it comes to painting metal detector search coils, this is what you need to know:

Most white pigment is made from titanium dioxide. Most brown pigments contain one of several forms of iron oxides (rust) ground up into a powder. There are a number of other pigments that will change the electrical values of your search coil to make your detector un-usable. Most cheap paints contain a large amount of clay to act as a pigment to provide opacity. These clays are usually mineralized. If you want to use a paint on your coil withhout adverse electrical effects, then here is what you should do:

1. For a water based coating, go to Home Depot and buy Behr deep tinting base. This is cutting edge acrylic resin paint with NO pigments added. DO NOT use pastel base or medium base. These paint bases contain titanium dioxide pigments. You want to buy unpigmented paint base, with NO pigments except your own pigments which you can control. If you want to add pigments, I would suggest adding graphite powder for a controlled resistivity coating. Make sure you know what you are doing before adding any pigments to your mix -- see this thread for reasons why you might want to add graphite to an unpigmented base: http://thunting.com/geotech/forums/s...ht=resistivity

2. Oil based paints work the same as water based, except they are a little more brittle when they are dry.

3. Beware of exterior clear deck and siding sealers. These products usually contain a small amount of amber colored pigment to help with he UV shielding. The manufacturer almost NEVER tells you that there are added pigments. And these pigments usually contain iron oxides which will have very noticable effects on a search coil.

Your best bet is to buy the highest quality deep tinting base you can find. Top quality is Behr, Benjamin Moore, Pratt and Lambert, Pittsburg and Evr-Guard. These are all approximately the same top quality, cuttng edge resins manufactured by Rohm and Haas. Forget about Dunn-Edwards, Glidden and others that use resins from the Pacific rim.

My preference is the water-based acrylic resins. You can buy a gallon of Behr deep tinting base for less than a tank of gas, and it is cutting edge technology. It won't crack when your coil flexes, and it dries in 1/2 hour, with water clean-up for spills. Use it straight from the can, or add whatever pigments you want. Hint: you only need a quart.

A better choice is epoxy. A high quality epoxy will dry slightly flexible and have no trace of porosity to let water migrate into the wires of your coil. A favorite choice is Gougeon Brothers West System epoxy (manufactured by Safety-Poxy in Torrance, California). You can get a 6-pack of envelopes of this top quality epoxy here: http://www.jamestowndistributors.com...em.Epoxy.Resin (also available at any WestMarine store in your locality).

The kit costs $25, and it will take 1 or 2 of the 6 packs to do a single coil.

I have used the all of the products listed above and found them to be the best available for paintng and epoxy applications. I have not used any of these products on a coil. I only speculate they will be top performers on a detector search coil based on my knowledge of the characteristics of these products. If I were building a search coil, I would go to the local WestMarine store and buy a 6-pack of epoxy repair kit for $25 and use this to seal my coil.

If you have no WestMarine or Home Depot in your area, then look for the best epoxy or Clear paint without pigment that you can find. Good luck with your coils.

[Geo]

Fine

Hi J_Player.
Congratulation. Your article was very instructive and specialised.

[Mike]

Excellent

Thanks J Player - very useful information.

[jackdetect]

Hi J Player, thanks for the info.

I was also use lot of pigment paints for my art paintings, but never think about their chemistry. Only knows that exist oxide and organic dusts.

I was made tons of smaller coils with polyester kit.

I had not intention to start some academic debate about paints, only want to share my bad experience with colleagues, to prevent similar mistakes.

But, we can expand discussion about it.

Polyester kit is good and cheap solution for small coils. But he is very heavy because usually mixed with chalk. Better is kit with fiber, but he is usually gruff.

So, for bigger coils better is to use pure polyester because of weigh. But such polyester need to paint with something, therefore hi is transparent.

I was never try to colored something with graphite dust, and know nothing about his colored possibilities. But, There is some technology if want to use graphite for electrostatic shield. If you simply put graphite in polyester, he will not have electrical conductivity, so it will not work like shield. Is some technology for make graphite conducting paints, but I never can find details.

Fisher in his spider coils in down layer use some electrical conducting polyester mix with graphite. You can measure resistance of it with ohm meter. I will like to hear from you how to make such mix. What we need to put in polyester altogether with graphite dust, to become conducting?

For paints, only need to put it in plastic bin (usually sell in metal cans), and try it with MD, if affect MD, don’t use it for coils.

[J_Player]

Hi Jackdetect,

The reason I talk about paint pigments is because the pigments in paint can cause a bad change in how your search coil works. This is the same problem you found when adding pigments to your polyester kit.

What I am saying is you may use ployester, or epoxy, or paint, as long as there is no pigment added. This means clear color paint or resins. Only clear will work. When you add pigments, you must be certain these pigments have no electrical properties that will change your search coil.

The talk about graphite came from another forum topic where people were asking how to mix graphite into resin or paint to make a coating like Fisher coils use. This is only an experimental idea to mix and make tests until the method is perfected. You can read the details here: http://thunting.com/geotech/forums/s...ht=resistivity

[jackdetect]

I was try to understand ideas in that topic, but my limited English, and lot of unknown components makes to not understand. It is not relevant, because I newer appreciate much graphite shield and always use foils for shielding.

My interest for graphite conducting paints was only about electroforming.

