Coiltek Blitz coil

Anyone know about these coils
http://www.nuggethunting.com/forums/index.php?s=f45ba254f1ad01bcda34336e593a2b88&showtopic=8166

geof_junk wrote:Anyone know about these coils
http://www.nuggethunting.com/forums/index.php?s=f45ba254f1ad01bcda34336e593a2b88&showtopic=8166

i have not tried it, but i love the origanal 14x9, so if it's better than that, it's gotta be a good thing,
now all trevor needs to do is pot the wire in resien so they last longer
cheers

I don't know anything about these actual coils, but I do know about litz wire and it's properties. I'm struggling here to not spill my coffee (from laughing so hard) after reading that Minelab were actually able to get away with patenting the use of litz wire in metal detector coils.


Litz wire is composed of strands of mono-filament wires which are insulated along their lengths with an enamel coating. This bundle of insulated wire filaments are terminated at each end so that all the strands are electrically connected together. Litz wire is used to counteract a phenomenon called the "skin effect" which causes the current to travel closer to the surface of the conductor than through it as the frequency of the current increases. This results in higher impedance and power dissipation in the form of heat generation. Generally, litz wire is used in applications where the frequency exceeds 50khz and considering a Minelab GPX detector runs at approximately 8khz I cannot really see any benefit to using it. In my opinion it is preferable to reduce an inductors (detector coil) parasitic capacitance by using specialised insulating materials such as teflon which will increase its response time/sensitivity.


In think this is just a $500.00 gimmick with no discernible benefit whatsoever.

I guess we can talk about it now. And yes, Minelab had indeed patented the use of LITZ wire for the use in metal detector coils. You could certainly build your own coils with LITZ wire in the past if you wanted to ...although if you tried to sell it commercially, you'd probably have run afoul of the patent laws.

I don't think you could consider it a 'gimmick' though. Some people prefer the LITZ wire over other alternatives and Minelab knows why it can have an advantage over other types of wire on a coil. Coiltek appears to have made only a handful of these new coils to test the water with. One of the big selling for coils using LITZ wire in the past was the properties of the wire used. There are several types of LITZ so only specific types seem to be the suitable ones for applications in detecting.

There's definitely benefits in using LITZ over other types of wire (according the Minelab) although this hasn't prevented other detector manufacturers and coils manufacturers from producing successful products. The gap between the individual strands of wire has a dramatic effect on the performance and output but Coiltek has managed to produce many coils without LITZ wire which users often swear by. I certainly wouldn't consider it a 'gimmick' to use or even try... but perhaps someone with more understanding of the possible benefits can explain in detail. I've used a few Coiltek coils with the conventional wiring to know they're already decent coils. It's often a personal preference thing. I noticed a fairly distinct response on targets with the standard wire coils.

I think there have been a few short articles printed why some manufacturers use LITZ wire in detecting.

If the cost of manufacture was not an issue I would use litz wire over standard multi-strand wire for the minuscule benefit (reduced eddy currents) it offers in this application. I have here in my lab a GPX5000 with the standard 11" mono that has been wound with litz wire. I also have a test coil which I constructed from an 11" acrylic laser-cut former which was wound with AWG 18 multi-strand, silver plated, teflon insulated wire. When I sample and overlay the waveforms from both coils on my more than capable 4GS/sec scope there is no discernible difference whatsoever. AWG 18 wire can get full skin depth at 18khz which is more than adequate to construct a coil from to use with a GPX machine running at 8khz. Another thing to note here is that despite the GPX detectors being the staple out there and touted as being the best they really are not all that high-tech. They are far from being a precision instrument, and could have been built with readily available 80's technology. This brings me to the conclusion that it is pointless trying to eke out a minuscule amount of increased performance from the coil when most of the magic happens in the control-box. An analogy to this is those 65+ Y.O audiophiles that will swear they can tell the difference between normal copper speaker cable and the oxygen-free copper cable.

