Litz Wire?

[abstruse1]

I've read that Litz wire conducts high frequency much better (lower resistance, I assume) than traditional wire diameters.  Has anyone had any experience using Litz for the primaries of flybacks?

[Mads Barnkob]

Litz wire is "better" in the way that you can utilize the entire copper conductor at your given frequency. Using a single wire, the skin depth of the current, will at higher frequencies not penetrate the conductor completely, so you are "wasting" material in the middle of the conductor as its not conducting any current. It can however help dissipate or lead away heat or supply mechanical strength.

The Litz is made up of individual insulated wires, thus each is their own conductor in respect to the other wires in the bundle. In this configuration you can select a Litz wire that suits your freqency, in order to obtain 100% current penetration.

I wrote about skin depth in a easy to understand way here: https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/busbar-and-primary-circuit/ Scroll down a bit.

I have used litz wire for flyback primaries, but for short runs like in experiments, normal machine tool wire will work just fine. It is not a problem for me if it gets hot to touch, as long as the insulation does not melt.

[abstruse1]

So, Mads, do you think Litz primary wire will transfer more of the power (current or voltage) from the driver than solid wire?

[Mads Barnkob]

So, Mads, do you think Litz primary wire will transfer more of the power (current or voltage) from the driver than solid wire?

There can only be a difference in terms of heat losses, so if the solid wire primary does not get too hot to touch, then the difference will be miniscule.

[NerdlabsMadScience]

yea litz wire is great for high frequency its pretty easy to make yourself out of regular magnet wire which is way cheaper than buying litz wire

[davekni]

yea litz wire is great for high frequency its pretty easy to make yourself out of regular magnet wire which is way cheaper than buying litz wire

Yes, I frequently make my own litz wire, as for my DRSSTC primary.  However, home-made litz wire is rarely quite as good as commercial litz wire.  To be ideal, each strand of litz wire needs to have equal lengths at all locations through the wire cross-section.  Otherwise some strands encompass more magnetic field that other strands, causing mismatched voltage and circulating currents.  Home-made litz is still much better than solid wire for many applications.  (Large wire for large line-frequency transformers is often referred to as "continuously transposed" rather than litz, made of separately insulated rectangular conductors.)

[abstruse1]

Thanx, guys.

[klugesmith]

"Continuously transposed"

Have any of you noticed HV transmission towers at which the three phases are transposed?

I think they always do this every so many kilometers,
so the 3 phases have equal exposure to being in the middle position, and to being closest to the ground.

Could dig out some pictures, by searching my archives or searching the Internet.

[klugesmith]

It _is_ called transposition. Nice discussion and picture here: https://electronics.stackexchange.com/questions/83152/how-do-transposition-towers-in-transmission-lines-work

[davekni]

It _is_ called transposition.

My dad was a power distribution engineer, though for more local distribution within campuses than long-distance transmission lines.  He told me that transposition was to reduce average coupling (couple all phases equally so vector sum adds to zero) to any lower-voltage lines that happen to be parallel, especially phone wires.  Presume that was more important long ago when phone wires were individually strung.  It makes sense that coupling to ground should be canceled too.  So still useful today.

Slightly related to transposing conductors of the same phase (same conductor) within litz wire.  It is to average out coupling.  In litz wire case, it is averaging out coupling across non-uniform magnetic field within a winding.