Litz wire - what to get?

[bklein]

Ok, I'm a dummy when it comes to this stuff. I go on ebay and I see a wide variety of choices - thin wire many strands, thicker wire less strands.
If you were to build specifically a PI coil for TX what to buy?
If you were to build specifically a PI coil for RX what to buy?
If it matters, I am not interested in maximizing depth beyond 15" or so. I 'm too lazy
to dig for hairpins that deep. But I would like to find gold widgets that are said to escape the normal coil designs. I am interested in treating the coil requirements separately for TX and RX - optimizing each function and then deciding what to do to combine best of both. So if a TX pulse would fry a RX coil with thin wires etc. don't worry about that - just say what you think would be best for each function. In fact, don't even worry about battery current draw. Maybe I'll use a supercapacitor backed source with rechargeable Lipoly... I have some nice 5AH ones!

Barry

[chemelec]

I wouldn't recommend you using LITZ wire for a VLF type Coil.

NOT UNLESS YOU HAVE A LOT OF EXPERIENCE IN COIL WINDING.

[bklein]

Well, lets say one has that (no I don't). Do you look for wire with the most strands or compromize somewhere. Minelab feels it is worth spending extra money on, right? What spec Litz wire do they use? If I have to spend money on this to experiment I want to start with the knowns rather than coin flips.

Barry

[chemelec]

Well, lets say one has that (no I don't). Do you look for wire with the most strands or compromize somewhere. Minelab feels it is worth spending extra money on, right? What spec Litz wire do they use? If I have to spend money on this to experiment I want to start with the knowns rather than coin flips.

Barry

For Performance, More strands should be Better.
But to be Practical, Considering a VLF detector uses fairly small wire to start with, there are limitations

Possibly a 30 AWG Litz Wire, with Single Served Insulation with 10 of 40AWG, Multi-Strands.
And Litz wire will make a physically Heavier Coil.

As to Minelabs coils, I have NO IDEA What they use!

[mario]

Well, lets say one has that (no I don't). Do you look for wire with the most strands or compromize somewhere. Minelab feels it is worth spending extra money on, right? What spec Litz wire do they use? If I have to spend money on this to experiment I want to start with the knowns rather than coin flips.

Barry

Litz wire is very difficult to use if you don't have good experience. It's also very expensive. Usually, 30-50 $US will get you through only 1 -2 coils. And, if you don't have much experience winding, often times, you will not even be able make one good coil. For instance, if you cut prematurely, and are using 30 Strands 31 AWG litz, how are you going to solder back the 30 individual strands back to the main winding successfully?

Also, generally speaking, the larger the coil, the less relevant using litz will become. The advantages become mute. So using litz is not really appropriate for all coil sizes.

One other point I would like to mention, when it comes to litz, though standardized, you will not get manufacturers to sell the same configurations. This point alone will drive you insane because it will become difficult to find specific litz sizes. Most manufactures will sell only in bulk (1000+ feet), and don't like dealing with the little guy. This became an increasing source of frustration when I realized that the sellers who had my target litz sizes mostly dealt with corporate consumers. In fact, some of the litz wire Minelab uses is specially made for them. Like with White's and the others, you are not likely to find their litz wire very easily.

One last thing I would like to also mention, depending on the coil size, you're going to use different litz sizes. So, from coil to coil, Minelab will use different litz.

I don't want to discourage any body from using litz, because I'm sure any body can eventually work with litz. However, I think people should be aware of its issues.

[Rov]

Litz wires for coils PI?
nice if you like the expense an availability.?or you got a Chinese wires fabricator/manufacturer to make at$$$ in this age 2011?Not!
Go for the best Multistrand Tin plated copper for your $$,an dialectric pvc wires an you be fine.For your Minelabs GPX PI detectors,get the loom turns right,Coil casing and loom screening right for EMI to ground balance with fast timing setting etc.
as example try 19t multistrand medium duty tinplated copper over a 18x10 elliptical mono former to wind with good screening to the shells an loom to screen of coax to detector. will put you in the ball park for a low Ohms/inductance coil.this will work straight up an not hard! an no exotic materials other than Electrodag Paints.
Try it you will see?ballpark will be around 300uh/0.9ohms max.for this coil.
On Minelabs Gpx detectors,remember to autotune an let the detector scan for frequ.whilst elevated for a period till it sabilise.an check u ground balancing an u be fine as per your owners manual!Easy!
Yes I build these coils with satisfaction!
check my youtube for PMcoils on the net.
yes I detect a lot and I build a lot!
Cheers!Rov

[bklein]

From what I read about Litz wire here on the forum I'm thinking people are missing something about why it may be used. Which is why I posted the question of which one to get. Seems like people are thinking about their own tolerance to the weight of the coil without much wonder as to why they should use it. I'm thinking the key here is that such a coil is effectively multiple coils in parallel. Each strand is a coil. 100 strands and you have 100 coils in parallel. Why is that good? Well you would have a lower impedance signal. It would perhaps be faster response as a result. Lesser turns of the coil and you don't notice it. More turns and you would see the difference. So these discussions of whether or not it is worthwhile doing may be faulty in my view. There will always be a tradeoff between TX optimization and RX optimization if you are using the same coil for both. I wonder if we have been designing for TX more than RX....?

