Stranded wire vs solid wire

[jladre]

Hello! It's been many times or a hundred of times that people taking about to this forum that stranded wire has less resistance compare to solid wire.. In my case i dont understand it because i already bought 4 kinds of wire in different brand but it seems that in 18 awg solid wire i get .7 ohm resistance for a 35 meter, but the 18awg stranded wire has 5 to 6 ohm resistance.. That why i ask anyone to give me answer why?..

[Davor]

It is not resistance that matters, but the largest cross-section. Multistrand has total area the same, hence the same resistance, but far less eddy current in wires.

[jladre]

It is not resistance that matters, but the largest cross-section. Multistrand has total area the same, hence the same resistance, but far less eddy current in wires.

Thanks davor!

[bbsailor]

It is not resistance that matters, but the largest cross-section. Multistrand has total area the same, hence the same resistance, but far less eddy current in wires.

There are two additional electronic points to this issue.
1. Skin Effect: where the current at higher frequencies travels on the surface of the wire. Since square waves, typical of pulse induction TX pulses, contain a very high frequency component, using a bundle of individually insulated wires (Litz Wire) the AC resistance is lower than the same size solid wire and carries a higher pulse current.
2. Residual eddy currents being detected in thick solid coil wire as a target. This becomes more of a problem as the target delay times are reduced near or below about 10 uS delay.

By using Litz wire each individual strand shares the same current and is thin enough to not have loss of AC current due to the skin effect. Also, because the bundle is made up of individual insulated strands the amount of eddy currents capable of being induced into the coil wire is very low and thus will not be detected.

If using tin plated stranded wire, there is a small resistance between the strands and this reduces the potential eddy currents that would be induced into the coil wire if it were solid wire or have a lower resistance like using silver plated multi-strand wire which behaves closer to sold wire. Try using tin plated stranded wire first and then go to Litz wire if you need to go to a lower delay or have microprocessors to analyze the RX signal like Minelab does.

Bottom line: As the target detection delay gets lower, the elimination of the potential to induce eddy currents into the coil wire becomes more critical.

I hope this helps?

Joseph J. Rogowski

[jladre]

Thanks for that informative comment joseph r.