But, conducting paints can provoke different problems. In the beginning of my MD coil experiments, once, I was use paste (glue for wood) to fix coils and wires, and get total out of balance. Find that wood glue have conducting property when his wet. But after couple of days, when dry, everything becomes normal. I was notice that lacquer wire not quite isolated, and some conducting materials can provoke unwanted current flow. So, need to be careful with using conducting paints. Probably best way is to put some isolation layer between wire and conducting graphite paints.

[ivconic]

Opet Ja


"After finished couple of coplanar coils with polyester, they all become far from
balance, and useless..."
How about balancing it after assembling...There are ways to do it after.Besides,
proper calculation of coils are leaving you comfort to "distort" balance a bit with
housing assembly and later to compensate with the rest of electronics.
It is funny but the shielding is a sort of "distortion" too !
Only a mismatch in coil calculation can "distort" a balance in a huge percent.
About faraday shield....A small tip...I am using a electrostatic "plastic" bags for
it. Those bags you can find when buy some hard disk or mother board for pc.They are
usually packed in it. When opened first time a Scorcher coil for Garrett GTI 2500,
i founded exact same material used as shield in it! Simply cut in the round shape
and glue it on the housing, after that try somehow to connect it with gnd. There are
many ways to do that..But i guess, you already know how. I have been seen your
detector - your own design, and i liked it. It is working just fine. You may
compare it with a better comercial models with no shame at all.Keep it that way!
But making a coil, sometimes is a real pain in the.....That's why I prefer more
a DD coil than coplanar's. Although i made a few very good of those.What i am really
ineterested about are Minelab DD coils..The very best ever !!!
That's all for now. Regards.

Garet je na sluzbenom putu i ostace duze, ali planiram da donesem Pulsestar sa
sobom sledeci put i testiram ga na tvom poligonu.Mada sam ga testirao "milion"
puta i vec znam rezultate, ipak zeleo bih da i ti vidis svojim ocima....
Usput,evo,moj brat Quiaozhi je poslao spisak zamena za op.amp-ove 2082,2081...
i slicne. Mozes pogledati na ovome forumu, na thread-u Accumeter VI, tema
Geophysics...
Pozdrav tebi Zeljko i tvojoj porodici a narocito tvojoj koleginici !!!
Cujemo se, vidimo se...

[jackdetect]

You are right about everything, except about Minelab DD coils. I was very disappointed with all Minelab models after real field tests. Advertising papers gives quite different picture then real possibilities.

To deal with all coil parameters, and get useful product is real art, and need years of experience. Also, to get coils with equal quality need much more working hours, then manufacturers usually wish to spend on it.

Pozdrav!

p.s. Ako Marijin decko pronadje tvoje pozdrave, ne bih voleo da sam u tvojoj kozi!

[ivconic]

???


Dear Jackdetect, real "field" test tells you nothing!!! Real, and i mean REAL test is on the REAL terrain, outdor in the wood or forest on some location, not in your backyard. And the real REAL results of MInelab DD coils are excell !!!
ANd i am ready to make any bet on it. We can compare any other coil and any other convetional vlf i/b detector with Minelab Excalibur or Relic Hawk to test it on the REAL field. My experience dated since 1987. During those years (i never told you that until now) i was tested over 50-60 detectors with diff. coils under diff. conditions and i do consider myself very competent to claim such claims.
Me, myself, I own a several detectors like Garrett GTI2500,PulsestarII,CSCOPE1220B,White's Classic III and a few handmade's.But unfortunatelly i do not own any Minelab yet(which i intend to buy a.s.a.p).But still i worked on the field with few Minelab's,one of Relic Hawk's i saw in your lab,as you maybe remember,and i liked it.So trust me,to judge about detectors you just do not have to be excell constructor like yourself, but you have to visit more REAL conditions either.
So i can salute to you to your constructor's abillities and your nice designs,but i really can not respect your minor knoledge about "real life".
About coils....well coils are pure maths,nothing else.Trust me on this,i made over 200-300 coils so far.Every of them are working perfect!Pure maths, nothing else.No mithology,no abracadabra at all!
That's all for now.Best regards and you just leave your lab and go outdor more often, at least you catch some fresh air, if nothing else!

About M. No hard feelings! It was just regard, nothing else!
again best regards!

[Mike]

Electrostatic Bag Screen

About faraday shield....A small tip...I am using a electrostatic "plastic" bags for it. Those bags you can find when buy some hard disk or mother board for pc. They are usually packed in it.

That's interesting. I have very little experience with coil building, but I asked about the use of electrostatic materials for sheilding (http://thunting.com/geotech/forums/showthread.php4?t=1141 The view there was that the conductivity (100000 and greater) was probably too high.

When opened first time a Scorcher coil for Garrett GTI 2500,
i founded exact same material used as shield in it!.

If Garrett are using such high resistivity screens, it must be effective I guess. Handling this electrostatic sheeting is easier that dealing with electrostatic paints, at least for the beginner (like me). But looking in the Farnell catalogue (e.g. item 522-78, the downside is that the cost is probably higher if you have to buy these bags new.

Thanks for the information - even more options

[Qiaozhi]

Electrostatic Shield

Originally Posted by ivconic
When opened first time a Scorcher coil for Garrett GTI 2500,
i founded exact same material used as shield in it!.

I have also found this electrostatic sheet in a Garrett GTAX1000 coil. The connection to the shield is made via a steel spring which presses against the sheet when the two halves of the coil shell are combined.

[Geo]

[/i]
The connection to the shield is made via a steel spring which presses against the sheet when the two halves of the coil shell are combined.

Simple and clever method