[mario]

Litz wires for coils PI?
nice if you like the expense an availability.?or you got a Chinese wires fabricator/manufacturer to make at$$$ in this age 2011?Not!
Go for the best Multistrand Tin plated copper for your $$,an dialectric pvc wires an you be fine.For your Minelabs GPX PI detectors,get the loom turns right,Coil casing and loom screening right for EMI to ground balance with fast timing setting etc.
as example try 19t multistrand medium duty tinplated copper over a 18x10 elliptical mono former to wind with good screening to the shells an loom to screen of coax to detector. will put you in the ball park for a low Ohms/inductance coil.this will work straight up an not hard! an no exotic materials other than Electrodag Paints.
Try it you will see?ballpark will be around 300uh/0.9ohms max.for this coil.
On Minelabs Gpx detectors,remember to autotune an let the detector scan for frequ.whilst elevated for a period till it sabilise.an check u ground balancing an u be fine as per your owners manual!Easy!
Yes I build these coils with satisfaction!
check my youtube for PMcoils on the net.
yes I detect a lot and I build a lot!
Cheers!Rov

Hi Rov,

Can you give me an example of this "19t multistrand medium duty tinplated copper" wire, I have tried doing a google search with no luck.

Thank you so much for your input,

Mario

[mario]

From what I read about Litz wire here on the forum I'm thinking people are missing something about why it may be used. Which is why I posted the question of which one to get. Seems like people are thinking about their own tolerance to the weight of the coil without much wonder as to why they should use it. I'm thinking the key here is that such a coil is effectively multiple coils in parallel. Each strand is a coil. 100 strands and you have 100 coils in parallel. Why is that good? Well you would have a lower impedance signal. It would perhaps be faster response as a result. Lesser turns of the coil and you don't notice it. More turns and you would see the difference. So these discussions of whether or not it is worthwhile doing may be faulty in my view. There will always be a tradeoff between TX optimization and RX optimization if you are using the same coil for both. I wonder if we have been designing for TX more than RX....?

Only one response: Good luck.

Please post your findings.

I have had moderate success with litz, but have not been completely satisfied with results. My advice, use thicker litz than expected, since you will find no inductance calculator using litz. Don't forget, as more strands "stray" at terminals (ALL strands have to be soldered, and this alone may be difficult since ALL strands are individually shielded), any advantage using litz will quickly begin to null.

Working with litz is not easy, and I will only recommend it to people who have made several coils prior before considering using litz.

[bklein]

Yeah, I called a manufacturer today and spoke with the owner for over an hour I think. He knew his stuff and works with an interesting customer group. He says if the wire kinks, and it tends to, its history. And if you touch it with your hands the grease on your fingers may degrade it over time... I ordered some 100 strand stuff on ebay to play with, let you know if anything looks good with it.

[Stefan]

I have been making coils successfully for many many years using litz wire. I had problems finding the right size litz from manufacturers so endeavoured to make my own. It is easy to make but time consuming to get right and not for the novice. Need to use the right type of enamel on the wire otherwise it becomes very difficult to solder and you may end up having broken strands or high resistance joints. The wire has to be twisted and if you don't get this right you will break strands.

Essentially the number of strands determines the Q of the coil. Break a strand and the Q goes down. Which means that the sensitivity of the coil goes down.

If you use x strands for say a 14 inch mono coil to give you the required Q then for a 18 inch coil you will need x + more strands for the same Q.

The raw litz wire will need an outer coating to minimize inter winding capacitance and provide a further insulation from adjacent litz in the coil. Normally a silk covering is used but I use another material.

You need to specifically tailor the litz wire bundle for each size coil.


Stefan

[Carl-NC]

I'm thinking the key here is that such a coil is effectively multiple coils in parallel. Each strand is a coil. 100 strands and you have 100 coils in parallel. Why is that good? Well you would have a lower impedance signal. It would perhaps be faster response as a result.

Barry,

100 strands = 100 coils in parallel, true, but each strand carries 1/100th of the current. Net result (from purely a DC perspective) is no net gain; same field generated.

Litz advantages only occur with AC in terms of minimizing self eddy losses and skin effect, and the higher the frequency the more so. I've always been skeptical that Litz provides any significant advantage in typical detector designs, even PI where we want very fast signals. If you build a Litz coil, you darned better have everything else peaked out as well, if you want to see the improvement.

If you're talking about making a balanced coil for PI, intuitively I expect that only the TX coil would make a difference. If the RX coil is reasonably balanced, then its speed matters less, and Litz would not buy you anything. Again, intuition, I have no empirical data.

- Carl

[Alexismex]

Hello Forum,
Do not be afraid from the name Litz , it is the same as easy to make a coil with it but you need more time to solder them because you need to peal every strands and solder good , here it is where i bought some years ago my litz wire:
http://www.surplussales.com/Wire-Cable/LitzWire.html
i use it only for small special DD coil ....
Alexis.

[WM6]

Hello Forum,
Do not be afraid from the name Litz , it is the same as easy to make a coil with it but you need more time to solder them because you need to peal every strands and solder good , here it is where i bought some years ago my litz wire:
http://www.surplussales.com/Wire-Cable/LitzWire.html
i use it only for small special DD coil ....
Alexis.

Hi Alexis

Here another possibilities to solder Litz wire without to peel out every strand.

You need to use some solder flux and very hot solder Iron (say 150 - 200W - no problem if more).

Put some solder flux at the end of litz wire. Heat solder iron and put on it enough solder. Put end of litz wire in very in those hot solder, wait second or two, and end of your litz wire are soldered without removing enamel. Now You can solder your litz wire where you need.

[bklein]

Barry,

100 strands = 100 coils in parallel, true, but each strand carries 1/100th of the current. Net result (from purely a DC perspective) is no net gain; same field generated.

- Carl

Yes, you are right- if you use small gauge wire the current output is low as its resistance per foot is higher. Is its signal output also lower because of it's diameter fundamentally or just due to the resistance aspect? One formula I saw for a rx antenna didn't mention wire diameter. I suspect you are right that to get the faster gold signal response we may be better off changing the coil configuration or separating rx and tx coils with an isolation scheme to then be able to work with the rx signal sooner. The signal is there it just has a 400v dc bias at the time...!