Getting ready to build the MPP

[johnandles]

I have an idea for name - more practical than flashy ...... I believe make stick on vinyl decals from an image...

OB1 (oval basket 1)...may the force be with you...
lol

[Silver Dollar]

BWM800 and BWM810 for Basket Weave Mono 8" & 8"x10",

I got the shoes;

I would a 10" coil with the Litz tonight. I'll test it out tomorrow or Saturday..


I found some MUR460's in old TV sets. I'm planning on using those...

[KRinAZ]

Question on that high speed, high voltage diode used to lower TX circuit resonant frequency - if someone didn't have any diodes on hand and was going to get some diodes specifically for this - would the MUR460 be recommended or is there another diode that would be even better/faster?

[KRinAZ]

I have an idea for name - more practical than flashy - BWM800 and BWM810 for Basket Weave Mono 8" & 8"x10", can put the flashy in the graphics...folks like SharpDots.com (I have no affiliation with them) and maybe even the local office supply stores with business printing capability can I believe make stick on vinyl decals from an image...

[KRinAZ]

Hi KRinAZ, do you have a plan for a coil housing for your new oval coil? I haven't worked with Lexan. Do you think it would work for a housing?
Hey Chet, yes, I do have a plan! I've discussed this coil with Don Bowers and suggested that if a number of us build these coils and would like a housing he could make housings for us. Currently it looks like the housing would be about 8.25" x 10.25" x 1", could be any mount we all agree on (he usually uses the 19mm Whites/Tesoro/Minelab mount tabs unless otherwise specified) We will need to get the cost per housing from him when we are ready, it appears they would be around $15 each (US Dollars) - price seems good to me!
On the Lexan, it seems to be pretty heat resistant and not as well suited to heat/vacuum forming as ABS. Don uses ABS sheets, can be either black or white, I'm told black is UV resistant, white is not.

If we have some made I can make a cool graphic to stick on top of it! Name for the coil, anyone?

.

[KRinAZ]

To rehash the template discussions, seems like pretty much everyone has run into problems with the wire slot width, in my case the inner slots becoming filled faster than the outer. I will make a revised version of the template with the inner slots at .55" depth, leaving the outer slots as they are at .4" depth - as on my builds the outers are still anchored well where the inners are just past their limit - I believe this should yield a coil that is equally balanced for anchoring on inner and outer slots.

The next set of templates will be hopefully posted this eve...

[KRinAZ]

Hi KRinAZ, when I built mine I didn't even think to check the DC voltages on TP3. The scope is the way to go on most checks. Looks like you are well on the way to completing yours. The coils are very sensitive to any metal in the work area. Two solutions for this. Suspend the coil by cord from the ceiling away from the bench, or place it on a plastic wastebasket on the floor away from the bench. Hi Chet, thx for that tip.

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?

Great job on the new coil. Looks like for others using your template that it should be a little greater in width and the slots should be a little deeper. Yes, on the two coils I've built I've found the inner slots get crowded faster than the outer slots - cut the same width - the outers can take at least 2 more turns than the inners. I think the ring width may be OK but the inner slots could be cut .5" instead of.4". This would also move the coil out slightly. The Lexan is definitely strong enough to handle the deeper cuts. One reason my builds are getting crowded on the inner slots is because I'm using up this super fat wire that I won't get more of. Something like Silver Dollars .9mm Litz (my wire is approaching twice that diameter) would fit no problem, I believe.

This would help on the inside turns to keep them anchored better. I had a problem with this and it looked like baum7154 had a similar problem with his coil. Yes, I agree, I had this issue also, from my builds I would say if someone is using a wire with OD of 1mm or greater it would benefit to cut the inner slots to .5", or if more turns are desired and/or with 1mm or greater wire maybe cut both slots deeper, keeping the inner slot depth at least 2 wire OD widths deeper than the outer.

.

[KRinAZ]

I seem remember commenting on this point some time ago. Just go ahead with the build. The voltage measurements I wrote in the Build Document for Step 5 were based on a single build, and I did [subsequently] find that these numberes varied between different units. The main point is to confirm that the voltage level changes when metal is placed close to the coil.
Oh good, many thanks Qiaozhi, I will proceed with the build then.

.

[KRinAZ]

Neat.
My coil is not nearly as neat, and I'm not able to hook it up at this point, but I figured out a small detail that may save people a few long rows of cursing: I marked an outer lead with a water resistant marker. That particular wire is also used as a shield in this particular configuration, so it is kinda good to know which is which
Thx! & yes I completely agree and I mark the outer wire also (forgot to mention that) and use it as the 0V connection - like you and others I've also found it's important to connect it that way - for the self shielding to work

.

[KRinAZ]

Look here for a lot of scope shots of my receintly completed Hammer Head; http://www.geotech1.com/forums/showt...s-best-Damping
Excellent, many thanks Silver Dollar!

.

[Chet]

Hi KRinAZ, do you have a plan for a coil housing for your new oval coil? I haven't worked with Lexan. Do you think it would work for a housing?

[Chet]

Hi KRinAZ, when I built mine I didn't even think to check the DC voltages on TP3. The scope is the way to go on most checks. Looks like you are well on the way to completing yours. The coils are very sensitive to any metal in the work area. Two solutions for this. Suspend the coil by cord from the ceiling away from the bench, or place it on a plastic wastebasket on the floor away from the bench.

I measured a 4' length of twisted # 22 Teflon wires with thinner insulation than yours. It measured 39pf on the capacitance meter.

Great job on the new coil. Looks like for others using your template that it should be a little greater in width and the slots should be a little deeper. This would help on the inside turns to keep them anchored better. I had a problem with this and it looked like baum7154 had a similar problem with his coil.

[Qiaozhi]

If anyone has some checks or ideas I would sure love to hear them!

I seem remember commenting on this point some time ago. Just go ahead with the build. The voltage measurements I wrote in the Build Document for Step 5 were based on a single build, and I did [subsequently] find that these numberes varied between different units. The main point is to confirm that the voltage level changes when metal is placed close to the coil.

[Davor]

Neat.
My coil is not nearly as neat, and I'm not able to hook it up at this point, but I figured out a small detail that may save people a few long rows of cursing: I marked an outer lead with a water resistant marker. That particular wire is also used as a shield in this particular configuration, so it is kinda good to know which is which

[KRinAZ]

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:



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.


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!