Getting ready to build the MPP

[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.

[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

[multieagle]

Thank you, I am using that template.

[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

[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

[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?

[baum7154]

I would use the series diode as it has much lower capacitance that is in series with the much higher capacitance of the mosfet effectively lowering the system capacitance across the coil and raising the Self Resonant Frequency of the coil in the system.
The required damping resistance will then go up according to the formula: PI * Self Resonant Frequency (in mHz) * Coil Inductance (in microhenries) = Rdamping (in ohms)

Regards,

Dan

[multieagle]

Hi multieagle

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

Chet, for some reason I missed reading your reply. Thanks for the info. Have you tried truck bed liner? I use it on my coils. When you notice wear, just apply another coat. Just check that it does not contain conductive material.

[KRinAZ]

Hi all, & apologies for my absence! First time back & enjoyed catching up on this thread.Life takes us in unexpected directions sometimes, I have been (still am) camping at mining claims & prospecting (Chet was so right!). As my internet access is rare & I currently only have my ancient iPhone as a computing device, my posting capability is not so much.I WILL be back to this project again someday! - especially as I really wish I had a working MPP with me with the BWC (basket weave coil). I have been thinking on some mods to the coil design, will build a vacuum table for the coils, & will progress with the MPP. I see it's in revD now, cool.Cheers!

[Chet]

Chet, for some reason I missed reading your reply. Thanks for the info. Have you tried truck bed liner? I use it on my coils. When you notice wear, just apply another coat. Just check that it does not contain conductive material.

Hi multieagle
Thank you, I might give it a try.
Chet

[Achillion]

Did some measurements on the basket weave coil with the following results:

Coil base : 4mm PE 10"x8" oval
Conductor : 0.12 mm2 stranded 26AWG PTFE insulated
Inductance : 338 uH
Capacitance : 31.6 pF
Self Resonance Frequency : 1540 kHz

Planning to replace the IRF740 with an Inineon IPD50R800 and a fast diode (Vishay 5EWH06FNHM3) in series. Front stage to be build in the coil housing.
Mechanical side is also progressing. I used a telescopic carbon monopod from Benro. 3d printed the piece between the rod and coil (through Shapeways).
I want to experiment a bit with the pulse timing and developing this around a LPC 1768 uC (maybe as a future MPP 'shield')
Anyway, lots of ideas to keep me busy.

Cheers,

JCobb

[kellogs]

Hi chet kellogs back on my feet again had some skin cancers taken out of my left leg.any way have been spending some time on the forum and i se a new project has evolved in the mpp i have been on to silverdogs web and he has a revised pcb ;d; i woud like to have a go at building one what are your thoughts mate look forward to hearing from you Kindest Regards kellogs

[Chet]

Hi kellogs

The Minipluse Plus is a good kit. The build manual takes you through the assembly stage by stage. I think you will find it easier than the Surf PI. The coils should be interchangeable. I don't know which is the best machine. Maybe someone on the forum knows which has the best performance.

I wish you a fast recovery and have a great day,
Chet

[baum7154]

Did some measurements on the basket weave coil with the following results:

Coil base : 4mm PE 10"x8" oval
Conductor : 0.12 mm2 stranded 26AWG PTFE insulated
Inductance : 338 uH
Capacitance : 31.6 pF
Self Resonance Frequency : 1540 kHz

Planning to replace the IRF740 with an Inineon IPD50R800 and a fast diode (Vishay 5EWH06FNHM3) in series. Front stage to be build in the coil housing.
Mechanical side is also progressing. I used a telescopic carbon monopod from Benro. 3d printed the piece between the rod and coil (through Shapeways).
I want to experiment a bit with the pulse timing and developing this around a LPC 1768 uC (maybe as a future MPP 'shield')
Anyway, lots of ideas to keep me busy.

Cheers,

JCobb

--------------------------------------
What is your self resonant frequency with 36" of feed line? Depending on what feed line is used I would expect the SRF to drop to 1.050 mHz or so which is right about where all of my 300 uh to 335 uh spider coils end up with feeds. However once they are in circuit on my CHANCE PI they really end up at about an SRF of about 850 to 950 kHz.

Regarding the Infineon IPD50R800 it looks like the device has a COSS of about 400pf at 12 volts (DSS) but they show it has 23pf @ 100 volts Drain to Source. Is that better than the IRF 740?

Regards,

Dan

[kellogs]

Hi chet once again thanks for your help i will be ordering a kit from silverdog also where do purchase the chance pi from my next project is to build your oval coil grat to hear from you have a great day Kindest Regards kellogs.