Coil wire material experiments

[nonkapo]

Good evening to all,

When waiting for the board and parts for my Surf PI and reading posts on the forum following idea come to my mind. When i was younger i was very much in the HAM radio. It was very common especially on the higher bands to use copper wire covered by silver for winding the induction coils. I know it may become expensive if using such wire for the MD coil but just curious if there are any benefits? Another question was the winding of the coil, but with flat wire rather than round(as used in some welding machines). My questions are not based on much knowledge, and may be baseless abut i'm still curious if someone make any experiments in this direction and what kind of result was achieved.
Thanks.

[waltr]

Seems lots of pros and cons and even more discussion debate on this.

Best for you to just read almost all the threads here in the coil sub-forum so the debates, etc don't start up again.

[nonkapo]

Hmz good advise. At that time i have access to some retired military grade tube radios from which i can source such wires. However we are talking about short lenght when for a MD coil one will need much longer.

[bbsailor]

Good evening to all,

When waiting for the board and parts for my Surf PI and reading posts on the forum following idea come to my mind. When i was younger i was very much in the HAM radio. It was very common especially on the higher bands to use copper wire covered by silver for winding the induction coils. I know it may become expensive if using such wire for the MD coil but just curious if there are any benefits? Another question was the winding of the coil, but with flat wire rather than round(as used in some welding machines). My questions are not based on much knowledge, and may be baseless abut i'm still curious if someone make any experiments in this direction and what kind of result was achieved.
Thanks.

The type of wire, solid, stranded, Litz, silver coated strands, or whatever type can hold the eddy currents just like the target you are seeking to detect. At low delays you want to use stranded but not silver coated strands, to not hold eddy currents any longer than the delay setting of your pulse induction detector. The rule of thumb is to use strands no larger than than about AWG 30 to minimize retaining to much eddy currents in the coil wire itself. At very low delays, typically between 5 and 10 micro seconds you want to use Litz wire or fine stranded marine type wire to minimize eddy currents being retained in the coil wire.

I hope this helps.

Joseph J . Rogowski

[alex61]

Hi all. While making coils for a minelab ,I found the coax I was using could be detected by the detector how much of a problem could this be .thanks

[baum7154]

The major problem with coax feed lines is the amount of capacitance it contributes to the feed/coil system. Capacitance is the enemy of coil speed that is required to see small fast targets like small gold at short sample delays.

Regards,

Dan

[bbsailor]

The type of wire, solid, stranded, Litz, silver coated strands, or whatever type can hold the eddy currents just like the target you are seeking to detect. At low delays you want to use stranded but not silver coated strands, to not hold eddy currents any longer than the delay setting of your pulse induction detector. The rule of thumb is to use strands no larger than than about AWG 30 to minimize retaining to much eddy currents in the coil wire itself. At very low delays, typically between 5 and 10 micro seconds you want to use Litz wire or fine stranded marine type wire to minimize eddy currents being retained in the coil wire.

I hope this helps.


Joseph J . Rogowski

Here is some added information for coil builders.

Determine the coil wire gauge needed to obtain the desired/required coil DC resistance which determines the maximum coil current of the TX pulse. Typically this wire will be stranded between AWG16 up to AWG28. Try to use fine strands that are tin-plated rather than silver plated to minimize the potential for eddy currents to be held in the coil wire itself. Low resistance, silver coated strands make retaining eddy currents by the wire easier than having a slight resistance of tin-plated strands which potentially hold less eddy currents.

Wire insulation type and thickness.

Wire insulation thickness for 300V rated wire is thinner than for 600V rated wire. Thicker insulation holds the coil wire a little farther apart and minimizes coil turn-to-turn capacitance compared to using wire with the same type of insulation.
Insulation type is related to the dielectric constant of the insulation material. PVC insulation dielectric constants ranges between 4 to 6 and Teflon is about 2. Lower is better and it makes a coil with a higher self resonant frequency (when measured) and will produce a coil that can operate at lower delays for small target seeking.

As a thought experiment consider this. If you had a PI metal detector that could operate at 5 microseconds (very fast) delay, use it to test various samples of wire you plan to use on your coil. Choose the wire stranding type that is least detected. Litz wire has independently insulated strands but requires you to clean each strand to ensure that all the strands are connected to the coil feed coax wire or reach up to control case and attach to the PI circuit board as an extension of the coil. At very low delays the solder joint between the coil and the coax feed line may act as a small target if located inside the coil housing.

I hope these additional tips get you moving in the right direction. I'm sure that other Geotech members can comment on their own coil building experience.

Joseph J. Rogowski

[alex61]

Thanks for your reply Dan and Joseph,very interesting.I have another Question With coil building we strive for the highest resonate frequency but I discovered that the 12 inch evo coil that has had very good reviews has only 510khz resonate frequency. Could this be because of the flat wind type on highly mineralised ground thanks again .

[nonkapo]

Very helpfull posts thanks a lot. So to sumarize, it sounds like if you are using Litz it is better to not use coax(which anyway brings capacitance) but use Litz it self as a feeder line? However what is the disadvantage of not shielded feedwire we have in such case? I expect it to get some noise/interference right?

[waltr]

Very helpfull posts thanks a lot. So to sumarize, it sounds like if you are using Litz it is better to not use coax(which anyway brings capacitance) but use Litz it self as a feeder line? However what is the disadvantage of not shielded feedwire we have in such case? I expect it to get some noise/interference right?

There is a thread here "shielded or unshielded" with answers/discussion.

As I stated above read the threads in this Coils sub-forum----All this has been discussed.

[nonkapo]

There is a thread here "shielded or unshielded" with answers/discussion.

As I stated above read the threads in this Coils sub-forum----All this has been discussed.

Sorry Waltr i read what you say, however result was 4 pages but i did not find such thread. Now after you mention again i do a bit more detailed search and i've got what you refer to so here the link if the questions still come.
http://www.geotech1.com/forums/showt...ded+unshielded