New spin on a old friend. 3Dss holllow core wind.

[baum7154]

Hello all,

Long time since I have been in forum.

I would not recommend immersing the coil in anything as air is the best (short of a vacuum) at keeping capacitance low.

Looking at the photos in the first post there is a lot of parallelism between the inner wires although they are separated from each other. The 3DSS pattern is designed to have the wires cross each other at about 90 degree angles with lots of air in the construction to keep capacitance low and coil speed up.

The 3DSS photo of the overwrap of the last few windings is beautiful and demonstrates that lack of parallelism.

Best regards and happy building,

Dan

[godigit1]

If you are going to try again, perhaps you can immerse the whole thing in white glue for few minutes, allowing good penetration. Then remove and allow to dry, remove pins and give another good white glue bath.
Or maybe better to use sanding sealer, same immersion process, then allow to dry. it should be rigid enough to remove the pins.
you are certainly a man blessed with massive powers of concentration and patience. I would've headed for the closest watering hole after such a debacle .

Yes Fortunatly the watering hole is well stocked.
I think i may try this agian but im not sure about the litz at the moment so far ive not been that impressed and weve gone a few rounds now just on my first coil.
I dont like the way it doesnt holds form, the inner wires can be misalligned from handeling as you wind the next layer. Seems it makes for sloppy inner wraps.
I realligned some of mine with a tooth pick when i finished the coil.
I do seem to be a gluttin for punishment though as ive been considering my next exercises in tedium.

Not to sure about the figure eight, still debating that one.
Hard to build the circuits I want to right now since Im on the road so coil time it is.

[godigit1]

Hello all,

Long time since I have been in forum.

I would not recommend immersing the coil in anything as air is the best (short of a vacuum) at keeping capacitance low.

Looking at the photos in the first post there is a lot of parallelism between the inner wires although they are separated from each other. The 3DSS pattern is designed to have the wires cross each other at about 90 degree angles with lots of air in the construction to keep capacitance low and coil speed up.

The 3DSS photo of the overwrap of the last few windings is beautiful and demonstrates that lack of parallelism.

Best regards and happy building,

Dan

Hi Dan ,
Good to see you here again.
I want to first say thank you it was your race track coil that has been a inspiration me to experiment with these coils.
Ater biulding this one
Some of the problems you faced such as a tight inner radius at the corner became aparrent. Thats when I started thinking of a round form.
The way the wires bunched to the inside of the corner and the pionts grew on the outer edge looses form.

I dont know if it will really be any better than the traditional wind but one place I do think it is improved form the traditional form is at the slots themselfs.
The wires pinch together there and stack tightly I think I have eliminated that. Once angain any rael benefit is still to be seen.


On the second photo in the first post where the wires are parallel, that was a test wrap to see what it would look like if I did not skip a slot on the wind.

Is this the parallelism you are refering to Or the inner winds of the finished coil?

It took ten wraps before transition that way. So The last photo is the traditional 3dss wind but I skip back to another hole form like having all the slots on the traditional form and using them. this also gives two wire gaps between the layers as you transition sides.

Do you think any of these changes are beneficial enough for me to continue in this direction?
Best reagards,

[baum7154]

Yes the parallelism I referred to is in the first photo. Is the pattern in the third photo showing all of the windings in the coil? In other words the parallelism noted in photo 2 is not underlying the cross hatch 3DSS visible outer windings? If so, I’d continue with your testing.

By the way, the 3DSS RACE TRACK coil I posted some years ago was used yesterday to quickly find a piece of jewelry I made for my grand daughter in 6” tall grass in the back yard. It allowed rapid search of a wide area using my CHANCE PI DETECTOR. The race track coil used is actually faster than my 8” round coil of original design. The bunching in the corners of the racetrack coil was solved with slightly deeper slots and tying in the windings with floss.

Dan

[godigit1]

Hi Dan.
Thank You,
Yes the black and green wires were removed they were just experimental . it was still the 3dss pattern wrap but without skipping a slot.
Its good to hear the race track coil is working good and your putting it to task. Why do you think it ended up faster than a traditional 3dss round?

Before I destroyed this coil I only got the chance to test it at 450us. I was able to sample down to 8 us at 5 us it got a bit chatty Mostly due to the long lead wires not being shielded I think.
Im debating weather to use more of the litz I used before or make my own wire as in The crazy litz thread . except not to that degree.
No litz is designed speciffically for metal detecting, were left trying to find a good match that will work.
Looking at the frequency charts for below 10khz less strands are needed and skin effect is almost nill so that really shouldnt be a concearn. The only benefit to litz i can really see is a reduction is resistance so smaller strands can be used.
This reduction comes form the wires being insulated from each other allowing them to act as parallel resistors.