Gday

Whether there is a significant difference between the use of litz wire over standard wire, it seems is always going be the subject of debate, as I dont make coils and only use them I cant say for sure either way, but if coiltek are now making their coils with litz wire which I am led to believe is more costly than the standard wire that they have been using, then they must be doing it for one of two reasons.

Either the litz wire will and does increase the performance of coils and they know this, or its purely so that the quality and performance of the coils would be percieved by buyers as being the same as other brands currently on the market because they are using litz wire, either way it does not matter as many people have their own preferences as far as coils brands go, just as they do to the many shapes and sizes.

I have observed that most people will persist in using one coil for the majority of their detecting (this includes me) and this is usually how most people will end up with a favorite coil, and if you are finding gold with it on a regular basis it stands to reason, it does not really matter what brand it is as long as you are getting the gold with it.

cheers

stayyerAU

As far as I'm aware Minelab never did patent litz wire for application as a search coil wire for detectors. I heard they tried this but Whites detectors challanged the patent in the U.S. courts and stopped the patent going through. I could be wrong and a patent search may prove this one way or another. It would be interesting to know but I'm not interested enough to bother doing a search.

Cheers, Jim

I thought someone might be interested in seeing the patent for minelabs litz wire coils.Rwork

(WO/1987/003380) METAL DETECTOR SENSING HEAD WITH REDUCED EDDY CURRENT COILSBiblio. DataDescriptionClaimsNational PhaseNoticesDocumentsLatest bibliographic data on file with the International Bureau

Permanent LinkBookmark this page
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Pub. No.: WO/1987/003380 International Application No.: PCT/AU1986/000366
Publication Date: 04.06.1987 International Filing Date: 26.11.1986
IPC: G01V 3/10 (2006.01)
Applicants: MINELAB ELECTRONIC INDUSTRIES LTD. [AU/AU]; 18 Eliza Street, Adelaide, S.A. 5000 (AU) (All Except US).
CANDY, Bruce, Halcro [AU/AU]; (AU) (US Only).
Inventor: CANDY, Bruce, Halcro; (AU).
Agent: COLLISON & CO.; 117 King William Street, Adelaide, S.A. 5000 (AU) .
Priority Data: PH 3573 26.11.1985 AU

Title: METAL DETECTOR SENSING HEAD WITH REDUCED EDDY CURRENT COILS
Abstract: A sensing head for a metal detector including means for magnetic transmission and detection of a retransmitted signal from a target by means of at least one coil, the head being characterised in that at least some of the conductor material forming the coil and providing for passage of current through the coil is such as to provide for such passage wherein the arrangement is such or the selection of conductor material is such as to restrict the magnitude of eddy currents in the conducting material. Coils wound from wires in parallel, and in particular, Litz wires, are disclosed.
Designated States: AU, BB, BG, BR, DK, FI, HU, JP, KP, KR, LK, MC, MG, MW, NO, RO, SD, SU, US.
European Patent Office (EPO) (AT, BE, CH, DE, FR, GB, IT, LU, NL, SE).
Publication Language: English (EN)

Thanks for posting that patent Rwork. I am quite surprised that the patent was granted and it's for this reason that innovation is stifled by large companies that patent everything they can and eliminate their competition which in turn allows them to command exuberant prices.


Initially for fun I developed my own PI detector which performed surprisingly well. Encouraged by my results, I investigated the possibility of developing it further into becoming a marketable product but soon realised Minelab would run me through the courts in a flash. I am now considering starting an "open source" PI community and will kick it off with my designs thus far. I may start a new thread on this topic so I can gauge what the interest out there will be.

Thanks for that information, Bytman. I didn't think they actually had the litz wire patented and I agree that this is not a good thing for the industry. Their detectors are, and should be, under patent as they do own the intelectual rights to these but to patent a wire thats been around for 60 or 70 years for an application that many manufacturers had been using the wire for decades before is just plain wrong. However, there are plenty of wires out there that do just as good a job as Litz wire when used in search coils so maybe its not so bad.

