Litz Wire

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  • Last Post 16 May 2022
Gandalf posted this 03 May 2022

Litz wire

Litz wire is a particular type of multistrand wire or cable used in electronics to carry alternating current (AC) at radio frequencies. The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz.[1] It consists of many thin wire strands, individually insulated and twisted or woven together, following one of several carefully prescribed patterns[2][better source needed] often involving several levels (groups of twisted wires are twisted together, etc.). The result of these winding patterns is to equalize the proportion of the overall length over which each strand is at the outside of the conductor. This has the effect of distributing the current equally among the wire strands, reducing the resistance. Litz wire is used in high Q inductors for radio transmitters and receivers operating at low frequencies, induction heating equipment and switching power supplies.

How Litz wire works

One technique to reduce the resistance is to place more of the conductive material near the surface where the current is by replacing the wire with a hollow copper tube. The larger surface area of the tube conducts the current with much less resistance than a solid wire with the same cross-sectional area would. The tank coils of high power radio transmitters are often made of copper tubing, silver plated on the outside, to reduce resistance. However tubing is not flexible and requires special tools to bend and shape.

Litz wire is another method, which employs a stranded wire with individually insulated conductors (forming a bundle). Each thin conductor is less than a skin-depth, so an individual strand does not suffer an appreciable skin effect loss. The strands must be insulated from each other—otherwise all the wires in the bundle would short together, behave like a single large wire, and still have skin effect problems. Furthermore, the strands cannot occupy the same radial position in the bundle over long distances: the electromagnetic effects that cause the skin effect would still disrupt conduction. The weaving or twisting pattern of the wires in the bundle is designed so that the individual strands are on the outside of the bundle for a distance (where the EM field changes are smaller and the strand sees low resistance), and are on the inside of the bundle for a distance (where the EM field changes are the strongest and the resistance is higher). If strands have a comparable impedance, current is distributed equally among every strand within the cable. This allows the interior of the litz wire to contribute to the overall conductivity of the bundle.

Another way to explain the benefit of litz braiding is as follows: the magnetic fields generated by current flowing in the strands are in directions such that they have a reduced tendency to generate an opposing electromagnetic field in the other strands. Thereby, for the wire as a whole, the skin effect and associated power losses when used in high-frequency applications are reduced. The ratio of distributed inductance to distributed resistance is increased, relative to a solid conductor, resulting in a higher Q factor at these frequencies.

 

Examples of skin depth in copper wire at different frequencies

  • At 60 Hz, the skin depth of a copper wire is about 7.6 millimetres (0.30 in).
  • At 60,000 Hz (60 kHz), the skin depth of copper wire is about 0.25 millimetres (0.0098 in).
  • At 6,000,000 Hz (6 MHz) [5] the skin depth of copper wire is about 25 micrometres (0.00098 in).

https://en.wikipedia.org/wiki/Litz_wire


https://www.hflitzwire.com/litz-wire-calculation-and-design/

“All we have to decide is what to do with the time that is given us.“

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Gandalf posted this 03 May 2022

Litz wire

Litz wire is a particular type of multistrand wire or cable used in electronics to carry alternating current (AC) at radio frequencies. The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz.[1] It consists of many thin wire strands, individually insulated and twisted or woven together, following one of several carefully prescribed patterns[2][better source needed] often involving several levels (groups of twisted wires are twisted together, etc.). The result of these winding patterns is to equalize the proportion of the overall length over which each strand is at the outside of the conductor. This has the effect of distributing the current equally among the wire strands, reducing the resistance. Litz wire is used in high Q inductors for radio transmitters and receivers operating at low frequencies, induction heating equipment and switching power supplies.

How Litz wire works

One technique to reduce the resistance is to place more of the conductive material near the surface where the current is by replacing the wire with a hollow copper tube. The larger surface area of the tube conducts the current with much less resistance than a solid wire with the same cross-sectional area would. The tank coils of high power radio transmitters are often made of copper tubing, silver plated on the outside, to reduce resistance. However tubing is not flexible and requires special tools to bend and shape.

