Opened my tesoro widescan coil

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"In Dons document about shielding he masked off a line down the radius of the housing in order to stop eddy currents in the shield. I just did it anyway even though he found no difference with it and without it on his designs?he also said it was best practice." Quote from here:

http://www.adrianandgenese.com/blogger/2016/07/18/diy-metal-detector-coil-housing-build/

[cristiano.sar]

understood. the gap perhaps needed if the layer has very low resistance, Ohms. without the gap the layer is like a short-circuited loop
for EMF (because TX power is EMF itself, the nature). you maybe want to reduce losses. has some sense. but if you do (right do) high resistance layer
you sure do not need doing the gap.
a case with discs, NO gap between discs. be cause high impedance graphite layer.
that was first way to protect in history - they use a paper with graph layer. later they use graph covering inside the housing,
Garret uses a special plastic with conductor for wire bobbins, like a mix. so you do not see a graph layer in Garrett coil but the ESFI protection is.

Thanks for the perfect explanation.

[kt315]

understood. the gap perhaps needed if the layer has very low resistance, Ohms. without the gap the layer is like a short-circuited loop
for EMF (because TX power is EMF itself, the nature). you maybe want to reduce losses. has some sense. but if you do (right do) high resistance layer
you sure do not need doing the gap.
a case with discs, NO gap between discs. be cause high impedance graphite layer.
that was first way to protect in history - they use a paper with graph layer. later they use graph covering inside the housing,
Garret uses a special plastic with conductor for wire bobbins, like a mix. so you do not see a graph layer in Garrett coil but the ESFI protection is.

[Stevedbk]

My Minelab FT16000 has 2 flat impregnated paper disc shields. One above the double d and one under it. They are joined by a single flexible wire. The gap is in between the discs.
Maybe yours is the same.
Steve

[cristiano.sar]

ML uses especial strip connected to preamplifier, on its input. or, you can show by pic your coil, your coil without the pre amp?

In this case I'm asking about the dfbowers coil casing having a strip (line) not painted with graphite. If having this not painted line is really needed (maybe because is coil is a concentric?), because I can't see something like that in Minelab commander coils (DD) shielding, like in the images below:

dfbowers casing (have a not painted strip / line):


minelab commander (full painted):


Thanks.

[kt315]

... for example

[kt315]

Nice coil.
One doubt, the strip that is not painted is really needed? Even if I use a DD coil? I'm asking that because I can't see that strip for example in a Minelab commander DD coil.
Thanks.

ML uses especial strip connected to preamplifier, on its input. or, you can show by pic your coil, your coil without the pre amp?

[sinclairuser]

tv tube shielding paint works too, its a lot like guitar paint but its thicker and comes in two forms a dry powder you can mix with solvent or water, or ready mixed.

[cristiano.sar]

I purchase "guitar shielding paint" from ebay.
It's a water-based carbon paint that is cheap and very conductive. It's also thick enough to attach wires to the paint.

Nice coil.
One doubt, the strip that is not painted is really needed? Even if I use a DD coil? I'm asking that because I can't see that strip for example in a Minelab commander DD coil.
Thanks.

[kt315]

do not run for low resistance of the carbon layer. you have to get only some ability to discharge of accumulating surface charges sufficiently fast.
also, measuring of the resistance is not correct be cause acting voltage reaches a value in 10000+ V (10kV +) while you use a tester with just 9V battery.

.

[dfbowers]

I purchase "guitar shielding paint" from ebay.
It's a water-based carbon paint that is cheap and very conductive. It's also thick enough to attach wires to the paint.

[cristiano.sar]

I made my own graphite paint.
Used powered graphite mixed into clear polyurethane wood finish. I did a number of different paint products with different amounts of graphite powder.
Painted onto a piece of cardboard and choose the one that gave a consistent resistance measurement. I think it was about 1-5kOhm at 1 cm with DMM probes.

Used this on the DD coils for a TGSL. Each coil wound then wrapped with electrical tape. A very fine wire then spiral wrapped on each coil and not connected as a loop.
Painted over with the graphite mixture. After drying wrapped with another layer of electrical tape. This keeps the shield lay on each coil from touching. The thin 'drain' wire then connects to the coil cable to the TGSL's ground.

I have read that Guitar shield paint works well but it is pricey.

Thanks! I will try that mix.

[waltr]

One doubt about graphite shielding, when making our own graphite shielding, do you recommend using commercial graphite paints or making your own?
If making your own, do you have some tutorial of it?
Thanks.

I made my own graphite paint.
Used powered graphite mixed into clear polyurethane wood finish. I did a number of different paint products with different amounts of graphite powder.
Painted onto a piece of cardboard and choose the one that gave a consistent resistance measurement. I think it was about 1-5kOhm at 1 cm with DMM probes.

Used this on the DD coils for a TGSL. Each coil wound then wrapped with electrical tape. A very fine wire then spiral wrapped on each coil and not connected as a loop.
Painted over with the graphite mixture. After drying wrapped with another layer of electrical tape. This keeps the shield lay on each coil from touching. The thin 'drain' wire then connects to the coil cable to the TGSL's ground.

I have read that Guitar shield paint works well but it is pricey.

[kt315]

welcome!

[cristiano.sar]

my english does not give me possibility to do tutorials. i write here. yes, i use graphite aerosol but with adding of graphite powder.
this way gives significal economy because the balloon price is expensive (for me). instead 2-3 layers i put just one.
also one layer is cracking after drying.
if you do your own, seek solver powder or make the powder from silver. add it in graphite.

Thank you so much!