spiral pi coil

[godigit1]

For what its worth my professional made small gold detecting coils that detect .06 and .1 gram nuggets are very low resistance .6-.7 -.8 ohm,
that would help to discharge the coil quickly.

Hi 6666,
I was wondering what type of coil this is and wire type is used in the construction if I could ask?
Shielded?
Thanks

[green]

Hi godigit, interested in what you learn with your experiments. Other than speed(SRF) I don't see much difference if inductance, size and Tx profile are the same with the things I've tried. Haven't tried a 3DSS. Been using figure8 Rx with a Tx surrounding Rx. Less noise and reduces ground signal are the main reasons.

[6666]

Hi 6666,
I was wondering what type of coil this is and wire type is used in the construction if I could ask?
Shielded?
Thanks

Hi clogged up with a cold will try and reply when my head stops spinning

[sinclairuser]

latest experimental coil, made from .5 mm plastic shielded nickle plated wire, the wire is 5 .1mm strands twisted together.

please ignore the pic below i removed a jpg from the line above as it was too blurred, but when i posted it appeared at the bottom.

[kt315]

potato camera. no light.
read here https://www.geotech1.com/forums/show...here-share-out

[godigit1]

Hi godigit, interested in what you learn with your experiments. Other than speed(SRF) I don't see much difference if inductance, size and Tx profile are the same with the things I've tried. Haven't tried a 3DSS. Been using figure8 Rx with a Tx surrounding Rx. Less noise and reduces ground signal are the main reasons.

Hi Green,
Sorry for the lag on response,
Im sure your right im not going to find some silver bullet. I think any real benefit is going to come in a new type of design.
I keep trying to design variations of coils with possible improvements but I need to structure my testing properly.

On your Figure eight coil what are the tx And Rx values?
I recently wraped a figure eight spiral coil but missed the Mark as far as inductance by a 100uh.
The coil calculator said I should have had around 360uh.
This is a case I think or example of your statement that spiral coils seem to work better if wraped with no spacing.
On this coil there is allot of spacing I think too much so its not getting full inductance.
It only came out to 200uh.
Thinking of trying it in a configuration like you are using DD style or adding another coil make it two field.
I living in a house Im remodeling so testing anything is difficult but I just got a room finished and setting up a small station to work.

This is the coil design at the moment.
It should be low capacitance as everything is spaced and any wire crossings are at 90 degree angles the layers in the 8 crossover have silicon flex tape between them its suposed to have a 8000 volt rating. all other wires are coated with super corona dope with a 4100 volt rating. Allot of work to find out my spacing is too much I think.

[godigit1]

Hi clogged up with a cold will try and reply when my head stops spinning

Hi 6666,
Hope you are feeling better. I was just curious what type of coil it was.
No Hurries no worries.
Be Well

[godigit1]

[ATTACH]46987[/ATTACH][ATTACH]46988[/ATTACH][ATTACH]46990[/ATTACH]

latest experimental coil, made from .5 mm plastic shielded nickle plated wire, the wire is 5 .1mm strands twisted together.

please ignore the pic below i removed a jpg from the line above as it was too blurred, but when i posted it appeared at the bottom.

Hi Sinclairuser.
Is that wire multi color wraped or have you joined multiple peices together?
The .1 mm strands are around 38 awg equivelent.
Do you have supplier info on this wire?
What is your inductance and resistance on this coil?
Thanks

[green]

Hi Green,
Sorry for the lag on response,
Im sure your right im not going to find some silver bullet. I think any real benefit is going to come in a new type of design.
I keep trying to design variations of coils with possible improvements but I need to structure my testing properly.

On your Figure eight coil what are the tx And Rx values?
I recently wraped a figure eight spiral coil but missed the Mark as far as inductance by a 100uh.
The coil calculator said I should have had around 360uh.
This is a case I think or example of your statement that spiral coils seem to work better if wraped with no spacing.
On this coil there is allot of spacing I think too much so its not getting full inductance.
It only came out to 200uh.
Thinking of trying it in a configuration like you are using DD style or adding another coil make it two field.
I living in a house Im remodeling so testing anything is difficult but I just got a room finished and setting up a small station to work.
[ATTACH]46999[/ATTACH]
This is the coil design at the moment.
It should be low capacitance as everything is spaced and any wire crossings are at 90 degree angles the layers in the 8 crossover have silicon flex tape between them its suposed to have a 8000 volt rating. all other wires are coated with super corona dope with a 4100 volt rating. Allot of work to find out my spacing is too much I think.

