Competition!

[August]

"I can't get litz. Except me to looking for power cables, but the "channels" in the enclosure are so tight that the PVC litz won't fit there, as many windings as I think I'll need.
Question; would it change anything if I wind bifilar with 0.3mm? Or should I take 4 x 0.15mm? Or similar?"

Hello.
It is possible to use any wire diameter. It is also possible to combine wires with different diameters to achieve the required resistance and inductance for a given number of turns.

[Xtrem]

ivconic , what you dont know are the turns from the original coil, if you make more turns you lost the smaller targets ,
test the original coil with different targets, small medium bigger , it is response the same? (30% better)?
Bifilar winding would increase the capacitance of the coil at the same turns, same wire.

[GeoMax]

Hi August,

for what detector electronic do you want to make a coil?

[August]

Hello GeoMax.
I was answering Ivconic, to his question

[Op04]

Since Sir Invconic bring this "complicated" question, That is what I need to know also...but I want to add a question: Does increasing frequency or PPS will also increase Ampere Turn?

[MDfanatic]

What we really need is not a competition but a coalition of members so we can come up with a new design for a DIY machine and ignite the interest of on-lookers, new-comers and old-timers in the hobby.

I liked the idea of Felezjoo PI and the involvement of so many users to build, test and troubleshoot the design, we could do something similar and maybe we can come up with something new and unique.
No matter how big or small the partitipation will be, all members could benefit from the knowledge and especially new-comers to electronics like me.

Count me in, I hope I can contribute in any way I can and learn along the way.

[ivconic]

[Carl-NC]

Does increasing frequency or PPS will also increase Ampere Turn?

No, but it does increase the integration rate which improves SNR.

[profesor]

Square wave VLF detectors that I am working on.
minelab explorer. fisher cz 70. whites spectra.
etc
All tx coils were litz wire.

[pito]

Where is the button - start new topic ?

[Op04]

No, but it does increase the integration rate which improves SNR.

Thanks for the answer Sir, so in my mind, we must keep number turn a lot more but still catch up with coil TX On , but again we need the current flow quite enough current to meet deeper detection and when use high AWG number the coil will not survive if applied with high current as we want more turn then we need resistor, what confusing is in the TDI on the old one and newer version the damp is differ, the newer use 580 ohm while the old version using 680 ohm vs each using differ voltage but both version can use the same minelab coil now that's need a lot explanation. Since Ivconic bring this question, I think we need more spesific answer. Why do commercial coil always have successful build with all different damping and voltage? Making with litz is hefty price. So when build DIY coil we must take carefully damping differently? for the same machine vs commercial one.

[bbsailor]

Joseph, it's good to have you here, you rarely appear, you don't write often... but you always write good and useful things.
Maybe this is off topic... I have a dilemma, your opinion would help and mean a lot to me.
I make copies of Pulse Star 2 (analog version). Not that often, maybe once or twice a year. I work with the detector until it is sold.
I am not aggressive about advertising and selling that detector. The initial motive for making it was for personal use.
That's why I didn't bother to establish one and the same coil for it. I usually make a coil from currently available material.
If you've ever seen a PS2 (either analog or digital "Pro" version); you must have noticed that there is a switch for Sample Delay on the front panel, with 4 positions.
Position "1" is the shortest delay. And 90% of the time I use the detector like that. And the coils that I have made so far were generally from 18cm to 42cm in diameter.
Not because I intended it to be; but because I mostly found such coil "cases" (lids made of plastic bins and similar handy material).
With the 18cm coil detector works almost unbelievably well! With such a small coil diameter; the ranges are incredible.
The 18cm coil has an inductance of ~380mH and a resistance of no more than 3 ohms. Damper at it is 680 ohms.
But as I increase the coil diameter; thus the detection results decrease. It's still good, but not as "sensational" as with 18cm.
Some time ago I acquired (from a friend from another country) 3 coil enclosures with 56cm diameter.
And since then I've been trying to make a good coil for those cases/enclosures. Alas... I fail. I tried with wires 1mm, 0.8mm, 0.5mm and now almost with 0.55mm.
I use regular Cu wire. No litz, because I can't find it.
I am "chasing" the inductance of 0.68mH-0.7mH because it is that much on the original PS2 45cm coil. And resistance no higher than 2 ohms.
Apparently, a 0.6mm wire would be suitable, which I don't have now but plan to get.
But even with 0.55mm I got very close specs. But the detection is still not "sensational". But very average.
I have in my place a friend with the original PS2 Pro with a 45cm coil. When I compare; the original works at least 30% better.
And someone recently mentioned to me in a conversation that he knows for sure that the original is wound with litz.
I still don't know the damper value in the original.
But the value of that resistance is not a problem, it will be established by observing the RX signal on oscilloscope and using a "jig" to adjust. (potentiometer and resistor in parallel with the resistor)
Somehow I feel in advance that even with a 0.6mm wire I will not be happy.
I can't get litz. Except me to looking for power cables, but the "channels" in the enclosure are so tight that the PVC litz won't fit there, as many windings as I think I'll need.
Question; would it change anything if I wind bifilar with 0.3mm? Or should I take 4 x 0.15mm? Or similar?
How many wires in the litz are actually necessary to achieve an effect similar to the original coil? (A similar question applies to all ML coils).
What most of us declaratively know; it is that litz is always better than single wire. But few of us understand all aspects of that story.
And so far, I haven't found anywhere that anyone has done experiments with "multi-filar" attempts, not from originally purchased litz, but from hand-prepared wire.
I would like to hear the opinion of someone who knows it much better than I do.
Thanks in advance to you and to anyone else who would know what to say on this topic.

