XP deus coil modification

[Skippy]

You can't buyit, it's doubtless custom-made for Fisher (like most MD coil cables are). However, you can of course use two seperate cables, (a single-core screened and a two-core screened) or two two-core screened cables. The other possible alternative mentioned on this forum is S-video cable, presumably there's a few 'spare wires' that are unused.

[Henrikras]

Thanks Skippy.. I'll will use the one at the lastest picture, its from and old coil. Earlyer Project I tryed HDMI cable, but I think Microfone cable are better to use, but they are hard to find. I heard that Sommer Cable got the microfone cable we can use, but where to buy 5 or 10 meters, it is a good quenstretion.
Henrik.

[sinclairuser]

for my pi's ive been using guitar cable(audio coax, thick screened) its the best i have found, no silly ohms, capacitance, or inductance readings or changes.
there is a version of this with 2 wires + screen, a stereo version if you will, there is also a 3 wires +screen type, thats used for studio headsets, its the thickness of tv coax but the sheath is soft natural rubber, the wires are 3 multi strand with a copper shield and a mylar wrap, its used for left,right, mike+ and screen.
some of this would do for you, one of the reasons its good for coils, is what you put in one end comes out the same at the other, so at shorter lengths its perfect.
http://professionalaudiocables.co.uk...s/Audio-Cables
have a look, the standards on these cables are european, so find the right one for you and maybe you can find it where you are, if not i can vouch for this supplier and they will sell 3 or 5 meters or whatever you want some suppliers wont.

[golfnut]

If the cable used works, it must be ok.

Did you connect it like this ? What happens to the white wire?




The resistance of the carbon graphite is the lowest Ive seen. 1.5k from side to side is low. That may be one of reasons these are good?

I guess you need to get the sheild resistance down. What was wrong with the performance with Henriks coils?

[Henrikras]

Thanks...
would it not Be this cable link : http://professionalaudiocables.co.uk.../Comus-CAUNC02
0.14 mm wires is Maybee a little thin, but a outer dia 8.5 mm is properly to much. Looks like its a cable which could stand fore a truck rolling over and still work. Good information you gave sinclairuser.

Picture show how the cable was connected... Just like you say Gulfnut, just one change.. The screen/sheild and the White is connected at the plug.
No 1 coil didn't work because of wet grass / chattering. My shielding was to bad.
It could Be because the RX and TX Sheildings was connected in the coil, and not at the PBC or at the Plug.

I have been reading and taking notes of allmust every thread in here, about shielding. Link http://www.findmall.com/read.php?34,1174380
http://www.geotech1.com/forums/showt...heilding-paint
Please correct me If this wrong.
Itsa good idea to get or make the shell grounded (XP and Minelab are using conductive plastic) - Home made version could Be a thin lay of graphite allso outside at the shell. THIS I WOULD MAKE.
You can make the Sheilding in this two version... 1 the shell is like a sheilded case. 2 the two RX and TX coils are sheilded eash. The last one is easyer to work with, because you can use hot glue to fasted and go out to try perfomance before you close it up. The first one is more difficult to test, because the ending lay of graphite isn't possible before it closed. I WILL GO AFTER VERSION 1.
The best perfomance is If you/I can make the shielding lay perfect, to get the same resistance all over...
This could Be done by sand some place and paint some more a other places. THIS IS MY GOAL.
1-2 kilo ohm is sayed many times in the threads and to get that, lower resistance can Be measured at 1 cm. (100-500 ohm)
The connecting wire or wires is done in many ways, but I like how XP had done with a wire from heel to toe.
With graphite powder its possible to make a paint.. (That need some experiments ) I WILL TRY THAT.
Ive ordred this powder.. Link http://cgi.ebay.co.uk/ws/eBayISAPI.d...E:L:OC:GB:3160

All this is in my plans, to make the next coil (no 2 ) perfect.. (If its possible) - BUT ONE THING I DONT KNOW !
How and where do I avoid the loop problem with the Sheilding ??? (Shortblocking)
Is this done by some tape to remove or just by some thin lay so the current drops down ?

Sorry its came long this one.. But I got so many thinks to ask. Thanks for your patience.
Henrik

[golfnut]

OK heres some experiments to try,


with your coil


Wire up as you did, try it and get a benchmark/ reference performance..

then

1) DO not solder the white to anything ( red / black Tx ) (Coax hot and cold/braid Rx ) ( Coil Screen to Rx coax cold/braid)
Any better?


2) As 1 BUT Solder the White to the Rx cold/braid at the box/plug end
Any better?

[golfnut]

It may be your coils are good - and the issue is your screen/ sheild resistance..

What was your rersistance?
what did you use?
what are your construction details?


Im impressed with the xp solution, both the shell and the potting are good low resistance and the drain wire faces the ground rather than being above the coils.



