DIY Mad Litz Wire for ULTRA FAST PI Coils

[Qiaozhi]

One other thing I have found is that winding a neat tidy layered coil does NOT help depth (or seem to). Some of the best coils I have made were ones I scramble wound to test a front end. Bizarre or what?

Neatly layering the windings will result in maximum inter-winding capacitance (i.e. a slower coil).

[Sean_Goddard]

One other thing I have found is that winding a neat tidy layered coil does NOT help depth (or seem to). Some of the best coils I have made were ones I scramble wound to test a front end. Bizarre or what?

[6666]

I think it's because the larger wire is acting as a target longer

That makes sense, thanks.

[green]

Thats a good graph, but I'm not sure I understand the results properly, when I saw the graph a while back, I was looking at the SRF number and 24 awg PVC wire had the highest SRF, meaning to me, that it had the lowest capacitance (maybe not ?) but it comes out of saturation last of the three, I'm confused .

I think it's because the larger wire is acting as a target longer. http://www.geotech1.com/forums/showt...725#post213725 Litz_2 chart includes a chart of wire TC for awg12, awg19 and awg24 that I recorded. Maybe not the reason but it's my best guess. The awg24 had the highest SRF, mayby because of the lowest inductance.

The SRF of the coils are probably higher than charted. They were measured in circuit with the damping resistor removed. I now excite the test coil with another PI and measure the resonance with the operating PI which gives a higher SRF

[6666]

One last thought, why not put the Tx drive FET and Rx Preamp IN the search head

MikeBG published a circuit to do that, been looking for it, will keep trying to find it.

[6666]

The coil comes out of saturation sooner with the smaller strands. litz, then awg28, then awg24.

Thats a good graph, but I'm not sure I understand the results properly, when I saw the graph a while back, I was looking at the SRF number and 24 awg PVC wire had the highest SRF, meaning to me, that it had the lowest capacitance (maybe not ?) but it comes out of saturation last of the three, I'm confused .

[green]

Well I think BBSailor explained it better than I did. TY also to 6666 ;-).

I have tried the monofilament idea (was mine in the first place) to wind a spiral coil using copper wire then 100lbs monofilament along side it. Better still, use the Rx coil and wind the two side by side for fantastic coupling. Even BETTER is to overwind (more turns in the Rx than the Tx) the Rx for a transformer type action.

Better than nylon, use FLOUROCARBON, it has a much better dielectric coefficient than monofilament. Try the FlouroCarbon with the above multi core wound in a spiral or basket weave and see how that works.

Can someone post some oscilloscope shots on here when they do comparisons please? I'd do the work but I am too short of time atm and can only suggest things to try. Sorry.

One last thought, why not put the Tx drive FET and Rx Preamp IN the search head? No coax capacitance to discharge then and you could use a current loop system to drive the signal to the control box.

ENJOY!

http://www.geotech1.com/forums/showthread.php?22895-Litz-wire-size-for-coils&p=213770#post213770

Some coil comparisons I did awhile back with awg28, awg24 and some litz wire. Not sure it's the best test to compare coils. Amplitude was close for all the coils. The larger diameter wire was a little lower amplitude, lower inductance. Adjust turns to get same inductance should get amplitude closer. The coil comes out of saturation sooner with the smaller strands. litz, then awg28, then awg24. Need to define a good test procedure to see the differences when winding the coils.

[Sean_Goddard]

Well I think BBSailor explained it better than I did. TY also to 6666 ;-).

I have tried the monofilament idea (was mine in the first place) to wind a spiral coil using copper wire then 100lbs monofilament along side it. Better still, use the Rx coil and wind the two side by side for fantastic coupling. Even BETTER is to overwind (more turns in the Rx than the Tx) the Rx for a transformer type action.

Better than nylon, use FLOUROCARBON, it has a much better dielectric coefficient than monofilament. Try the FlouroCarbon with the above multi core wound in a spiral or basket weave and see how that works.

Can someone post some oscilloscope shots on here when they do comparisons please? I'd do the work but I am too short of time atm and can only suggest things to try. Sorry.

One last thought, why not put the Tx drive FET and Rx Preamp IN the search head? No coax capacitance to discharge then and you could use a current loop system to drive the signal to the control box.

ENJOY!