My bid for a custom made litz is going to be 4 strands 30 guage= two strands twisted left, two strands twisted right then those twisted together left handed and finally wind the coil right handed. Also I can use wire that has a thicker coating than enamel for less capacitance. Im still debating Kynar or pvc for the insulation.
Thought about teflon but im reading all teflon wire either has to be plated with silver or nickle.
I didnt really want to elicit a friend into my madness to help with the wire so I started a twisting machine, it will also wind flat coils when I am done DD flats is next on the experiment list.
Here are the gears for the forward and reverse gear box. .

Thanks again.
.

[baum7154]

Hi Godigit,

Regarding the speed difference between the round VS the RaceTrack coil I don't have a real explanation other than the Racetrack is 7uh less inductance than the round one. Perhaps re-running the round coil damping may help. As you describe, sampling below 7us tends to get chatty...unavoidable I think.

Getting rid of the skipped slot or pin in winding the 3DSS deletes the perpendicular crossing between layers and raises paralellism/capacitance.

I think the PVC insulated wire has similar dielectric performance to Teflon but it does suffer from temperature degradation when warm.

Teflon wire is generally silver plated in one of three thicknesses. I remember detailing this years ago in this forum according to the mil spec numbers. I believe it comes 'Flashed or Washed' , 'Plated', & 'Clad' in increasing thickness. You want the thinnest one which is the 'Flashed or Washed'.

Dan

[baum7154]

BY the way I have not seen tin plated copper with Teflon insulation. I believe it is mainly produced in silver because the heat required for Teflon jacket extrusion is best protected against oxidation/corrosion with silver coating.

[godigit1]

Wow Say that again. Thats just out of line. Looked up some tefon wire and to build what I want would be almost $200 for 200 feet whch is what I need to make one 50 ft 4 wire custom wire.

I guess its beacuse the tsunami in Japan took out one of the main makers of Ptfe itself. So there has been a worldwide shortage is what im reading.
If I had the perfect coil allready designed it might be worth it but I would really still debate it. What does a coil need to withstand so much heat.
Yes it has a better dialectric constant.
But with that comes a thinner coating to get the same 600v rating so it seems there is really alot of give and take.

My question as far as capacitance goes is do we benefit by the slightly better dialectric value with less thicknees more?
Or is the extra spacing with the same 600v rating going to provide a lower capacitance even though the Dialectric values are slightly less.

One other thing to consider is I think is whats called leakage at higher frequencies which Pvc does well at, at least better than Kynar.
Im going to design my own wire ( aaaaaaaaaataboy ) I give myself a snow badge. LOL
Any way Looks like 4 starnd 30 awg is equivelant to 24 guage I was shooting for 26 so I may have to get 32 guage for 4 strands to work.

I need allot of wire and on ebay I can get a 1000 foot of pvc wire for under 20 bucks but i have to wonder about the quality at that price. At least could experiment with a few twists.

[godigit1]

BY the way I have not seen tin plated copper with Teflon insulation. I believe it is mainly produced in silver because the heat required for Teflon jacket extrusion is best protected against oxidation/corrosion with silver coating.

Ive found nickel mentioned as the under plating curious how that would be since it is a lower conductor.

[baum7154]

Regarding Nickel plated wire, nickel itself is about 4 times more resistive than silver and tin is about 6 times more. That resistance helps to subdue eddy currents. I think the Teflon insul nickel plated wire is worth a try for a faster coil perhaps in the 4-5 us range.

Regarding the 26awg wire vs 24awg the resistance difference my coils is about 2 ohms for #24 and about 3 ohms for #26 of same construction.

Dan

[godigit1]

Hi Dan,
Are both these coils single strand coils?
Ive been thinking and trying to understand the dynamics of a coil. Please correct on any of this if im off base.
To get to sub 8 us and be able to hear the targets we want (micro jewelry , nuggets)we need a fast coil with low noise and great sensativity.
Quite the balancing act.
So addressing the issues. issue 1
Inner wire capacitance.
My thinking on this is custom wire should be made for this and purposes of Emi cancelation.
How ?
use a twisted pair to construct a coil wire. but thats litz we allready have . Yet the litz is not custom designed to our purposes.
How can I take this to the next stage?. Design and twist my own wire.
Heres where it gets tricky. How many strands? what twist per inch ? Forward or reverse twists , combinations of both, Strand size coil configuration?
the list goes on.
So why not throw all the tricks we have up our sleve at each issue.
My bid for a first spin.