Reason I think zero spacing is best for spiral coil(flat spiral.jpg)capacitance is less than 10pf. My first attempt at a spiral coil wasn't good so tried a flat basket which worked. Tried a flat spiral again awhile back, success this time. Not sure which is better.

Picture of the 8inch figure eight coil I'm using, COIL Tx(oval) Rx 2(8inrd).jpg. Both Rx coils are wound the same way, put next to each other(one not inverted), outer wires connected. Inner coil wires used for Rx coil.

Not saying it's best way or even a good way to make a coil. Seems to give best detection distance of the things I've tried. Interested in what others are trying to see if there is a better way.

Figure8 Rx probably needs absolute valve circuit since each Rx coil gives opposite polarity signal?

[sinclairuser]

Hi Sinclairuser.
Is that wire multi color wraped or have you joined multiple peices together?
The .1 mm strands are around 38 awg equivelent.
Do you have supplier info on this wire?
What is your inductance and resistance on this coil?
Thanks

hi godigit1, the wire is quality 6 core alarm wire, i only had a 10m length at hand so joined it together the joints are as small as possible with heat shrink on, as this was a basic test just to try this coil i didn't think the joins would matter, i have made coils before using this way of joining wire and as long as the solder joints are tiny with minimal LEAD solder they dont seem to matter.
i scrounged this wire from a mate but if this coil works i intend to make an other one using a single unjoined strand since he says i can have the roll.
i will post the specs later on as i'm returning home today.
thanks,
aly.

[sinclairuser]

hi all, the specs of this coil are 30 turns, 370uh and 21ohms!!!!!.
so i guess this is useless too.

[green]

hi all, the specs of this coil are 30 turns, 370uh and 21ohms!!!!!.
so i guess this is useless too.

Wondering what the SRF of your coil is. If you have a scope connect the scope probe to the ground lead making a loop. Place the loop on the test coil, place the test coil near a operating PI coil to excite resonance in the test coil. Read the decay frequency off the scope. Wondering if spacing gives lower capacitance than no spacing. Have you connected the test coil to a PI and compared detection distance with another coil?

[sinclairuser]

hi green, i was reluctant to use this coil 21 ohms is the highest iv'e built(pi), the frequency comes out at 961.841hz.
trying the coil on a barracuda it is about 1-2 inches less than its 8" bundle wound .5mm magnet wire coil, however the mono loop i made for the barra is bang on spec in fact when i made it i left the 330ohm resistor as it wasn't ringing enough to mess about with it.
so tuning the damping resistor on the barra for this flat basket spiral may bring the distance up, but the barracuda is not the detector i want to run this coil on.

[green]

hi green, i was reluctant to use this coil 21 ohms is the highest iv'e built(pi), the frequency comes out at 961.841hz.
trying the coil on a barracuda it is about 1-2 inches less than its 8" bundle wound .5mm magnet wire coil, however the mono loop i made for the barra is bang on spec in fact when i made it i left the 330ohm resistor as it wasn't ringing enough to mess about with it.
so tuning the damping resistor on the barra for this flat basket spiral may bring the distance up, but the barracuda is not the detector i want to run this coil on.

Thanks for the SRF. Calculates 74pf with 370uH. Lot more than 10pf I get with zero spacing. Have seen spacing suggested for a spiral coil in quite a few threads. Haven't seen an example where spacing caused a lower SRF(less capacitance). Maybe another reason why spacing would make a better spiral coil?

[godigit1]

hi all, the specs of this coil are 30 turns, 370uh and 21ohms!!!!!.
so i guess this is useless too.

21ohms does seem high.
If I got the individual strand size correct .1mm is equivalent to 38 awg.
5 strands is equal to 31 awg finished wire size.
If I calculate for a 8 inch coil 60 feet of line 18.28 meters.
the resistance is .432794ohm/m for 5 strands 38 awg.
So Im getting 7.91 ohms or there about. you have three times what I calculate I must be way off on the wire specs or something.
Is this wire individually insulated like litz? maybe some strands did not solder well.