DIY Mad Litz Wire for ULTRA FAST PI Coils

[6666]

I think this may reduce the effectiveness of the coil. It will reduce it's depth. At least this was my experience with enamel copper wire, not sure about mult strand.

I was talking about speaker wire, not solid enamel copper wire,

[bbsailor]

To stay within the scope of the title of this thread, please keep in mind that the ability of a current that rises to its maximum and is quickly cut off, creates a discharge time constant. The more vertical this discharge current is depends on the value of the damping resistor (Rd). Higher Rd values means less capacitance to suppress as well as potentially faster times to turn on the RX portion of the circuit (delay time). With extremely small targets that are desired to be detected, it becomes extremely important to fully stimulate the target with the fastest discharge current to fully stimulate most eddy currents in the target. Here is where Litz wire comes into play.

Look at this web link: http://litzwire.com/litz_types.htm. Look at type 2 as it contains bundles of strands wound in opposite directions. This type will minimize the straight wire inductance, typically 0.4 Micro Henries per foot, and create a better opportunity for the current discharge to be more vertical, with less of a rounded edge on an oscilloscope pattern display. Quicker discharge Time Constants (TC) stimulate smaller targets better. You need to choose Litz wire with very small strands in the bundles to easily represent the harmonics many time higher than the PPS rate of your pulse induction metal detector. The rule of thumb is to make the coil discharge TC 5 times smaller than the TC of the target you are seeking.

Here is where total coil circuit capacitance, damping resistor value and coil wire eddy current retention minimization come into play to optimize your coil for what you are seeking.

Joseph J. Rogowski

[green]

Mostly just trying to learn or understand why. If I record the decay with 2 stacked US nickels. Touching or with a layer of masking tape between them they chart the same decay, about twice the TC of a single coin. Was thinking stranded wire might not be effected by conductance between wires, looks like I was wrong. Maybe someone could explain why. Posted a test with coils made using different wire in another thread awhile back. http://www.geotech1.com/forums/showt...103#post214103. Litz wire was a little better than solid awg28. Tx current was controlled to be the same for all the coils.http://www.geotech1.com/forums/attac...8&d=1456683394, attachment from other post.


Started reading the thread from the beginning again. Looks like some of this is a repeat. Has anyone tried winding a coil as suggested to see if it is faster. I don't see a big difference between litz and solid awg28, maybe something I'm doing wrong. Would be interested where someone has compared different coils and seen a big difference.

[IBGold]

Hi Bernte-one,

No performance details yet it is still at picture stage and will be for another 4 weeks at least as I am recovering from a full shoulder repair will give you a report when completed.

Regards, Ian.

[bbsailor]

Mostly just trying to learn or understand why. If I record the decay with 2 stacked US nickels. Touching or with a layer of masking tape between them they chart the same decay, about twice the TC of a single coin. Was thinking stranded wire might not be effected by conductance between wires, looks like I was wrong. Maybe someone could explain why. Posted a test with coils made using different wire in another thread awhile back. http://www.geotech1.com/forums/showt...103#post214103. Litz wire was a little better than solid awg28. Tx current was controlled to be the same for all the coils.http://www.geotech1.com/forums/attac...8&d=1456683394, attachment from other post.


Started reading the thread from the beginning again. Looks like some of this is a repeat. Has anyone tried winding a coil as suggested to see if it is faster. I don't see a big difference between litz and solid awg28, maybe something I'm doing wrong. Would be interested where someone has compared different coils and seen a big difference.

Green,

Loosely stack coins may not have enough metal contact between coins to make much of a difference than single coins or coins insulated from each other by tape. They may be peformaning more like laminations in a transformer core to minimize eddy currents by having many thin layers electrically isolated from each other by their coating or not having much area of each coin layer conductive to the other coin due to the raised images.

Try this experiment. Obtain two nylon screws and bolts and a piece of nonconducting plastic, drill two holes in the plastic and make sandwich-like vice to squeeze the coins together. Since coins have a raised surface, even if squeezed together there may not be too much contact between coins. The real test is: viewing any output differences between individual coins, loosely stack coins and clamped coins for any differences caused by longer eddy currents being retained in thicker conductive materials.

This can also be done by obtaining some scrap metal samples cut to the same approximate coin size/area but using different metal thicknesses. Usually it takes a longer TX pulse to get down deeper in the core of thicker metals beyond the typical surface only charge. This is why metal detectors used to hunt for large underwater metal targets such as: cannons, cannon balls and boat wreck large metal parts use pulse lengths measures in milliseconds to more fully stimulate their desired targets.

I hope this helps?