Wire. 4 strands is enough i think two twisted counter clockwise two clockwise. The wire should have a coating thicker than enamel.
Im going to try Pvc at first for experimenting beacuse of cost.
Im still looking at twists per inch for proper frequency for our use.
Then we have to have a balanced coil. So DD made from this wire. And Im thinking a flat spiral DD variation. TX Wire stack would be verticle five rows high and progress 5 rows wide for a Square bundle. Rx Experiment but maybe two high ten wide.
Thats where Im kinda at.
https://www.v-cap.com/awg-calculator.php
Here is a wire bundle to guage calculator that gives you resistance as well.
Looking at 4 wires.
30 awg would be 24 awg with a resistance or 1.4 ohm per fifty feet
32 awg is 26 awg at 2.24 per 50ft.
I still have allot of choices to make so any input would be helpeful. Im trying to put all these ideas together form around the forum and what my understandings are of allot of different threads so please let me know if im left field
Thanks

[baum7154]

After building many types of coils I only build 3DSS MONO COILS because any of the others require an additional shield and that shield adds capacitance. When you are seeking small gold/jewelry it is great if you can operate with 5 us sample delays or even less. A flat spiral coil while quite fast when unshielded gets slowed down when the required shield is applied and I doubt a graphite shielded 300uh flat coil will operate at 5us sample delay.

The wire I use is #24awg 600 Volt 19 strand Teflon insulated. The 19 strand has great flexibility when twisted as a continuation of the coil wire and used as a feedline. I recommend using even higher voltage insulation to get greater inter-wire spacing to effectively lower capacitance. It would be interesting to have the same wire with nickel or tin plating.

Dan

[godigit1]

Im am thinking that with a opposing twisted wire configuration I can gain the same benefit as a 3dss type coil or figure eight type. This eliminating the need for a schield.
Emi and EFI should cancel equally in the opposed twisted pair. The whole coil would be would as a special twisted set of pairs as Similar to Sean Goddards Mad litz thread.
Is this possible do you think?

I still intend to try this type of wire in the 3dss from as well.
One thing Im concearned about is if a twisted pair cancels out Small magnetic signal interfearance is this going to work with EFE and will it degrade Low tc signals.

The supelness of litz and the 19 strand is both a benefit and a curse as far as Im concearned. Beacuse it is hard to lock into form and disturbes layout as you wrap succesive layers.
The types of forms Ive been trying require me to lock in the wires so I can remove the form partially of completly as in my Older formless coils I was trying to make. They performed well but if you remember they were considered not fully self schielding.
Im looking at making better solvent resistant litz and or find very thin encapsulants to lock things in at every 5 layers.
Picture something like hair spray but slovent free and non conductive at higher voltages.

[Cazavor]

Your coil in the first post looked very nice and inspired me to have a go at it.

While making this I learned a lesson of my own - don't trust cable rolls to be one continuous piece. The 100 m 0.141 mm2 PVC roll I bought was in fact made of multiple segments like 30 m. Luckily that was just barely enough for my coil.

Anyways I filled a 16 mm plastic electrical conduit with sand, taped off the ends with aluminium tape, heated it to 85 C with a heat gun and bent it into a round shape around 8-9" in diameter. Then drilled 74 holes through the form, put a toothpick through each and started wrapping the wire similarly to the original post (I believe).

Here's the coil with 15 turns wrapped:


And with all 35 turns:


After wrapping with tape and cutting the sticks:


Now for the results, not as great as I expected really. Mega328 component tester measures inductance at 360 uH. Multimeter gives resistance 3.6 ohms. With my analog scope and x10 probe I measure SRF to be around 820 kHz without coax, which indicates a capacitance about 105 pF. The self-shielding properties of this design are evident though - on 10 mV / div the noise difference is noticeable on the scope when switching the leads. I have yet to finish the mechanical construction of a detector to test this coil in action. And the construction of the coil too of course - especially the mounting and a protective layer.

[MartyJ1963]

Won't the Aluminium tape that you taped the pipe ends with act as a target? Regards, Marty