Transformer design question -- what does 'strand' mean

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Could some electronics guru please clarify  
this a bit ? Going over Col. Lyman's classic  
text on inductor/transformer design (especially switching transformers) I came upon the term 'strands'. For example, the total number of  
turns is 40, and the number of strands is 2.  
What wxactly does this mean ?  I am afraid my concepts are a bit rusty at present, as I have  
been out of touch with this yopic for a while.  
Thanks in advance for your help.  

Re: Transformer design question -- what does 'strand' mean
On 29-Jul-15 12:32 PM, snipped-for-privacy@gmail.com wrote:
Quoted text here. Click to load it


Two lacquered conductors side by side = 2 strands?

Re: Transformer design question -- what does 'strand' mean
wrote:

Quoted text here. Click to load it

We used to call that "two-in-hand".  Two wires held as one, wrapped on
the bobbin 40 "turns".
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer design question -- what does 'strand' mean
On Wed, 29 Jul 2015 08:24:35 -0700, Jim Thompson

Quoted text here. Click to load it

As Phil pointed out it's called Bi-filar windings.
<https://en.wikipedia.org/wiki/Bifilar_coil

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

Re: Transformer design question -- what does 'strand' mean
On Wed, 29 Jul 2015 11:34:38 -0400, Martin Riddle

Quoted text here. Click to load it

I had a technician who could _braid_ three or more "strands" then wind
the transformer.  We ultimately went to using Litz.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer design question -- what does 'strand' mean
On 29/07/2015 16:39, Jim Thompson wrote:

<snip>

Quoted text here. Click to load it

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
--  
Syd

Re: Transformer design question -- what does 'strand' mean
wrote:

Quoted text here. Click to load it

Yep.  I still have some G-job breadboards around that have braided
+/-/gnd from the breadboard to the power supply.

I can even manage braiding three myself... my technician could easily
do five or more ;-)
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer design question -- what does 'strand' mean
wrote:

Quoted text here. Click to load it

Oh, go on..  

Quoted text here. Click to load it

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


--  
Best regards,  
Spehro Pefhany
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer design question -- what does 'strand' mean
On Wed, 29 Jul 2015 17:16:20 -0400, Spehro Pefhany

Quoted text here. Click to load it

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

Cheers

Re: Transformer design question -- what does 'strand' mean
On Wed, 29 Jul 2015 17:16:20 -0400, Spehro Pefhany

Quoted text here. Click to load it
[snip]

Braiding three is so easy even I can do it ;-)
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer design question -- what does 'strand' mean
"Spehro Pefhany"  wrote in message  
Quoted text here. Click to load it


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

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
We've slightly trimmed the long signature. Click to see the full one.
Re: Transformer design question -- what does 'strand' mean
snipped-for-privacy@gmail.com wrote:

Quoted text here. Click to load it

** A "strand" is a single filament or wire.  

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  


Re: Transformer design question -- what does 'strand' mean
On Wednesday, 29 July 2015 14:33:03 UTC+10, snipped-for-privacy@gmail.com  wrote:
Quoted text here. Click to load it
 came upon the term 'strands'. For example, the total number of  
Quoted text here. Click to load it
 present, as I have  
Quoted text here. Click to load it

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

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

http://www.newenglandwire.com/products/litz-wire-and-formed-cables/

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.

--  
Bill Sloman, Sydney

Site Timeline