Crude coil sheilding paint

[Tinkerer]

The most important factor with a shield, is a solid high conductive connection to the drain wire.
Using carbon composition material, like the old-time carbon composition resistors, and using the same technique to bind the carbon composition to the wire, worked well for me.

I have posted a recipe several times already, if I could only find the post.

Tinkerer

[turtlebowl]

Kev, have you any powder to paint ratios jotted down and their respective resistance Opis to use as a guide? What paint base did you settle on and are you spraying or brushing?
I tryed some stuff with rubber cement last night and was dissapointed. To gooie, even diluted.
I like Mikle's post about the elmers becuase it is so easy but I wonder about anything water based that is used outdoors becuase of condensation??
Anyone have any knowledge or thoughts on condensation VS water based sheilding? Maybe there wouldn't be condensation if both inside and outside temp of enclosure were equal?
I'm going to the hardware store for graphite and screw around some more with this. I am looking for Opis about 600- 1K.
Phil M

[Kev]

Hi Folks,
Minelab use graphite, which is a very lossy material, whereas carbon black has very little permittivity and next to no effect on field transmission. I'm trying to make my coils more sensitive and quieter than those commercially available.

I got the carbon black paint to work, but I'm now moving towards flattened litz wire wrapping with strands of human hair thickness. I visualise it like trying to catch fish in a canvas bag as opposed to a fine net, the conductive paint is like the bag and the wire wrap like a fine net, if you get my drift, soon I'll know if I'm blind or not.

From what I've experienced in the field, coil performance is one of the most important factors affecting how much gold, with respect to size and depth you will find in a day.

HH
Kev.

[turtlebowl]

Simon, the Scotchkote is called liquid tape. A fancy name for rubber cement I believe. Another branded name is : Performix electrical liquid tape.
From what I gather it is used on electrical connections as an insulator. The acetone of course is just a thinner.
I believe if you follow my link above it brings one to this info. Then follow that guys link for other formulas and products.
Phil M

[Vortxrex]

How are basic resistors made? I am thinking they are epoxy mixed w/graphite in varying concentrations depending on the value.... Maybe we should call this "resistor paint"

[simonbaker]

Can't we use any good quality paint (that will stick to the coil shell or coil covering) and add the same ratio of graphite powder?

Good question to answer with experiments.

I am still perplexed as to how graphite creates a conductive path when it is immersed in insulating goo -- I would think that each particle, or clump of particles, would be insulated from its neighbors. But I guess it works somehow.

-SB

[maikl]

Cheapest possible binder in # 161 http://www.geotech1.com/forums/showt...t=17396&page=7

[Vortxrex]

Can't we use any good quality paint (that will stick to the coil shell or coil covering) and add the same ratio of graphite powder?

[simonbaker]

Here is a great idea from our luthier friends. Produces a paintable approx 100 OHM shield. The link in the article has several other formulia.
DIY Conductive Paint for Cavity Shielding

http://www.talkbass.com/forum/f38/diy-conductive-paint-cavity-shielding-589012/

The formula I used was one part 3M Scotchkote Liquid Tape, 1.5 parts graphite powder, and 1 part Acetone. I created the mixture in small batches, just enough for one coat since the solution starts to setup in about 10 minutes. The solution was painted on in three coats using disposable acid brushes allowing 20 minutes between applications.
Note that the spacing on that Precision Bass is approx 6 inches and 3 coats. Wonder what 1 coat and 1 inch would be?
Phil

Looks promising. I couldn't find anything called exactly "3M Scotchkote Liquid Tape", is there another name? Also, it would be good to find the cheapest binder possible.

-SB

[turtlebowl]

yet another concoction

Here is a great idea from our luthier friends. Produces a paintable approx 100 OHM shield. The link in the article has several other formulia.
DIY Conductive Paint for Cavity Shielding

http://www.talkbass.com/forum/f38/diy-conductive-paint-cavity-shielding-589012/

The formula I used was one part 3M Scotchkote Liquid Tape, 1.5 parts graphite powder, and 1 part Acetone. I created the mixture in small batches, just enough for one coat since the solution starts to setup in about 10 minutes. The solution was painted on in three coats using disposable acid brushes allowing 20 minutes between applications.
Note that the spacing on that Precision Bass is approx 6 inches and 3 coats. Wonder what 1 coat and 1 inch would be?
Phil

[moodz]

.... you could just type this number into ebay 130474942236

$7 for 350 gram of chemically pure graphite powder.

[simonbaker]

Great thread! I have read all the posts in this thread but to busy/lazy to search the forum relating to this great topic.
Has anyone tryed pulverising pencil lead for graphite? I did some quick tests this morning after reading this thread.
Different pencil manufacturers lead produce different readings. Relative to lead diameter I think. Perhaps composition as well? I tryed three different manufacturers.
Anyways I am curious to know this. Using the same compound will a 1/16" round straight pencil lead have the same resistance as a broad solidly filled in circle? I ask this becuase my measurements this morning were simple test leads on opposing ends of the pencil lead.
Resistance was only about 10 ohms per inch. Then it occured to me that maybe if the graphite field (as in sprayed on) were broader and much thinner the resistance would be higher? Would seem so.
So has this idea already been disscussed elsewhere?
Phil

I once tried rubbing a soft pencil on rough paper to make as thick a layer as I could, then measured resistance. I don't remember actual resistance, but I believe it was something like 1K per inch maybe. That would still discharge static electricity probably -- whether that would be useful depends on how shields are supposed to work.

Since then I acquired a bottle of graphite as well as a spray can, but have yet to test it out. It's probably not simple to prove a shield is good -- you need to find a situation where it is needed (wet grass? certain soil? certain noise environment?) and compare to another shield.


-SB

[Kev]

Hi turtlebowl,
Yep, graphite powder has been used by some, and Minelab had traditionally used this on cardboard for shields, it's like a thick coating of pencil lead, and measures about 45 to 100 ohms. I imagine a thicker lead will have less resistance.

I've just put the forth ground carbon rod into my small pottle of paint (50 mils) but I'm still only getting 200 Ohms, I need to get it down to 100 Max for my GPX. A coil for a non-fussy PI such as a Hammerhead, would be happy with a shield of 1 or 2k Ohms.

PLEASE NOTE: I got big sparks from my Dremel last night while grinding down carbon battery rods. Some of the dust must've been sucked in and built up around the mains input. Please be careful if you do this. I am now going to insert the Dremel head into a container and grind the rod inside of it so that the carbon dust will not be floating around everywhere.

Be Safe
Kev.

[golfnut]

you could use a foil quiche tray

[turtlebowl]

Great thread! I have read all the posts in this thread but to busy/lazy to search the forum relating to this great topic.
Has anyone tryed pulverising pencil lead for graphite? I did some quick tests this morning after reading this thread.
Different pencil manufacturers lead produce different readings. Relative to lead diameter I think. Perhaps composition as well? I tryed three different manufacturers.
Anyways I am curious to know this. Using the same compound will a 1/16" round straight pencil lead have the same resistance as a broad solidly filled in circle? I ask this becuase my measurements this morning were simple test leads on opposing ends of the pencil lead.
Resistance was only about 10 ohms per inch. Then it occured to me that maybe if the graphite field (as in sprayed on) were broader and much thinner the resistance would be higher? Would seem so.
So has this idea already been disscussed elsewhere?
Phil