28ga teflon wire

[Andi68]

Divide the number of windings in layers, since no basket coil can keep up

[green]

Here is a double-sided spiral I did in Easy-PC between code compiles:

[ATTACH]43710[/ATTACH]

It has 60 mil traces with 25 mil spacing, N=24, d(nominal) = 10" (25cm). I chose trace width/spacing to keep the overall ring @ 1" wide. With 2 oz copper the trace width is equivalent to ~27 AWG so the "gauge" and spacing are almost the same as the OP's specs. It would be interesting to compare results.

PCBWay quotes $209 (plus shipping) for 10 boards, so right now it's a little pricey to find out. It's something I've been wanting to play with for some work projects so I may do it anyway. Obviously you don't want to waste all that middle real estate so maybe make it a set of progressively smaller coils.

Hi Carl, reply #15 you mentioned double sided. Was thinking the two sides in parallel for lower resistance. The picture shows 12T on a side for 24T coil. How do you connect them in series(inside, outside or inside to outside)? A comparison with a spiral wrapped coil would be interesting. AWG28 solid wire is detectable, would the flat trace be more or less detectable?

[dbanner]

Here is a double-sided spiral I did in Easy-PC between code compiles:

[ATTACH]43710[/ATTACH]

It has 60 mil traces with 25 mil spacing, N=24, d(nominal) = 10" (25cm). I chose trace width/spacing to keep the overall ring @ 1" wide. With 2 oz copper the trace width is equivalent to ~27 AWG so the "gauge" and spacing are almost the same as the OP's specs. It would be interesting to compare results.

PCBWay quotes $209 (plus shipping) for 10 boards, so right now it's a little pricey to find out. It's something I've been wanting to play with for some work projects so I may do it anyway. Obviously you don't want to waste all that middle real estate so maybe make it a set of progressively smaller coils.

Maybe put pattern of one of the smaller coils for dual Field option. I assume you will have them cut and separated individually.

[Carl-NC]

I think it'll be fine.

[RobN]

Thanks 6666 I will give it a try.

[RobN]

Wow thanks Carl. I figured about 5 or 6 more turns to get somewhere between 325 to 350.
What do you think about the resistance? Is it going to end up to be to high? Already at 3.3 ohms.
It’s getting a little high don;t you think?
I’m beginning to think I’m wasting my time on this one. But you don’t know the answers until you try Right? Experimentation is what it’s all about!

[Carl-NC]

[ATTACH]43711[/ATTACH]
I ran out of wire on this one length of wire that I had, I have more so I am going to try and splice on some. I am at 28 turns and according to the coil calculator I used I needed 29. At 28 turns I am at 225 uH and about 10.8 uF and 3.3 ohms. Any guesses how many more turns I need to get to around 350 uH? I included a picture if it worked.

Generally, 225uH/28^2 = 350uH/N^2, so N=35. 7 more turns. However, the SMPI is pretty tolerant and will likely work with 225uH. The stock coil for the White's is 250uH.

[6666]

Wire plus insulation? If so how would I apply the gap between wires? Just add zero gap?

yes and yes, try it and see what it calcs vs what you measure I assume you have an inductance meter.
I haven't found any of those spiral coil calcs to be much good.

[RobN]

Wire plus insulation? If so how would I apply the gap between wires? Just add zero gap?

[6666]

I have noticed from using this wire in the past that the inductance runs lower than what the coil calculator come up with.

Try using the outside dia of the wire as the wire size in the clac and see what it gives

[RobN]

I think that once I get enough turns on here to get the inductance up where it needs to be that the resistance will be to high to be any good. What would be the perfect inductance for a Surf PI? And what would be the highest the resistance can be before it’s useless?
I think it needs to be done with a bigger gauge wire to lower the resistance. 28 gauge is just to small. And the teflon coated silver plated wire is to expensive to experiment with. I think I paid somewhere between $25 to $30 for a 100 foot roll of this stuff.
Would it be worth the time to make a flat spiral coil out of PVC copper stranded wire of a bigger gauge? I will have to try and compare them together. I’m going to have to make a basket coil jig as well. Back a couple years ago I made a coil from speaker wire for a surf PI and it seem to work great before the surf PI quit on me, not sure why it did if it was the speaker wire coil that caused it or what but just trashed it and gave up MD for a while and didn’t really know what I was doing back then. Now I’m getting back into it and by reading all the post out here I learned a bunch and since got a Oscope. So keep up all the good post and I will keeep learning. Sorry for the long post. Hope you all find a treasure. Thanks all, Rob.

[RobN]

I have noticed from using this wire in the past that the inductance runs lower than what the coil calculator come up with.

[RobN]

I ran out of wire on this one length of wire that I had, I have more so I am going to try and splice on some. I am at 28 turns and according to the coil calculator I used I needed 29. At 28 turns I am at 225 uH and about 10.8 uF and 3.3 ohms. Any guesses how many more turns I need to get to around 350 uH? I included a picture if it worked.

[Carl-NC]

Rob, you're looking at about 3.7 ohms for the coil resistance. A tad high but not worth doubling or tripling the wire. If the TX is 100us you'll go from (ideally) 2.1A to 2.9A by tripling the wire; the benefit diminishes as the TX gets shorter. Also, additional gap between the wire probably won't buy you noticeable speed, but probably will noticeably reduce TX efficiency.

[RobN]

I have considered twisting 2 or 3 strands together but this teflon wire is not cheap and I don’t think I would have enough wire to do it. I made a couple of bundle coils with this teflon wire a couple years ago but my MD crapped out before I had the chance to try them out and kinda got out of the MD’s for a while. I have recently found a surf PI kit in my junk collection and I am just finishing putting it together. I took the teflon wire out of one of the bundle coils I made and was wanting to use either a flat spiral or a basket coil out of it to use on the surf. The problem is in order to make it I would most likely make in a Permanent state and wouldn’t be able to reuse the wire again kind of a do or die thing. That’s why I was looking for other opinions and I thank you all for them. I’m going to make the flat spiral trying to decide on spacing or not between the wires. I will just make it and see what happens.