With a metallic shield like aliminium foil - you need a gap so you dont short circuit the mag feild - the coil flux would race around the screen as current.

With a partially conducting screen ( like xp 1.5kohm - side to side) the sheild can be complete annulus, no breaks required - as you dont have a short circuit condition, as ohmic, no large circulationg currents.


Aside from the screening.

Did you manage to find what resonant freq ot the xp Tx and Rx coils?
Did you copy those frquencies in your smaller coil ?

[Skippy]

Quote:"the drain wire faces the ground rather than being above the coils."
Do you think a drain wire above the coil is also a good thing? As the drain wire is undetectable, having more drain wire(s) should be better.
I wonder if XP made a seperate wire connection to the outer shell, or do they rely on the conductive filler etc?

For info, here's an article on surface resistivity:
http://en.wikipedia.org/wiki/Sheet_resistance
Quote:"A very crude two point probe method is to measure resistance with the probes close together and the resistance with the probes far apart. The difference between these two resistances will be the order of magnitude of the sheet resistance."

[Henrikras]

OK heres some experiments to try,


with your coil


Wire up as you did, try it and get a benchmark/ reference performance..

then

1) DO not solder the white to anything ( red / black Tx ) (Coax hot and cold/braid Rx ) ( Coil Screen to Rx coax cold/braid)
Any better?


2) As 1 BUT Solder the White to the Rx cold/braid at the box/plug end
Any better?

Dear Gulfnut ... The coil is thown away. New project is started.

[Henrikras]

It may be your coils are good - and the issue is your screen/ sheild resistance..

What was your rersistance?
what did you use?
what are your construction details?


Im impressed with the xp solution, both the shell and the potting are good low resistance and the drain wire faces the ground rather than being above the coils.



With a metallic shield like aliminium foil - you need a gap so you dont short circuit the mag feild - the coil flux would race around the screen as current.

With a partially conducting screen ( like xp 1.5kohm - side to side) the sheild can be complete annulus, no breaks required - as you dont have a short circuit condition, as ohmic, no large circulationg currents.

Aside from the screening.

Did you manage to find what resonant freq ot the xp Tx and Rx coils? YES this was easy. I found out that the XP Stock coil with 15.9 and 10.4 mH was a little to low at my own coil to get same resonans, Thats why I added some turns. Something like 15.95 and 10.45
was spot on and the coil did work perfect in lab.
Did you copy those frquencies in your smaller coil ?

YES.

[Henrikras]

Thanks - try to understand everything you say, but ist a little hard.
Its allso to difficult to explain what I'm going to do, so I go after some fotos.. And a hand drawn drawing.
With these I will try to show you my plans...and at the same time, tell you "did I understand what you said" so you can stop me, before its to late.
I should had been more in English lessons at school.. Got 100-200 words to work with, so its Very difficult to tell every correct.
Henrik.

[Henrikras]

Okay this should show step 1-2-3...

[Skippy]

I'm not sure how essential it is to have graphite on the outside of the coil case. After all, many commercial coils do not have conductive plastic - any white plastic case will definitely not be conductive, because black carbon dust is added to make the plastic conductive. Plus, the graphite will wear off easily with use.

However....If you want to try it, I suggest using more connections between the outside and inside, maybe add two near the centre of the coil case?

Making a good electrical connection between graphite and bare wire is not easy, and so the more contact points the better. I think using multi-stranded wire may be worth considering, such as 10 /0.1mm ( 10 strands of 0.1mm diameter). Inside the control box of my F75, there is a painted graphite shield on the case. A 10 /0.1mm PVC insulated wire has 20mm insulation removed, the wires are spread out in a ' Chinese fan', and the end 5mm of the wire is taped down. The paint is then applied over the case and the bare section of the wire.
I will attach a drawing with some suggestions on how to fit these in/out wires, later. [done]

I think your attempt to even out the surface resistance measurement is too ambitious, and probably will make no difference. Only do it if you think you have a particular 'bad' area, where you perhaps had difficulty applying the paint.

[Henrikras]

I understand Skippy..
The two first wires 0.10 is now at place. I will try to measure a little, it will give some ideas where I am.
then I can add some more wires and take it from there.
pictures showing before and after first paint. (Only two wires front and back 0.10 mm)

[golfnut]

nice shells from don there.

I guess the side to side resistance of the xp shell is good also due to the cross web supports that go from centre inner to outer so you get additional low R path.


On the drain wire, I normally fit to the shell, then coils, then pot.

The e field charge will exist and vary between the coil and the ground. To me it makes good engineering sense to have your drain in there between the ground and the coils, rather than above the coil ( where I normally put the drain ).


Henrik what is the resistance of your shell - side to side ? Is it even dry yet! The R goes lower as it dries.

For info, i normally do drain like this. I use the thin wire from a small multistrand wire