PCB mono coil

[Altra]

Hi Tec,
You are right. I was using 1oz copper for my pcb, so the higher resistance. Pancake or spiral wound coils are the least efficient. Better to have square or round profile , so that all the inductors can interact.

If I were spending the money. I would do a 4 layer with 6 or 7 turns per layer. Don't worry to much about the resistance, some of Eric Fosters best beach detectors had series resistance of 3 ohms plus he would add a 27 to 39 ohm fixed resistor between the mosfet and coil. This acted as a current limit and also sped up the recovery for early sampling.

What did that proto coil cost, if you don't mind saying?

[WM6]

Nice CNC router Altra, and milling work!

Only as interesting info: coil proposed in this topic here was invented more than 40 years ago:

[Altra]

WM6,

Thats interesting, I could not enlarge the image? Maybe upload again? Tesla was using spiral coils a 100 years ago.

Thanks for the comments.

[WM6]

WM6,

Thats interesting, I could not enlarge the image? Maybe upload again? Tesla was using spiral coils a 100 years ago.

Thanks for the comments.

Sorry for bad resolution. This was due to JPEG format - need to be renamed in JPG.

This was PCB spiral and PCB shielding.

[Altra]

Thanks

[Tec]

PCB cost

The pcb cost 80 tooling, 29 dollars each.
ourpcb.com


That patent is awesome I think the inventor knew his stuff.
He has the spirals becoming more dense towards the outer edge, interesting.

[WM6]

He has the spirals becoming more dense towards the outer edge, interesting.

Good noticed.

[Aziz]

Hi guys,

the PCB coils aren't the money worth. Really, too much expensive and have less benefits.
(Yup, I have made some PCB coils, even some very complex induction balanced coils too.)

He has the spirals becoming more dense towards the outer edge, interesting.

BTW, this is to keep the shielding to coil capacitance density constant. No rocket science.

Cheers,
Aziz

[bernte_one]

high resistance

hello

i follow this thread and seems that i have to repeat it.
an easy solution to decrease the resistance is to increase the diameter of the copper tracks
i can recommend rosol 3 its a paste of solder fluid with tin

and coil shield can be done by a mixture of fine graphite powder and clear laquer

hope this works good for all

regards

[F117]

I had 4 of these PCB coils on the shelf for a couple of years now.
Finally had some time during the holidays to turn them into a search coil prototype.
The layout was published here by George : http://www.geotech1.com/forums/attac...5&d=1337436177




A single PCB coil measured 191 microHenry





2 of these in series and stacked on top of each other measured 568 microHenry = 3 times the single inductance due to mutual inductance.







To turn this into a practical search coil, I turned both PCBs facing each other - with the traces at the inside and the epoxy PCB bottom at the outside, with a piece of plexi glass in between as separator/insulator.




I cut some holes in the plexi plate for the inter PCB connection - at the outer side of the coil - and the cable connections = the 2 inner connection points of the PCB.
The 3 layers are glued together.






The coil is unshielded.
Data:
Weight: 330 g
L: 582 microHenry
R: 18 Ohm


Shaved the edges smooth, glued a couple of ears on, painted it with primer and mounted on my Pickini V4.






PickiniV4 current: 45 mA as opposed to 135 mA with the normal round bundle coil.


Feels very light compared to the normal round coil I use.
Very aerodynamic - if this is even a coil property.


Sensitivity is somewhat less than my normal round coil - which is also a bigger diameter.
Less chatter inside the house.
Still finds a 1 Euro coin at 20-25 cm, which is OK to me for beach hunting. I don't want to dig any deeper anyway.
On the beach I use this one hand - one foot shoveling technique to kick up a shovel of (wet) sand while holding the detector with the other hand.


I plan to do some more real life field tests and come back later to report on performance.

[waltr]

Interesting. Thanks for posting your follow up and congrats on getting this coil packaged and working.
Looking forward to additional field/beach reports.

Very aerodynamic - if this is even a coil property.

lol
If used in the water then 'hydrodynamic'.

[Qiaozhi]

I had 4 of these PCB coils on the shelf for a couple of years now.
Finally had some time during the holidays to turn them into a search coil prototype.
The layout was published here by George : http://www.geotech1.com/forums/attac...5&d=1337436177

Wow!
That's from over 7 years ago -> https://www.geotech1.com/forums/show...004#post150004

[F117]

Yes, this is an old thread.
I kept the link to it until I finally had some spare time to work on this. Thanks George for posting the pcb coil layout in pdf format at the time.

[sinclairuser]

hi bernard, nice coil i have been building and playing with different types, i'm going to post some results soon in my spiral coil tread.
as an aside thanks for the pickini it is a good design and quite tolerant when it comes to the coil, which has been useful for testing these different winds.
hopefully my weekend off will remain free so i can finish my "tinkering".
thanks,
aly.

[F117]

I guess I was quite surprised that this works relatively well considering:
- the small gap in the middel of the circular windings
- the high resistance
- the high inductance

This coil is relatively easy to construct and should give repeatable results.
The mechanical construction is simple and results in a very sexy looking search head.
It is also a fast coil due to very little inter winding capacitance.

So, what should be the obvious disadvantages ?
Has anybody else tried the 2 coils in series setup + mutual inductance ?