Graphite coil shielding for TGSL problems

[billr]

Thanks for that Goaty.
Will look at it as soon as I post this.

Hi George.
Do you think this would be a good baseline to start with for the TGSL?
60 Ohms would be a really thin coat but I think its possible with a cotton swab to get a more even coverage at such a low value.
Alternatively I could try this spray for a more controllable outcome.

https://uk.farnell.com/kontakt-chemi...00ml/dp/832959

[surfdetector]

To get higher resistance value in the coating up to 10K the only way I know how to do that is by ADDING more paint making it thicker.
Thinner paint would be less over all and equal less resistance. Would it not?
Unless I am missing something. You cant have it both ways.

As graphite is a conductive material, the more graphite that is added = the more conductive material that is present and hence the lower the resistivity on the region of the coating.

[Qiaozhi]

I've just taken a resistance reading on the graphite coating in a White's Eclipse coil shell, and it measures around 60 ohms with the probes 1 inch apart.

[Goaty]

I hope this is not too far off topic but I recently found this video on making a quite professional conductive paint and also shows how to measure square conductivity.

https://www.youtube.com/watch?v=zyGX-VyXXTQ

Lots of other info on graphene as well which may prove interesting for experimenting with shielding materials.

[billr]

billr

The sheet resistance is to low. It should be tens of thousands of ohms (1 to 5) at least to avoid signal lose. Need thinner paint. If you can't reach 10K or more at least shoot for a few K ohms.

Adding more paint make your problem even worse.

Is anyone else confused by this comment or is it just me?
Low ohms to me, means 5R, 10R as in a low ohm resisters.
High ohms would mean 10K upwards.
To get higher resistance value in the coating up to 10K the only way I know how to do that is by ADDING more paint making it thicker.
Thinner paint would be less over all and equal less resistance. Would it not?
Unless I am missing something. You cant have it both ways.

[rickb]

Really?
Well I guess I could add more coats and try in between each coat to see how it goes.

Adding more paint make your problem even worse.

Maybe you're a troll, maybe not. In any case I'm done.

[6666]

https://en.wikipedia.org/wiki/Triboelectric_effect

I have to try that on our cat.

[waltr]

Waltr.

Triboelectricity is a different issue. It relates to conductor movement inside a cable. It can be a problem with coil cables, but that's not the issue here, and shielding won't fix it.

https://en.wikipedia.org/wiki/Triboelectric_effect

[billr]

Really?
Well I guess I could add more coats and try in between each coat to see how it goes.
Think I will use some release agent I have for fiberglassing on the shell before I start. It's none conductive and water soluble. Removing cured graphite is a PITA even with acetone. MEK would do it real fast but prolly dissolve the plastic.

Keep ya posted on my findings.

[rickb]

billr

The sheet resistance is to low. It should be tens of thousands of ohms (1 to 5) at least to avoid signal lose. Need thinner paint. If you can't reach 10K or more at least shoot for a few K ohms.

[billr]

[ATTACH]54375[/ATTACH]


are you sure you haven't got a ground loop problem


I had a coil that you could just gently blow over the top and it would chatter away


I would temporarily jumper from the shield to Rx ground on the PCB and not connect the shield in the head

What the heck. Anythings worth a try. Thank you. Will give it a go tomorrow.

[billr]

Last: I can be Very difficult to evaluate inside a house, workshop, due to AC Mains EMI and EMI from many, many appliances, etc in and around the house. The EMI can cause the 'Morse code' sound (that sound like some piece of electronic/electric equipment in your house and when it sound is not there that piece of equipment is not emitting EMI. Been there trying to get my first detector working.
If the shield prevents this then it will also decease detection distance.

Thank you Waltr.
As always. Great info for leaning.
Yes I recall recently I posted some issue with another machine. PI having coil noise and it turned out to be underfloor piping or cables so I learnt from that to do all testing outside away from power cables etc.

Hmmm. I wonder if I have over or under shielded and its causing a conflict with itself being able to null silently? It's like it is fighting any correction made to it, resulting in the Morse code effect.
Just me thinking out load.

[Koala]

are you sure you haven't got a ground loop problem


I had a coil that you could just gently blow over the top and it would chatter away


I would temporarily jumper from the shield to Rx ground on the PCB and not connect the shield in the head

[billr]

What is the sheet resistance of the shell shielding? measure from opposite edges for very rough approximation. Did you thin the paint and test each layer before adding more? Are you using the paper shields and shell shields at the same time? You only need one type.

Its a DD shell so measured from 12 o'clock to 6 o'clock at the widest section between 1500 and 2000 ohms. Brush painting isn't very constant.
From 9 to 3 o'clock roughly 200 ohms. That part is only wide enough for the coil plus a little space either side as you know.

Yes, I thinned to very water like consistency (dried fast after application). Only applied one coat to shell but could see a decrease in range and increase in noise suppression.

At first I cleaned the shell of any paint applied preciously and used paper shields to gauge how much paint to apply to shell. When using different thicknesses of paint on paper my results showed noise reduction and range.

After painting the shell with one coat I did try placing the thinnest coated paper on top to see what happens. Same as above unfortunately.

[rickb]

Waltr.

Triboelectricity is a different issue. It relates to conductor movement inside a cable. It can be a problem with coil cables, but that's not the issue here, and shielding won't fix it.