Joseph J. Rogowski

[green]

However, multiple thin strands that are silver plated may act more like a thicker solid strand relative to eddy current retention due to the highly conductive silver plating on the strands from reply #54 bbsailor


Finally understanding what may means. Another test with awg16 wire(solid and stranded"26strands of awg30" cut from 110v power cord). Stranded shows no signal until I wrapped it tightly with thread to compress the wires together or soldered the end. Bent solid wire with a piece of paper between, charts about the same as straight piece. TC increased with bent wire wrapped with thread when laying flat, not much on edge. Need to get some silver coated stranded wire to test.

Chart should be .4v/decade
stranded wire not coated, think solid is tinned buss wire

[green]

@green
The size of the wires being used in your tests are so large, that I think that the other characteristics of litz wire that result in high srf and fast eddy current decay are being masked. Try using #20-24 litz wire made up of 300-400 strands of #36-40 wire. I suspect that you will see a difference.

As an aside, for those wondering how on earth can you solder the stuff, think "caustic paste paint remover". Dip the end in the paint remover, wait a few minutes and gently wipe with a cotton swab on a hard surface until the enamel is gone. If not, dip again, rinse and repeat. Some types of enamel are tougher than others, but eventually they all fail. Dip in rosin flux before soldering. Some litz wire may use enamel that melts at soldering temps.

Some data with smaller wire. Tried awg28 7x36 Teflon coated(the only Teflon coated wire I have). No indication, stripped and soldered still no indication with my tester(projected .3usec TC). I see Teflon coated wire being recommended for coils. Most is silver platted, did find some nickel platted. Does silver platted always act like solid? Charted some awg24 wire. No indication with litz and stranded until I stripped the insulation from one end and tinned the wires with solder. The soldered wire is the same as solid. Not a large signal with my tester so I added a .8usec TC line(projected TC from copper wire chart). Decay looks close to .8usec. The litz is slightly larger than awg24 and charts a little higher TC. Couldn't use log out because log out had to much delay with such a low signal. The litz I have does melt at solder temperature, easy to use. My tester isn't the best for looking at such short TC targets. Would be interested what a high frequency VLF(gold)detector would show.

[rickb]

How are you performing the test? Test equipment for any electrical parameter must be at least 5 (preferably 10) times better that what is being tested or measured.

[bbsailor]

Some data with smaller wire. Tried awg28 7x36 Teflon coated(the only Teflon coated wire I have). No indication, stripped and soldered still no indication with my tester(projected .3usec TC). I see Teflon coated wire being recommended for coils. Most is silver platted, did find some nickel platted. Does silver platted always act like solid? Charted some awg24 wire. No indication with litz and stranded until I stripped the insulation from one end and tinned the wires with solder. The soldered wire is the same as solid. Not a large signal with my tester so I added a .8usec TC line(projected TC from copper wire chart). Decay looks close to .8usec. The litz is slightly larger than awg24 and charts a little higher TC. Couldn't use log out because log out had to much delay with such a low signal. The litz I have does melt at solder temperature, easy to use. My tester isn't the best for looking at such short TC targets. Would be interested what a high frequency VLF(gold)detector would show.

Green,

Another thing to consider is the ability to move the coil connection point to the coax feed wire outside the coil housing where if it were inside the housing, it may act as a target at very low delays. Try extending the Litz coil wires about 6 inches above the coil and make the connection to the coax outside the coil housing or run the Litz wire up to the control box. You will need to find a way to eliminate or minimize noise pickup by some creative way to shield the extended coil wire without the shield being detected.

Litz wire is very good with high PPS rate TX pulses. Note which wire types give you the sharpest edge on the turn off current pulse. I have used very thin silver coated strands in Teflon insulated AWG 28 down to about 7 uS delay. Reducing coil and TX circuit capacitance allows the use a higher value of damping resistors which produces a coil discharge TC more vertical and better able to fully stimulate smaller, lower TC targets.

Thinner wire strand diameters have less coil turn-to-turn capacitance than thicker stranded wire diameters. Teflon wire usually comes in 300V rating and a 600V rating with a thicker layer of insulation which produces less coil capacitance. You may need to add a coil turn or two to make your desired coil inductance as coil wires more spread out have less inductance.

Joseph J. Rogowski

[green]

How are you performing the test? Test equipment for any electrical parameter must be at least 5 (preferably 10) times better that what is being tested or measured.

Using the tester I put together.http://www.geotech1.com/forums/showt...255#post239255 post #1 describes tester. I have two coils. Rx(2 round 1.5inch coils connected in a figure eight, Tx(oval surrounding Rx) and Rx(2 round 8inch coils connected in a figure eight, Tx(oval surrounding Rx). Used the smaller coil for testing the wires. Record log amp out with DSO when log amp is fast enough. Record amplifier out, target recording and no target recording and chart with Excel when log amp isn't fast enough. Log out was fast enough for the larger wires, not for awg24. I've been wanting someone to post tests to compare if mine makes sense. TC vs AWG would be nice. Reply#58 gives a method to increase the resistance between strands of wire. I haven't found it necessary with the non platted stranded wire I've tested. If I wrap the stranded wire with thread to compress the wires together for better conduction the stranded wire acts as solid so I see where it might be needed. Detecting the wire takes less signal than trying to chart the decay TC so when I say no indication it might still be detectable after post processing. Still haven't got the answer if silver plated stranded is the same as solid or it may be same as solid. Soldering it makes it same as solid. Has anyone tried making the ultra fast litz wire coil to see how much faster it is?

