Transformer design question -- what does 'strand' mean

Two lacquered conductors side by side = 2 strands?

So, the author is referring to a form of bi-filar winding with the two wires joined at each end. Usually this is done to reduce I squared R loss due to skin effect.

.... Phil

came upon the term 'strands'. For example, the total number of

present, as I have

To echo Phil Allison, the strands might be individual filaments of lacquere d copper within a length of Litz wire.

Litz wire usually offers more than two strands per bundle. The weaving of t he individual strands into the bundle needs care - each wire needs to inter cept the same flux, averaged over the length of the winding, so simple twis ting won't deliver the desired effect.

We used to call that "two-in-hand". Two wires held as one, wrapped on the bobbin 40 "turns". ...Jim Thompson

As Phil pointed out it's called Bi-filar windings.

I don't see why Lyman's book doesn't point that out. Also, different core mfg's seem to present data differently than what is in that book. I usually refer to the mfg app notes.

The Burr-Brown transformer presentation notes are the best.

Cheers

I had a technician who could _braid_ three or more "strands" then wind the transformer. We ultimately went to using Litz. ...Jim Thompson

Braiding three strands is easy if you ever had a significantly older sister with long hair.

It's also a good way to take mains live/neutral/earth from a power inlet onto a board, as it's both pretty and self supporting.

Cheers

Yep. I still have some G-job breadboards around that have braided

I can even manage braiding three myself... my technician could easily do five or more ;-) ...Jim Thompson

Oh, go on..

Some of the 'Litz' wire sold seems to be just twisted rather than properly braided.

My understading is that it is 'twisted' but each strand is the same lenght.

Cheers

Braiding three is so easy even I can do it ;-) ...Jim Thompson

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I don't think I've seen any that is braided. Even the big guys (e.g., NEWT) twist bundles of bundles.

Although you can get flat or tubular weave constructions, which are helpful if you need to ground something with low inductance, or want to do something like high current coax (unfortunately, Litz buys you no improvements in characteristic impedance of such an assembly).

It's important that odd-packing numbers be used (usually 3 and 5, except for the first bundles which might contain tens, even hundreds of individual strands), and full-packing numbers be avoided (like 7 or 19). Many times I've seen Chinese stock, carelessly made in such manners (possibly to maximize weight or cross section with a minimum of bundles), where you can clearly see a center core is surrounded by six bundles; that core isn't going to carry any current whatsoever.

Tim