[bbsailor]

The twist of the wires is called "wire lay". If you look into the end of the wire and see the slant of the twist that matches the slope of the center of letter Z, it is called a "Z-lay". If it matches the slop of the letter S,(wound in the opposite direction) it is a "S-lay".

The purpose of winding the parallel strands in this way is to try to minimize the inductive component in the wire. Straight wire has about a 0.4 micro-Henry inductive component per foot. So, winding strands and wire bundles in opposite ways is one technique to try to minimize parasitic inductive component of the wire. Then, increasing the spacing between winds is a way to try to minimize the parasitic capacitance coupling between coil turns.

All electronics components follow electronic theory as pure representatives of their component type and value. However, in the real world, real electronic components have parasitic values of other components that change at various power levels, frequency and speed.

Here is a common example that applies to Pulse Induction Metal detectors. The value of the damping resistor is an attempt to quench the energy in the flyback pulse as fast as possible to quickly change the coil from the transmit mode to the receive mode. Why? After the TX pulse turns off the TX energy, that quick change induces energy (eddy currents) into nearby metal objects. While the PI circuit is in the delay time, the energy in the target is starting to fall. As soon as the RX circuit is activated, the decaying eddy currents in the target are now capable of being detected. In small targets such as gold, the currents decay so fast that there is little left when the RX mode is activated. That is why low delay is desirable for these low Time Constant type targets.

When you have parasitic capacitance in a coil, the damping resistor does not immediately suppress the flyback pulse because the parasitic capacitance of the coil, coax cable and MOSFET collectively cause the flyback pulse energy to oscillate and take more time to be damped to very near zero when the RX circuit can be activated.

How you get the delay time lower can be done in a few ways. Lower TX circuit capacitance or lower the power in the TX pulse to have less energy to damp. This is why gold detectors operate at a higher frequency with shorter TX pulse widths and typically have higher values of damping resistors. If the delay time is able to be very low but there is still eddy currents decaying in the coil wire itself, then the physics of the coil wire is preventing any further delay reduction. Using Litz wire is a way to have many parallel strands carry enough current to stimulate a target but have thin enough strands that eddy currents in the wire itself does not restrict the very early delay transition to the RX mode.

The winding techniques of using S-lay and Z-lay bundled wire is another technique to attempt to minimize the parasitic inductive components of the wire itself in an attempt to better stimulate a target and then quickly detect that target.

It would be interesting to see actual use of this wiring technique in some gotech1 forum member experiments with shared results.

This is just my best analysis as to the value of using this type of wire. I hope Sean jumps in to comment on my analysis share his results.

Joseph J. Rogowski

[Jose]

Thanks for the link, bbsailor.
Thanks for the clarification, 6666.
Jose

[Skippy]

I wonder how much of this observed 'speed' change is due to the wires no longer running absolutely parallel, and how much is due to the wires being further apart, and there being less coupling and interaction between strands?

Interesting experiment idea: in the first step, twist 2 copper strands and one strand of monofilament nylon together. Then proceed as before.

[6666]

Hi Sean Goddard
Thank you for sharing this interesting topic.
Unfortunately some concepts I can not understand, partly by the translation and by my ignorance of the subject.
Would appreciate if someone does a graphic scheme, or publish an image to understand better.
Thanks again, best regards
Jose

Basicly he is saying instead of twisting a big bunch of parallel wires in the one direction ,
Groups of wires are twisted together in opposite directions

start by twisting two pairs of wires in opposite directions, < >

then twist those two pairs together (2+2) = 4 in one direction
then twist another two pairs together (2+2) = 4 in opposite direction

So then you have 4 + 4 =8, etc.

[homefire]

A Square wave in made up of a Infinite number of Harmonics of the Base Wave. How would that effect Damping ? Thin could be good on
damping times?

[bbsailor]

To everyone tinkering with coils,

Here is a link that will give you more information about Litz wire. http://litzwire.com/nepdfs/Litz_Design_PDFs.pdf
The most important thing to consider is the actual strand size as the strand sizes are frequency dependent. An AWG 30 strand would be good to use from 1KHz to 10KHz. As the frequency goes up the strand size gets smaller.

I hope this helps.

Joseph J. Rogowski

[Jose]

Hi Sean Goddard
Thank you for sharing this interesting topic.
Unfortunately some concepts I can not understand, partly by the translation and by my ignorance of the subject.
Would appreciate if someone does a graphic scheme, or publish an image to understand better.
Thanks again, best regards
Jose