Getting ready to build the MPP

[Boadil]

Aside from my Step5 prob's, something did go well this eve - behold! - I couldn't resist and made a basket weave 8x10 coil from the template previously posted.

Specs:
32 turns (6 layers plus 2 more turns) 26AWG stranded Teflon coated 600V wire
324uH
3.0 ohms
Capacitance unknown as I won't calc it until I have put a fast diode in series with the coil. Resonant freq without any diode was 454.5K, I experimented with (Chet suggested trying a high speed high voltage diode, which I will need to get) a 100V 10uS diode (too slow and too low reverse voltage but the magic smoke stayed in the diode) and the resonant freq went up to 833K, I'm guessing it will go up higher when a fast diode like the suggested MUR460 is used. Also it is still damped by the 470ohm R1, I need to find the correct damping resistor value once the diode is in place.

Pics of the build and coil:
[ATTACH]31571[/ATTACH]
[ATTACH]31572[/ATTACH]
[ATTACH]31573[/ATTACH]
I drilled holes at each end of the wire cutout this time to make sure the slots are deep enough, then cut them with jigsaw (this is actually the method baum7154 suggested), then cleaned up the cuts with the 1/8" bit on the Dremel - this worked much better and faster for me.
[ATTACH]31574[/ATTACH]
[ATTACH]31575[/ATTACH]
I am hoping this coil works out well, can't wait find out it's capacitance, and try it out when the MPP is ready for field tests!

that use diode in the end?
that result has been, could you tell me the reference of this?

[Chet]

Chet, let me know how it works out. I have dealt with Don and he is a straight shooter. Should have my oval coil finished this coming week. So will be in the market for a shell.

Gord

Hi multieagle

I am very pleased with the quick response and the work that Don did. He built the housings with higher clearance within an hour of my request. I received them in a few days.

In my order he had standard forms already built. In your case he doesn't have oval coil forms built for the Basket Weave template. So there will probably be added cost and time involved. You should contact him since there may not be many ordering this form.

Also you might ask if he can use a thicker ABS material or can provide skid plates. I think I will wear through the bottom of my coil housing quite quickly. The California gold areas are much harsher than grass in the parks. I go through at least one skid plate each year.

Regards,
Chet

[multieagle]

I think KRinAZ is off digging gold so I just ordered to round Clam Shell coil housings from Don Bowers. He is increasing the inside height to accommodate the fatter winding of the Basket Weave coil.
Chet

Chet, let me know how it works out. I have dealt with Don and he is a straight shooter. Should have my oval coil finished this coming week. So will be in the market for a shell.

Gord

[multieagle]

Thank you, I am using that template.

[Chet]

In process of putting together the oval basket weave coil. I have some surplus wire rolls, 175/46 (0.04 mm) Litz Wire, single layer nylon insulation, 0.90 mm diameter and 24AWG enamal insulated single core magnetic wire. I'm leaning toward the Litz. For this 8x10" design, what would be the estimated turns for approx. 300-325uH result?

Hi multieagle the following is from KRinAZ in Post#88 of this thread;

"I have updated the basket weave coil templates for the increase in the inner wire slot depths from .4" to .55" to balance the wire anchoring in the slots. I have also added a version number to the templates in the lower right corner so you can know if you have the latest. The latest 8"x10" elliptical is v5, the latest 8" round is v2.


8 inch Coil Form v2.pdf
8" Round v2
8x10 Coil Form v5.pdf
8"x10" Ellipse v5


These are intended to be used with 32 turns (6 layers + 2 turns) (or less) of wire with OD up to 1.5mm, yielding about 324uH and around 3 ohms at 32 turns, depending on the wire you use. Smaller OD wire will allow even more turns and higher inductance.


As always, let me know if you discover any issues with these templates, and enjoy!"


I suggest starting with enough wire to add several more turns especially if you use Litz wire since it is harder to splice if you come up short.

If you have an inductance meter you can measure the inductance after you get 32 turns wound. Just stretch the extra wire out away from the coil and loop the end back so you can measure the two ends with your meter. This way the extra wire will have little effect on the measurement. From there you can add a few more windings and measure again.