Making pulse induction coils is always a compromising situation. Coil diameter or square size affects what target metal type and depth it can detect. Wire diameter and wire type being stranded, solid or insulated strands can affect the detecting outcome.

Get familiar with the AWG wire table and the column that specifies the maximum frequency for 100 percent skin depth. Pulse induction metal detectors have a wide range of operating pulse frequencies and will initially point to an appropriate wire type and diameter. If you are seeking small targets you will need to reduce the delay from the transition of the TX pulse mode to the RX mode. However, if you are using thicker solid wire for a coil, the wire itself may look like a target at low delays. This is why learning how to use the AWG wire table to form a good mental model of wire sizes, skin effect frequencies and ability to use a chosen wire for a coil.

The Pulse Star 2 operates at 611 HZ. AWG 4 has a maximum skin depth frequency of 650 HZ with a diameter of 5.8922 mm. If the AWG solid wire is seen as a target, it means that either a smaller wire is needed or a stranded wire which will not look like a target. Where the stranded coil wire is soldered and connected to coax cable, that joint may look like a target at low delays.

The AWG wire table can be used to plan for selecting your wire sizes to try. Here is an example that I discovered when researching for my Fastcoil.pdf article. AWG 30 has a diameter of .254 mm or .01 inch with an area of .0509 mm squared. Drop the wire gauge by 3 sizes to AWG 27 with a diameter of .36068 mm and an area of .102 mm squared and you will have a wire very near half the resistance when going lower or about twice the resistance when going up 3 sizes to AWG 33. Remember this as a good mental model when selecting a wire gauge for your coil.

It would be very convenient if there were just one thing you could do to make a fast coil but there are many things that collectively push the coil performance in the same direction. These include:
1. Wire gauge
2. Wire style, solid, stranded, Litz wire
3. Insulation thickness of coil wire
4. Dielectric constant of chosen wire insulation and spiral wrap around coil winding
5. Compactness of coil wound bundle to fit coil housing space
6. Coil seen capacitance that needs to be damped
6.1 Coil turn to turn capacitance
6.2 Coil to shield capacitance
6.3 MOSFET coil driver capacitance
7. First amplifier stage gain, speed of response and noise
8. Coax cable connecting coil to control box

When making coils and properly damping them to your metal detector take good measurements of the following on the coil alone.

1. Coil inductance. When using thicker wire insulation, the wire strands will be spaced farther apart thus lowering the inductance requiring extra turns to meet your desired coil inductance.

2. As you build your coil the resonance of the coil will change from the raw wire coil on the coil form. It will go lower when the first layer of spiral wrap is added and lower when a second layer is added. Adding the shield will also cause the coil self resonance to go lower. Set up your signal generator to stimulate the coil through a 1 meg ohm resistor to allow the resonant point to be easily seen on an oscilloscope. Put a 1 pf capacitor in series between to coil and the oscilloscope to not load down the resonant point. Once you know the coil inductance you can add the observed resonant peak to the coil inductance and calculate the capacitance in the coil and coax. Keeping track of the damping resistor value will reveal how much capacitance the coil sees while wired to the pulse induction circuit.

3. When you make many coils and do my suggested measurements, you will sometimes reach situations where variables start to work in opposite directions and require some compromises. The advantage in doing low volume custom coils is that you can take the time to move as many variables in the same direction to get the final performance that you seek.

True learning means extracting knowledge from your experience and seeing connections between variables. Coil building has a lot of this!

Joseph J. Rogowski

[Tinkerer]

The next best thing after genuine Litz wire, is to use fine strand tinned wire. Like 600V AWG 20 1x19 . This is much cheaper.

[ivconic]

Joseph, your posts are always "condensed" ie. with few words you always say a lot of interesting things.
I'll have to save that post to a document and read it over and over again. As a kind of reminder. Thank you very much!
What to say?
A good explanation always helps a lot.
The 56cm coil is certainly not intended for hunting targets with low TC.
I don't think there is any fear of the detector seeing a piece of wire as a target in that case.
I certainly don't expect to successfully hunt for individual coins with a 56cm coil.
But objects the size of a typical PC power supply are likely to be a common target for such a coil.
Even the original 45cm coil is not perfect for coins.
But it definitely works better on larger targets than the coil I tried to make.
All I'm trying to do is match the performance of my 56cm coil to the original 45cm.
It is obvious that the difference is precisely in the type of wire used in the original coil.
Tony maybe I'll try just that first.
My English vocabulary is poor, I always forget the right term, when I often mentioned "PVC litz" - I actually meant "stranded" wire.
But I have to find a thinner "bundle" because the "channel" in the plastic case is the limiting factor, there is not enough space for thicker bundles.
We'll see, I have 3 enclosures. It would be nice to make 3 good coils.

[Carl-NC]

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