28ga teflon wire

[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.

[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!

[RobN]

Thanks 6666 I will give it a try.

[Carl-NC]

I think it'll be fine.

[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.

[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?

[Andi68]

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

[dbanner]

I think maybe the thickness of PCB board may slightly reduce inductance of overall dual printed coil, may need to add a couple of turns to compensate.
Curious to know what the measured inductance and SRF turn out to be.
It deserves its own thread.

[nonkapo]

Was checking avaiability of the PCB boards - most of them come rectangular. Very few suppliers offer 30x30cm which i gues will be the best size to start from. Also very few offer double sided boards sqare type.

[dbanner]

Was checking avaiability of the PCB boards - most of them come rectangular. Very few suppliers offer 30x30cm which i gues will be the best size to start from. Also very few offer double sided boards sqare type.

The only downside to this printed coil design is going to be the cost. In most cases It will be more expensive than the detector itself. For home builders of surf, bara minipulse etc. It will be very expensive. A less expensive option would be to just go with single layer spiral.

[green]

Hi all, I am planning on building a flat spiral coil from 28ga. Silver plated stranded teflon coated wire. The wire specs are .0275 inch with insulation and all. Wire dia. Without insulation is .0145in which would leave a total thickness of .013 for the insulation. This is all measured with digital calipers and not by the data sheet of the wire.
i am going with a ID of 6.75” (just a piece of round plastic I had on hand to use as a die) and according to the flat spiral calculator I am using- 6.75”ID & 29 turns & wire dia of .0145 with spacing of .013 between each wire would be—
Inductance of 351.965uH
OD of coil 8.345”
total wire length of 687.623” (doesn’t show ohms) I will try other coil calculators to see what they say later. For now I just want some of your all opinions if this is even doable.
would this be usable for a Surf PI 1.2 (from what i have read on this forum for a surf PI the inductance should be between 300 to 350) please correct me if i’m Wrong.
Should I have bigger spacing between the wires?
Is the wire just to small to be useful.
I can add some small string between the wires to space them out more if needed.
Please any advise will be very, very helpful.

Have you finished the coil? Interested in how Teflon coated wire compares with magnet wire.

[Qiaozhi]

The only downside to this printed coil design is going to be the cost. In most cases It will be more expensive than the detector itself. For home builders of surf, bara minipulse etc. It will be very expensive. A less expensive option would be to just go with single layer spiral.

If you have access to a CNC machine, you could engrave an SRBP copper clad board as a much cheaper alternative.

[green]

I'm just trying to learn. Have read spiral coil is fast but adding shield makes it slower than other winding methods, not what I've found. Most of the time I have more questions than answers. I don't know why the overshoot, looking like the coil is underdamped or why the overshoot is different between the two coils. The flat spiral has a lower circuit resonance maybe some of the reason.

Added lead length and Tx circuit capacitance are higher than coil capacitance.

Reason shielding didn't make it slower. I check resonance by exciting an operating PI with the test coil(hold it near operating PI coil)with scope connected to operating PI amplifier out. I connected the shield to circuit common instead of one of the test coil leads like I should have(test coil isn't connected to circuit common when checking for coil resonance, wasn't thinking). Including scope pictures of some repeat tests I did today. Wondering if I'm doing something else wrong. Picture flat radial_2 is where shield was connected to circuit common instead of one of the test coil leads. Added some scope pictures with test coils connected to Tx driver with and without a series diode(scope probe clipped to coil lead insulation to minimize added capacitance to the circuit). I calculate coil inductance by adding a capacitor across the test coil when checking for coil resonance. The 100nf capacitor measures 100.0nf on my better meter and 97.5nf on the other meter. The 10nf capacitor measures 10.4nf on both meters.

[6666]

Reason shielding didn't make it slower. I check resonance by exciting an operating PI with the test coil(hold it near operating PI coil)with scope connected to operating PI amplifier out. I connected the shield to circuit common instead of one of the test coil leads like I should have(test coil isn't connected to circuit common when checking for coil resonance, wasn't thinking). Including scope pictures of some repeat tests I did today. Wondering if I'm doing something else wrong. Picture flat radial_2 is where shield was connected to circuit common instead of one of the test coil leads. Added some scope pictures with test coils connected to Tx driver with and without a series diode(scope probe clipped to coil lead insulation to minimize added capacitance to the circuit). I calculate coil inductance by adding a capacitor across the test coil when checking for coil resonance. The 100nf capacitor measures 100.0nf on my better meter and 97.5nf on the other meter. The 10nf capacitor measures 10.4nf on both meters.

How many toothpicks do you use in your basket coil , thanks.

[RobN]

I have not finished the spiral coil with Teflon wire yet. My wire came up about 4 or 5 wraps to short and I have to solder another length of wire to it. Right now I am at 28 turns it's 250uH and at 3.3 ohms. Resistance is getting a little high ben better with larger dia. wire. Try to get back to it in a day or two.