spiral pi coil

[sinclairuser]

hi all i have tried to make a flat spiral coil, it is outer dia 14cm, inner dia 1cm, 35 turns.
it reads 0.04 mh and 0.9ohms, its wound out of .6mm bell wire but reads 0 cap.
so i'm not convinced its right, does anyone have a good spiral coil calculator, the ones ive found seem to be useless, or want to install stuff on my computer.
thanks,
aly.

[6666]

Any chance you could show a picture of your coil so we know what we are dealing with ? those figures dont sound right

[dbanner]

N represents the number of turns off wire
At the bottom of the page there is a flat spiral formula with diagram
This formula good for the ballpark, close to your target inductance. Good enough for rough calculations that will give reasonable results. The gauge of wire 0.4 to 0.6mm not so critical to the outcome, very small difference it makes.
Microhenries for L but inches for other parameters, not that metric system rubbish
The table on the left is used to find no of turns per inch for any gauge of wire, good to know for arriving at value of b in formula. Should be able to transpose formula for solving number of turns required given other parameters. Old school, yes.

[sinclairuser]

Any chance you could show a picture of your coil so we know what we are dealing with ? those figures dont sound right

yes bruce i will stick a photo up.

[sinclairuser]

N represents the number of turns off wire
At the bottom of the page there is a flat spiral formula with diagram
This formula good for the ballpark, close to your target inductance. Good enough for rough calculations that will give reasonable results. The gauge of wire 0.4 to 0.6mm not so critical to the outcome, very small difference it makes.
Microhenries for L but inches for other parameters, not that metric system rubbish
The table on the left is used to find no of turns per inch for any gauge of wire, good to know for arriving at value of b in formula. Should be able to transpose formula for solving number of turns required given other parameters. Old school, yes.

thanks dbanner.


for some reason it chopped of the ends, but i have tested it as a single wire, and twisting them together(doubled up) doesn't make much difference.

[dbanner]

COIL32, it's free and has good spiral coil calculator.
It is small program, easy to install .exe file.
Check out this guy winding a flat spiral for the surf pi.
https://m.youtube.com/watch?v=LFZpy4sdZuk

[6666]

thanks dbanner.

[ATTACH]46775[/ATTACH] [ATTACH]46776[/ATTACH]
for some reason it chopped of the ends, but i have tested it as a single wire, and twisting them together(doubled up) doesn't make much difference.

Thanks photo, the geometry of your coil is giving low inductance, the small circles in the middle create little flux

have a look at geometry of this design, https://www.youtube.com/watch?v=_HS7-Y7P0hI

[6666]

COIL32, it's free and has good spiral coil calculator.
It is small program, easy to install .exe file.
Check out this guy winding a flat spiral for the surf pi.
https://m.youtube.com/watch?v=LFZpy4sdZuk

Thats an unusual way to lay the wire down, but what ever works , must be very sticky tape.

[green]

thanks dbanner.

[ATTACH]46775[/ATTACH] [ATTACH]46776[/ATTACH]
for some reason it chopped of the ends, but i have tested it as a single wire, and twisting them together(doubled up) doesn't make much difference.

Wondering what the SRF of your coil is. Thinking SRF of finished coil, shielded or not shielded with lead(coax or twisted pair) is important reading. https://www.geotech1.com/forums/show...552#post258552 is the way I do it.

Looking at my measurements I see I didn't make the SRF measurement with the finished coil. Probably a little higher than the circuit resonance measurement.

[godigit1]

COIL32, it's free and has good spiral coil calculator.
It is small program, easy to install .exe file.
Check out this guy winding a flat spiral for the surf pi.
https://m.youtube.com/watch?v=LFZpy4sdZuk

You dont even need a form to make a coil this way just print the shape and wrap to it..
These are dirty they have been lying around for the last six years.

[Carl-NC]

The inner windings cancel the flux from the outer windings. You need a much larger hole in the middle.

[sinclairuser]

thanks everyone, i will keep messing and when i have figured it out i will report back.

[green]

You dont even need a form to make a coil this way just print the shape and wrap to it..
These are dirty they have been lying around for the last six years.
[ATTACH]46781[/ATTACH]

Do you use spiral wrap coils on your detector or have you found a way to make a better coil?

[godigit1]

Do you use spiral wrap coils on your detector or have you found a way to make a better coil?

These two coils were my first attempts at spiral coils. I intend to experiment with several veriations. I believe Ive come up with a unique figure eight spiral design.
Its still just on paper and im trying to work out the form.
Ive been at a standstill due to work and research lately.

[godigit1]

P.s
To actually answer your question. I use all profesional coils on my detectors.
Ive been able to make nothing that will beat them yet. Ive had some pretty good ones but no winners. On my kt315 1st edition baracuda the yellow coil you tested was very good.
I now think that it was a accidental match to that detector ,got something right.
Also this is off topic a bit but that baracuda is really partial to the type of diode used.
That coil with a high intensity green led performed right up there depth wise with my MPP and a 12 inch dual field. Ive yet to remake it but have been saving that spool of wire.