Cheers, Jim

Doesn't the Advantage coils use litz wire as well as the Minelabs?
Paul

I have done countless testing on coils and found that there is zero performance gain in using Litz wire in a metal detector (P.I) coil. If anything it have actually increase interference to the detector from low and medium frequency radio transmitters. As long as Eddy currents die off before the receiver turns on then there is no problem.

Note the link about Blitz coils has been pulled off the other forum......I guess it is still not released yet.

woody wrote:If anything it have actually increase interference to the detector from low and medium frequency radio transmitters.

It might be just me but, i find the ADV models over 14" round tend to pick up more EMI in peak times then the older white models i still use. 16" round 17" elip & 14" round.

They run very smooth over commonly noisy ground then the older models, but i found them to be more susceptible to EMI. ?? could be just me tho. yet it fits in with the above quote.???

Im sure i read that the use of Litz wire in these models was more sensitive then that used in the older models?? could it be the shielding used.??

Interesting stuff whatever the case.??

woody wrote:I have done countless testing on coils and found that there is zero performance gain in using Litz wire in a metal detector (P.I) coil. If anything it have actually increase interference to the detector from low and medium frequency radio transmitters. As long as Eddy currents die off before the receiver turns on then there is no problem.

I agree with you except I cannot comment on external interference as I did my testing in a Faraday cage.

I attempted testing in a Faraday cage but found that while it blocked most electric field interference it had no effect on any magnetic flux cutting the coil windings and generating spurious noise.

The use of litz wire in MF inductors has beeen well investigated. The reduction of skin effect becomes noticable above 1KHz. The reduction of proximity effect is more dramatic and A litz inductor will have a much higher "Q" (efficiency) than a single wire inductor. In practice the use of litz wire at frequencies below 100KHZ over the use of teflon insulated siver is neglidgable. I do hypothosise that the use of litz wire in combination with teflon silver in DD coils can take advantage of the better characteristics of both. Below is some of the maths for use of litz.
Regards Eric (electronics engineer in previous life) now retired in S.A. with no affiliation to minelab

Squared-field-derivative method

This can be used for round wire or litz wire transformers or inductors with multiple windings of arbitrary geometry with arbitrary current waveforms in each winding. The diameter of each strand should be less than 2 δ. It also assumes the magnetic field is perpendicular to the axis of the wire, which is the case in most designs.

Find values of the B field due to each winding individually. This can be done using a simple magnetostatic FEA model where each winding is represented as a region of constant current density, ignoring individual turns and litz strands.
Produce a matrix, D, from these fields. D is a function of the geometry and is independent of the current waveforms.

\mathbf{D}=\gamma_1 \left \langle \begin{bmatrix} \left | \hat{\vec B_1} \right |^2 & \hat{\vec B_1} \cdot \hat{\vec B_2} \\ \hat{\vec B_2} \cdot \hat{\vec B_1} & \left | \hat{\vec B_2} \right |^2 \end{bmatrix} \right \rangle_1 + \gamma_2 \left \langle \begin{bmatrix} \left | \hat{\vec B_1} \right |^2 & \hat{\vec B_1} \cdot \hat{\vec B_2} \\ \hat{\vec B_2} \cdot \hat{\vec B_1} & \left | \hat{\vec B_2} \right |^2 \end{bmatrix} \right \rangle_2

\hat{\vec B_j} is the field due to a unit current in winding j
<.>j is the spatial average over the region of winding j
\gamma_j = \frac{\pi N_j l_{t,j}d_{c,j}^4}{64 \rho_c}

N_j is the number of turns in winding j, for litz wire this is the product of the number of turns and the strands per turn.
l_{t,j} is the average length of a turn
d_{c,j} is the wire or strand diameter
\rho_c is the resistivity of the wire

AC power loss in all windings can be found using D, and expressions for the instantaneous current in each winding:

P = \overline{\begin{bmatrix} \frac{di_1}{dt} \frac{di_2}{dt} \end{bmatrix} \mathbf{D} \begin{bmatrix} \frac{di_1}{dt} \\ \frac{di_2}{dt} \end{bmatrix}}

Total winding power loss is then found by combing this value with the DC loss, I_{rms}^2 \times R_{DC}

The method can be generalized to multiple windings.

