Chance PI coil...

[eclipse]

The shielding doesn't have to do anything with the iron in the ground. You are shielding the coil against the earth field and that is if your detector has primary sampling delay of 10us or less. If you sample at 15-20us earth field effect is relatively low thus doesn't effect the performance of the device. To get good performance on small items such as coins you need delay 10-20 us at most.

[Matt_Rowe]

I was thinking on building one of these coils, but i still dont quite understand the winding procedure, do i pick any hole to start, preferably by the exit on coil shell, and then how many spaces in between top and bottom or inside row,so lets say, start on inside,then go 3 spaces to outside,then 3 to inside, ect, or alternate to get a good even pattern.

[MartyJ1963]

Hiya Matt. I hope this little 3DSS Tutorial I've done is of use to you and hope you can follow it easily enough. I'll make a short video how to wind one when I can find some time away from the many chores I have at the moment. Good luck building! Let me know how you go. Regards, Marty.

[Matt_Rowe]

Thank you ,marty, thats perfect,cheers for the holidays and new year.

[SkyeHi]

MartyJ1963
Thanks from me also. I have a Clone kit just finished, thought I would try a 3dss coil out on it and one for the Baracuda that I have just started. These first two coils will be round with different radius and will compare them to a 3dss elliptical of similar surface area.
I was impressed by the attention to detail and testing results done by baum7154 on this coil/Chance project.

[MartyJ1963]

You're very welcome. I haven't got around to making that video yet as I've had tons of chores to finish on the house first,,but I will definitely get around to doing it as soon as I can. Regards, Marty.

[Coolmakina]

Hi
what if we made a 5 turn on a small coil, overlaped a 2nd (bigger) and another 5 turns, overlaped 3rd (bigger) and 5 turns, overlaped a 4th and another turns....
something like this...

[Coolmakina]

draw

draw

[SkyeHi]

MartyJ1963
[added] There is a question at the end of this
I have wound several of what Baum called 3DSS coils, none have come out with the inductance looked for [300uH +]. I have been getting 190 to, my best so far, 240uH, this for 210 to 225mm mid point dia coils. At first I thought it might be the gap between the apex of the slots in the outer and inner dia being too distant, affecting flux ddensity, or something. The differing circumference does cause a thinning of the wind on the outer compared to the more bunched windings on the inner. I made a couple more formers in 2mm acrylic [a nightmare to machine, superglue is handy] but still only reached 240uH for 5 and a half layers [ran out of wire].

For ref.
210mm coil wound 3DSS style with 0.5mm [24swg] solid enamelled gave 190uH. Same former wound with 24swg stranded teflon gave 200uH with 5 layers wound on.
Sorry Marty for my lack of brevity but here comes the question;
I counted the strands on the wire I was using, 6 strands. On your helpful diagram above yours was 16 strands.
Could this be the solution to achieving a good inductance value, my lousy 6 strands needs to be 16? Is my teflon stranded little better than solid wire?
If you reached this far Marty, well done and thanks.
Fine regards,

[MartyJ1963]

Hiya SkyeHi. When I first started out making 3DSS Coils I tried different wires from 7 stranded down to single strand ordinary copper enamelled wire. I always achieved 300uh or slightly higher:- if the inductance was lower or higher I would either remove some wraps or add some. One hing I think I've noticed is the 3DSS Tutorial I uploaded. I just quickly looked at it again and there's a slight mistake I've made in writing it. I meant to write that each layer consists of 5 revolutions of wrapping to complete one layer and there should be 6 layers in total to achieve 300uh or very near. Sorry about that! If your slightly under 300uh, and 300uh is what you want, then add a little more wire. By the time you've wrapped 2 layers of medical tape it should be around 300uh. Hope this helps. 6-7starnd wire will work ok but 600v 16 strand will ive a lot better results,,,,or even 400v wire. Regards, Marty.

[SkyeHi]

Thanks Marty, and I never noticed the error. I was working on the need for 30/32 windings anyway, 6x5.
It was the similarity of inductance value from solid to my stranded that made me question, "Could 16 strands make that much difference."
Have put the heater on in my shed come workshop I thought I would check the SRF before I unwind the 240uH coil. Need the heater on, it is baltic here 2 degrees and a gale of wind trying to remove skin with little prills of snow.
Fine regards Marty,
Alan

[MartyJ1963]

Hi Alan, I know how you feel about the weather! I do a lot of my work outside. I've been building a new bench Grinder for the past 2 weeks (2 x 72) and today must have been the coldest so far. There's no catch or lock on the inside of the shed door (yet) so the wind's been howling through and the snow we had today was gathering in the shed door way! Lol. I could only manage about 2 hours on it cos' I couldn't feel my feet or fingers. Glad I do my soldering indoors! Lol. Let us know how your coil progresses. Regards, Marty.

[SkyeHi]

The coil seemed to resonate at about 1.16mHz.
"seem" and "about" because the wee Chinese signal generator is a bit unstable and it's max out is around 1.15mHz. Was after one on ebay, a Farnell but just missed out. Will have to have another look or see if there is a decent kit to build.
I have more wire coming and by the time it has arrived I should have a couple more formers ready for winding.
I have a couple of diesel heaters to check over, I'm going to put one in my wee work shed. On a low setting they burn about 0.1ltr per hour. I'll put it on a timer and drawing the air from outside it'll help keep things dry.
I'll let you know how I get on with the coil building.
Fine regards, Alan

[dbanner]

The coil seemed to resonate at about 1.16mHz.
"seem" and "about" because the wee Chinese signal generator is a bit unstable and it's max out is around 1.15mHz. Was after one on ebay, a Farnell but just missed out. Will have to have another look or see if there is a decent kit to build.
I have more wire coming and by the time it has arrived I should have a couple more formers ready for winding.
I have a couple of diesel heaters to check over, I'm going to put one in my wee work shed. On a low setting they burn about 0.1ltr per hour. I'll put it on a timer and drawing the air from outside it'll help keep things dry.
I'll let you know how I get on with the coil building.
Fine regards, Alan

An alternative way to measure coil self resonance (srf) is to use a 74AC14 chip to generate a square wave oscillator. (Simple circuit)
Then drive the coil with square wave and measure the ring down on oscilloscope. Very easy.
See W2aew video #87 and #90 on YouTube.

[SkyeHi]

dbanner, thanks. I'll go have a look at using a 74AC14 chip.
Had another attempt winding a 3DSS coil this afternoon, 420uH and 2.3ohms on a 270mm coil. A bit bigger than I was wanting, was making best use of the acrylic offcut I had, the smaller dia came out of the centre. Some eedjit cut adequate depth slots in the large dia and insufficient depth in the former that was likely to need more windings. I'm pleased, it looks good and has adequate L to reduce the winding, will try it out on the Clone MD.