[green]

Green,

Another thing to consider is the ability to move the coil connection point to the coax feed wire outside the coil housing where if it were inside the housing, it may act as a target at very low delays. Try extending the Litz coil wires about 6 inches above the coil and make the connection to the coax outside the coil housing or run the Litz wire up to the control box. You will need to find a way to eliminate or minimize noise pickup by some creative way to shield the extended coil wire without the shield being detected.

Litz wire is very good with high PPS rate TX pulses. Note which wire types give you the sharpest edge on the turn off current pulse. I have used very thin silver coated strands in Teflon insulated AWG 28 down to about 7 uS delay. Reducing coil and TX circuit capacitance allows the use a higher value of damping resistors which produces a coil discharge TC more vertical and better able to fully stimulate smaller, lower TC targets.

Thinner wire strand diameters have less coil turn-to-turn capacitance than thicker stranded wire diameters. Teflon wire usually comes in 300V rating and a 600V rating with a thicker layer of insulation which produces less coil capacitance. You may need to add a coil turn or two to make your desired coil inductance as coil wires more spread out have less inductance.

Joseph J. Rogowski

You can starts with any number of strands you want but you are aimng for the FINAL CSAe (cross secional area EQUIVALENT) or 16AWG, thus you will need to work out how may "pairs" you need to twist up to get to the final COPPER CSA (not bundle as that includes the enamel) From post#1


Don't know why AWG16 and ultra fast coil go together. AWG16 would be for high current, high current takes longer to decay(time at avalanche volts). 16AWG has a TC of 5usec so the solder joint could probably be seen above very low delays. I've been using twisted pair instead of coax for feed line. Seems to work, less capacitance not sure it's best way.

[green]

What is best way to join 2wires for minimum target signal? Tried some different connections with awg19 and 22 solid wire. Including a chart and picture of the best I found. Similar results with awg19 and 22. Charted awg19, more signal strength. Soldered joint was near coil center, V(soldered joint vertical) H(soldered joint horizontal). Is there a better connection to try?

[bbsailor]

What is best way to join 2wires for minimum target signal? Tried some different connections with awg19 and 22 solid wire. Including a chart and picture of the best I found. Similar results with awg19 and 22. Charted awg19, more signal strength. Soldered joint was near coil center, V(soldered joint vertical) H(soldered joint horizontal). Is there a better connection to try?

Different coil types will have a null zone somewhere within the coil area. Try to locate that null zone where the response is least intensive, and locate the joint there. This may be more available on DD type and D O D type coils where null zones may be more detectable than on mono coils.

Joseph J. Rogowski

[6666]

What is best way to join 2wires for minimum target signal? Tried some different connections with awg19 and 22 solid wire. Including a chart and picture of the best I found. Similar results with awg19 and 22. Charted awg19, more signal strength. Soldered joint was near coil center, V(soldered joint vertical) H(soldered joint horizontal). Is there a better connection to try?

Thats a great experiment Green, according to the minelab patent putting a ferrite bead over a soldered joint makes the joint less detectable, it would be very interesting to try on both a T and a - joint, its something I have wanted to try but have no way to test it do you have any beads ?

I think you have some 24AWG PVC covered multi strand wire I would be VERY interested if you could test a T and - joint with a bead thanks

There is some techno bable in this patent but not the one I want, its somewhere on my PC
https://patents.google.com/patent/US20110234214

[green]

Thats a great experiment Green, according to the minelab patent putting a ferrite bead over a soldered joint makes the joint less detectable, it would be very interesting to try on both a T and a - joint, its something I have wanted to try but have no way to test it do you have any beads ?

I think you have some 24AWG PVC covered multi strand wire I would be VERY interested if you could test a T and - joint with a bead thanks

There is some techno bable in this patent but not the one I want, its somewhere on my PC
https://patents.google.com/patent/US20110234214

Used awg18 to get more signal. No signal with just wire(no solder joint). Soldered joint TC a little higher than awg18 solid. Tried awg24, similar results with lower signal. Ferrite bead does hide the joint. A smaller ID bead would look better, what I had. Bead offsets coil IB. A shorter inline solder joint has less signal with about the same TC. Scope pictures 1v/div to keep from over scaling, ferrite bead saturated amplifier with Tx on.