I'm building a large Pulse Induction coil for minelab GPX detector.

I opened up an 11" (~28cm) coil and the wire is 36 strand. 0.4 Ohms, 0.28 mH.
My new larger coil tested as 0.4 Ohms, 0.08 mH, I need to increase the Inductance (mH) of this to match the original.

I found out that an 18" (~46cm) uses 72 strand wire, my coil is larger (1 metre diametre).
As they've doubled the amount of strands, for a ~64% increase in diametre.
I calculate that I'm making a ~117% increase in diametre over the 18" coil.
I've not been able to measure the Inductance of the 18" but I expect it to be similar.
Just curious if you can tell me if I can do some maths to work out how many strands I'll need in my Litz wire to bring it up to 0.28 mH?

Here is the page stating the range of Litz wire they have available:
elektrisola served litz wire (as a new member I'm not allowed to post a link.)

I wonder if the Dielectric constant(relative permittivity) is a factor?

Thanks so much
Nathan

GoldPandemic wrote:I'm building a large Pulse Induction coil for minelab GPX detector.

I opened up an 11" (~28cm) coil and the wire is 36 strand. 0.4 Ohms, 0.28 mH.
My new larger coil tested as 0.4 Ohms, 0.08 mH, I need to increase the Inductance (mH) of this to match the original.

I found out that an 18" (~46cm) uses 72 strand wire, my coil is larger (1 metre diametre).
As they've doubled the amount of strands, for a ~64% increase in diametre.
I calculate that I'm making a ~117% increase in diametre over the 18" coil.
I've not been able to measure the Inductance of the 18" but I expect it to be similar.
Just curious if you can tell me if I can do some maths to work out how many strands I'll need in my Litz wire to bring it up to 0.28 mH?

Here is the page stating the range of Litz wire they have available:
elektrisola served litz wire (as a new member I'm not allowed to post a link.)

I wonder if the Dielectric constant(relative permittivity) is a factor?

Thanks so much
Nathan

Hi Nathan.

You need to locate someone with a meter that reads inductance etc. They will then be able to help you with getting the answers you want.
There are coil calculators you can google on the net, each with a formula depending on which type of coil you have decided to construct.

These calculate the number of turns needed, the wire gauge, also the length required and the spacings to allow between the winds etc.
With mono coils you have to aim for is an inductance of 300 Uh. Especially when using it on a Minelab detector.

The size of the coil doesn’t matter here, as long as it meets that specific figure of near 300Uh.
However there are other measurements you have to consider. Like Resistance, Coil Q, capacitance etc.

With commercial coils, there are small and measurable differences in coil inductances, their capacitance and Q, particularly so with the larger coils.  E.G. GPX detectors do not like coils with a Q around the 3.8 / 3.9) this will affect the performance of the detector.

Good luck. Cheers, ozgold.

I can measure the Inductance, Resistance, Capacitance. Figuring out how many threads in my Litz wire is my task now.
I have tried the calculators but did not work out how to use them correctly.

Thanks for the info, I hope it helps me get some more answers.

GoldPandemic wrote:I can measure the Inductance, Resistance, Capacitance. Figuring out how many threads in my Litz wire is my task now.
I have tried the calculators but did not work out how to use them correctly.

Thanks for the info, I hope it helps me get some more answers.

Hi Nathan.

Safe to say if you are doing a flat wound coil, use 40 strand Litz, and you will have a winner.
This whole thing may change depending on what type of coil you want to wind??

Cheers ozgold.

I reckon I need 144 strand litz wire.

Sorry, didn't want to hijack this thread (just unable to send Private Messages as a new user).

GoldPandemic wrote:I reckon I need 144 strand litz wire.

Sorry, didn't want to hijack this thread (just unable to send Private Messages as a new user).

Have you had a look at the Geotech calculator?
http://www.geotech1.com/forums/showthread.php?17909-Coil-Calculator