Question - I purchased some raw nickel flake for shielding

[Charles (Upstate NY USA)]

At $25 a can the nickel EMI spray paint was getting expensive, those 12oz cans don't last long so I just purchased 4 pounds of raw conductive nickel flake. I wonder if anyone has tried to mix this with the casting resin and what ratio they used to yield a given resistance?

I'm thinking about a few different options, I could lay down a thin coat of resin, then just when its tacky I could power coat the coil shell, or I could mold the RX coil in a resin/nickel mix then place in the shell and seal with pure resin, or I could just mix a bunch of this in with the resin and pour it all at once but I'm thinking that might get too heavy.

[Robby_H]

Re: Question - I purchased some raw nickel flake for shielding

I'm afraid I'm not much help but I would like to know what non-insulating resin or paint you use. I had a brief play with graphite and a water based laquer and also tried a water based glue with mixed success and it appears that the mix needs to contract slightly when drying for better particle contact.
I might be reading you wrong but the shield should provide a fixed, slight capacitive coupling uniformly between the two coils in a way so as to over-ride the varying capacitive influence of the ground, shielding just the rx coil wouldn't give any real benifit.
Rob.

[Charles (Upstate NY USA)]

Its called Supershield...

There is a brand of nickel based EMI shielding paint out there called supersheild. If sprayed on medium thick you can get 1-4 ohms resistance per inch, the problem I'm having with spraying the shell is occasionally I get a thin spot thats not shielded enough and wet grass will cause some falsing, plus the spray doesn't go far and its $25 a can.

They also offer it in a brush on can which I may try next. I'm thinking premold the coils with just enough material to build up some space between the coil shield, then place in the shell and pour.

The nickel powder mixed with resin did not work, it wets out and you lose conductivity, though I also tried a test where I sprayed a test strip with spray paint, then powder coated the spot and that worked pretty well so some variation of that might work.

Tech note...nickel (either powder or spray paint) reacts chemically with urethane resin creating a zillion bubbles so it must be sealed from the resin.

[Reg]

Re: Its called Supershield...

Hi Charles,

You might try some semi-conductive rubber tape to see if it works on your coils. 3M makes some that sells for about $10 a roll. It is normally used on high voltage connections to eliminate corona arcing.

I tried it a while back on a mono coil and it seemed to eliminate the ground capacitance problem, but didn't work that well for reduction of noise on my PI.

Unfortunately, it is quite thick so there has to be some room inside the housing for it.

Also, if you haven't visited the website linked below, you might see if they have something else to try. They have about the largest selection of other types of materials I have found that might be used for shielding.

Reg



LESSEMF

[Charles (Upstate NY USA)]

Thanks Reg...

I purchased 4 cans of Supershield from them a couple weeks back. One blew out in my face by the way, the nozzle clogged and so I thought I'd just pull it off and use one from an empty can, as soon as I removed the nozzle about half a can blew out all over me, ugh!

Anyway they have some other products with potential, I might try some cobalt tape but thats pretty expensive. Tonight I have been working on creating my own conductive fabric tape by mixing the raw nickel powder with various paints. Water based urethane, the kind for wood floors is conductive. The question is can I wrap the coil without the stuff flaking off or cracking.

Another option I'm thinking about is coating the coils with Plastic Dip spray paint which remains very flexible, then slopping on some conductive mix, or using the Supershield spray, if I only have to coat the coils and not the entire shell that may save enough material to make the spray cost effective.

[Sean Goddard]

Re: Question - I purchased some raw nickel flake for shielding

Charles, I'm STILL interested in importing this thing into the UK.

Alternatively, can you make custom vacuum mouldings cheap enough for me?

You have my email addy from the last time you contacted me.