Charcoal for coil shielding material

[6666]

I have found some conductive fabric tape that works extremely well and is very reasonably priced in various widths. It is item 262159780594 on ebay. Wrap around coil but leave a gap to prevent shorted turn and connect with a drain wire under the adhesive. I used a 15cm length of 7/0.2 stranded pvc insulated wire with 75mm stripped, splayed out slightly and under the start (or end) of the shielding layer. The connection from the drain wire to the tape surface measured 0.1 ohms, which is good. To the far end of the shield at the gap it measured 0.5 ohms to the drain wire.

Eric.

Hi Eric thanks for the tip, FOUND IT BY SEARCHING THROUGH GOOGLE.

[eclipse]

http://www.ebay.co.uk/itm/UK-20M-Con...-/262159780594

[6666]

http://www.ebay.co.uk/itm/UK-20M-Con...-/262159780594

Thanks but they only post to the UK, I found some on the .au ebay and ordered some.

[Qiaozhi]

I have found some conductive fabric tape that works extremely well and is very reasonably priced in various widths. It is item 262159780594 on ebay. Wrap around coil but leave a gap to prevent shorted turn and connect with a drain wire under the adhesive. I used a 15cm length of 7/0.2 stranded pvc insulated wire with 75mm stripped, splayed out slightly and under the start (or end) of the shielding layer. The connection from the drain wire to the tape surface measured 0.1 ohms, which is good. To the far end of the shield at the gap it measured 0.5 ohms to the drain wire.

Eric.

I'm going to order some, but which tape width would you recommend?
Also, did you overlap the tape, position each loop side by side, or leave a gap between each loop?

[Ferric Toes]

I have bought both 25mm and 30mm widths. I depends on the bundle diameter but if possible I do not spiral wrap the shielding as it is very tedious, especially on small diameter coils. I cut a length about equal to the coil circumference and do a fold over job around the coil winding. First though I put on some spiral wrap as a spacer to reduce the coil /shield capacitance. Below are some pictures of the process. The 30mm width tape just overlaps on the coil, whereas the 25mm is right for coils with thinner wire e.g. the Vallon detector. A wrap with pvc tape prevents the resin in the potting process from softening the shielding tape adhesive. It is only a precaution, but did happen with some previous tape some years ago. Don't forget the gap in the shield which is best where the wires come out.

Eric.

[Qiaozhi]

I have bought both 25mm and 30mm widths. I depends on the bundle diameter but if possible I do not spiral wrap the shielding as it is very tedious, especially on small diameter coils. I cut a length about equal to the coil circumference and do a fold over job around the coil winding. First though I put on some spiral wrap as a spacer to reduce the coil /shield capacitance. Below are some pictures of the process. The 30mm width tape just overlaps on the coil, whereas the 25mm is right for coils with thinner wire e.g. the Vallon detector. A wrap with pvc tape prevents the resin in the potting process from softening the shielding tape adhesive. It is only a precaution, but did happen with some previous tape some years ago. Don't forget the gap in the shield which is best where the wires come out.

Eric.

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Thanks Eric.
I've ordered a 30mm reel.

[jladre]

What I was trying to ask was did you actually use charcoal or something else, not the glue.

Yes i used wood charcoal. Wood charcoal resistance depends on the kinds of wood.. the process i did is similar unti this https://youtu.be/W_ouYLeIkoo.

[eclipse]

There's super expensive Teflon tape being sold now on ebay for 1/5th of the regular price (39GBP vs - 232 EURO) for 100ft role (30m) with expired date but probably still good to use. http://www.ebay.co.uk/itm/TE-Connect...53.m1438.l2649

[6666]

Hmmm, Ive just received my 5mm conductive tape, I bought 5 mm thinking that it would be easy to spiral wrap the coil, the tape i bought has a plastic backing that has to be peeled off , so spiral wrapping could be tricky.

Quick test shows about .4 ohms for about 100mm length of 5mm wide.

[ionut_mtb]

I have found some conductive fabric tape that works extremely well and is very reasonably priced in various widths. It is item 262159780594 on ebay. Wrap around coil but leave a gap to prevent shorted turn and connect with a drain wire under the adhesive. I used a 15cm length of 7/0.2 stranded pvc insulated wire with 75mm stripped, splayed out slightly and under the start (or end) of the shielding layer. The connection from the drain wire to the tape surface measured 0.1 ohms, which is good. To the far end of the shield at the gap it measured 0.5 ohms to the drain wire.

Eric.

How low delay can go with this shield? your spiral wrap is pe? Did you ever tried carbon fiber as shield and actual case for a coil? thanks

[ionut_mtb]

There's super expensive Teflon tape being sold now on ebay for 1/5th of the regular price (39GBP vs - 232 EURO) for 100ft role (30m) with expired date but probably still good to use. http://www.ebay.co.uk/itm/TE-Connect...53.m1438.l2649

i'm not sure it is teflon...

[mohalothman]

i think that the aim of the coil shielding is eliminating effect due to electrostatic field which means that the shielding material don't have to be very conductive
for PI coil i did a rough estimation of a proper resistor range of the shield that will not affect the preamp output decay
i brought a 30cm copper wire its thickness was about 2 mm i formed it in circular shape but it is still open loop and insensible to PI machine
then i closed the wire loop with a different value resistors i concluded the PI machine would sense the loop with a resistor less than 1 ohm therefore a shielding sheet with let's say 100 ohm/square is just fine.
for the shielding issue i made a DIY conductive ink contain ultrafine graphite powder mixed with oil-based paint i tested the ink on paper after the ink dried i got a 200 ohm/square resistance. finally i taped a thin cooper wire to inner surface coil house and painted over the wire all the inner surfaces. the result was very good better than aluminum foil in fact the aluminum foil was not a good choice because my coil is spiral one so it has wide surface.

[ionut_mtb]

i think that the aim of the coil shielding is eliminating effect due to electrostatic field which means that the shielding material don't have to be very conductive
for PI coil i did a rough estimation of a proper resistor range of the shield that will not affect the preamp output decay
i brought a 30cm copper wire its thickness was about 2 mm i formed it in circular shape but it is still open loop and insensible to PI machine
then i closed the wire loop with a different value resistors i concluded the PI machine would sense the loop with a resistor less than 1 ohm therefore a shielding sheet with let's say 100 ohm/square is just fine.
for the shielding issue i made a DIY conductive ink contain ultrafine graphite powder mixed with oil-based paint i tested the ink on paper after the ink dried i got a 200 ohm/square resistance. finally i taped a thin cooper wire to inner surface coil house and painted over the wire all the inner surfaces. the result was very good better than aluminum foil in fact the aluminum foil was not a good choice because my coil is spiral one so it has wide surface.

regarding your test, it depends how low you want the delay to be, for under 10us is possible that the wire itself (2mmdiam) can be detectable. 'am i wrong?

[Wahyu]

2mm diameter wire my machine can detected, small lead can detected too, decay at 6us

[mohalothman]

regarding your test, it depends how low you want the delay to be, for under 10us is possible that the wire itself (2mmdiam) can be detectable. 'am i wrong?

2mm diameter wire my machine can detected, small lead can detected too, decay at 6us

guys you'r right, i was experimenting with time sample delay 20us, with shorter delay You have use thinner wire to be undetectable, any way the wire thickness with loop shape has neglected effect in its inductor value the major effect due to the diameter of the loop. so the experiment i did is still valid