If you plan on using twisted pair to reach the detector box; leave enough wire from the start winding point to reach the detector and extra wire at the end of winding to reach the detector.

If you use Litz twisted pair it will need to be encased in flexible tubing for protection.

Regards,
Chet

[6666]

Thats a tough one as these basket weave spider coils take more wire than a bundle coil, both dan and I have wound the 8 inch with different wire but ended up with almost the same values 32-33 turns gave around 325 uH, i used cat 5 wire, stranded copper 7x.2mm with polypropylene insulation, you can see my coil in the chance coil thread,my next project is the 8x10.

[multieagle]

Hi KRinAZ, from post #75; “I measured a 4' length of twisted # 22 Teflon wires with thinner insulation than yours. It measured 39pf on the capacitance meter. Good to know - think there's any coax that would be lower in capacitance?”


I use Blue Jeans LC-1 Audio Cable at 12.2 pF/ft, it gets close to matching twisted pairs. It is very durable and handles better than twisted wires. And it looks better. If you plan on making a number of coils it is cheaper to buy one long cable and cut to length as you use it. Just toss the two connectors that come already attached.


http://www.bluejeanscable.com/store/audio/

In process of putting together the oval basket weave coil. I have some surplus wire rolls, 175/46 (0.04 mm) Litz Wire, single layer nylon insulation, 0.90 mm diameter and 24AWG enamal insulated single core magnetic wire. I'm leaning toward the Litz. For this 8x10" design, what would be the estimated turns for approx. 300-325uH result?

[baum7154]

You are very patient and persistent to have drilled all those holes and then threaded all that length through them! If I counted right it looks like you did about 30 turns on the form. The holes indeed help separation of the wires and should help keep capacitance lower. What voltage rating is the PTFE insulation of the wire? It will be interesting to see what the Self Resonant Frequency of this coil measures. Goooooood job!

Regards,

Dan

[multieagle]

Great looking coil. Must have been murder drawing upwards of a 100' of wire through each hole! Will follow to see how it reacts in actual use.

[Achillion]

Pictures of basket weave oval coil and housing.

[Achillion]

Established a working MPP

Since this is my first post I believe it is appropriate to introduce myself briefly. My name is Jacob, I’m Dutch but now living in North Queensland, Australia. I’m interested in the electronics side of metal detecting and that’s how I ended up at this site. I’m member of the local metal detecting club and my aim is to build my own PI gold detector with performance that can compete with commercial detectors.

I just completed the Mini Pulse Plus and will use this design as the base platform trying to further develop and improve, which was the intention of the MPP project (all credits to Qiaozhi and others who initiated this project).

My approach is to focus on each of the building blocks individually and see if there opportunities for improvement. I read post of the many bright people here on this forum which helped me a lot. I hope I'm able to contribute also.

As a first step I focused on the search coil design and build the Oval Basket Weave coil with some slight modifications. Still experimenting with various other designs also. Along the way I crafted vacuum mold table to make a suitable housing. I’m able to detect a square cm aluminum (coke can) at about 0.5 inch with the basic MPP.

I used a 4mm PE base with 0.12mm2 26AWG PTFE insulated silver plated stranded occ copper. Instead of slots I drilled holes to maintain separation at the crossings. I’m not sure though if this is the optimal design to lower parasitic capacitance. Will post some photo’s once I know how to.

Cheers,
Jacob

[jladre]

Thank you Silver Dollar and baum7154 for the explanation..now im gonna ground it)

[baum7154]

Thank you for the answer..will it just my opinion to draw more power because the aluminum box may consume a little power from the battery..im just a newbie in electronics and need much knowledge..

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The only effect you will see from grounding the metal box is better performance because of the RF/EMI shielding it will provide.

Dan

[Silver Dollar]

Darn I ordered parts mainly to get the LT1054 and I ordered the wrong one!
It has 16 SMT pins not 8 pin DIP. I geuss I'll have to fudge it in...

[Silver Dollar]

Well Santa brought me all the parts to build this MD so I'm ready to start building!

The aluminum box will not use any power. You need 2 contacts for power to run through.
There might be a little loss as it acts as a capacitor a little...