Litz wire is another method, which employs a stranded wire with individually insulated conductors (forming a bundle). Each thin conductor is less than a skin-depth, so an individual strand does not suffer an appreciable skin effect loss. The strands must be insulated from each other—otherwise all the wires in the bundle would short together, behave like a single large wire, and still have skin effect problems. Furthermore, the strands cannot occupy the same radial position in the bundle over long distances: the electromagnetic effects that cause the skin effect would still disrupt conduction. The weaving or twisting pattern of the wires in the bundle is designed so that the individual strands are on the outside of the bundle for a distance (where the EM field changes are smaller and the strand sees low resistance), and are on the inside of the bundle for a distance (where the EM field changes are the strongest and the resistance is higher). If strands have a comparable impedance, current is distributed equally among every strand within the cable. This allows the interior of the litz wire to contribute to the overall conductivity of the bundle.

Another way to explain the benefit of litz braiding is as follows: the magnetic fields generated by current flowing in the strands are in directions such that they have a reduced tendency to generate an opposing electromagnetic field in the other strands. Thereby, for the wire as a whole, the skin effect and associated power losses when used in high-frequency applications are reduced. The ratio of distributed inductance to distributed resistance is increased, relative to a solid conductor, resulting in a higher Q factor at these frequencies.

 

Examples of skin depth in copper wire at different frequencies

  • At 60 Hz, the skin depth of a copper wire is about 7.6 millimetres (0.30 in).
  • At 60,000 Hz (60 kHz), the skin depth of copper wire is about 0.25 millimetres (0.0098 in).
  • At 6,000,000 Hz (6 MHz) [5] the skin depth of copper wire is about 25 micrometres (0.00098 in).

https://en.wikipedia.org/wiki/Litz_wire


https://www.hflitzwire.com/litz-wire-calculation-and-design/

“All we have to decide is what to do with the time that is given us.“

Gandalf posted this 03 May 2022

Where was used litz wire


Don Smith / Tom Bearden

 

“All we have to decide is what to do with the time that is given us.“

cd_sharp posted this 08 May 2022

Guys, this page is suggesting that coils wires lengths are calculated based on the wavelength formula:

wavelength = wave speed / frequency,

wavelength in meters

wave speed in meters per second

frequency in cycles per second.

Don Smith used this relationship.

Excellent finding, Gandalf! Stay strong!

Vidura posted this 08 May 2022

Dear friends, if I may add some information about the topic, in electronic engineering it is Sayed that the mean reason for using litz wire is to reduce the skin effect, and thus increase the Q factor of the inductor. Regarding the formula for frequency , wavelength and propagation velocity it is important to know, that the latter is defined by the dielectric constant of the material surrounding the conductor. For example air with a constant of~ 1 is near 300000000m/sec, in the case of PVC insulated wire it slows down to ~180000000m/s. This is the reason for eventual errors in calculating .

Vidura

cd_sharp posted this 09 May 2022

Vidura, this is excellent information. If I'm using copper enameled wire, I should still be using 300000000m/sec or I should try finding this constant for the dielectric enamel? Maybe there are books covering this topic.

Stay strong!

Vidura posted this 12 May 2022

Hey CD, it is rare to find information about the propagation velocity in textbooks, as usually it is assumed to be always near 300000000m/s. I believe thee is a difference due to the enamel coating. It could be measured relatively easy with the scope. Ideally an extended wire should be used to keep out the effect of interwinding capacitances and inductance.

Vidura.

Vidura

cd_sharp posted this 15 May 2022

Hey, guys

Vidura, I think this experiment gives us the answer:

I may be wrong, but he is probably using enameled copper wire.

In the above experiment, the current travels at the speed of light. This means the EM wave propagates at the speed of light.

Maybe someone else did an experiment using another type of insulation. I'll be reading more on the subject.

Stay strong!

Fighter posted this 16 May 2022

Hi Cd_Sharp,

I fixed the video.

For YouTube videos just placing the link of the video as text will work, there is no need to use the video button.

Regards,

Fighter

"If you want to find the secrets of the universe, think in terms of energy, frequency and vibration."
Nikola Tesla
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