Litz wire

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Litz wire

madscientistatlarge
If I make my own litz wire, for a SMPS, can/should I twist the secondary in with the primary (different colors)?  Presumably this would increase coupling?  Specifically I was going to mix the windings in the first bundle before bundling those together.  Since peak secondary current is 3X peak primary current I was thinking 3 secondary wires twisted with one primary for the initial bundle (and then several of those twisted and bundling that bundle).  This would be a SEPIC topology.  I'm only making a few of these and this kind of simple work is meditative for me so I don't mind the time (I used to enjoy making cables at work, uses just enough brain power to distract from all else).


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Re: Litz wire

Ryan O'Connor
>From what I understand of magnetic flux, it wouldn't make a difference. The
primary doesn't get transferred ("coupled") to the secondary directly. It's
energy gets stored in the magnetic field and then induced into the
secondary coil.

On Tue, 3 Nov 2020 at 22:19, madscientistatlarge <
[hidden email]> wrote:

> If I make my own litz wire, for a SMPS, can/should I twist the secondary
> in with the primary (different colors)?  Presumably this would increase
> coupling?  Specifically I was going to mix the windings in the first bundle
> before bundling those together.  Since peak secondary current is 3X peak
> primary current I was thinking 3 secondary wires twisted with one primary
> for the initial bundle (and then several of those twisted and bundling that
> bundle).  This would be a SEPIC topology.  I'm only making a few of these
> and this kind of simple work is meditative for me so I don't mind the time
> (I used to enjoy making cables at work, uses just enough brain power to
> distract from all else).
>
>
> Sent with ProtonMail Secure Email.
>
>
>
> --
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Re: Litz wire

madscientistatlarge
In SEPIC topology energy is constantly being transferred (both when the primary is energized and when it's not), Which reduces the ripple currents (in both primary and secondary).  It's one of the reasons I chose that topology.  FYI, primary duty cycle will be 75% on, 25% off.  I'll have to model it to get the actual current ripple.  The cap between primary/secondary also transfers some of the energy (has to be nonpolarized, ceramic works good in this application).  Spice simulation and measured performance should be interesting.  Haven't used spice before but I only have to simulate the power path, not the controller.  First time I've saturated my intellect in years, it feels good!


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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, November 3, 2020 3:13 AM, Ryan O'Connor <[hidden email]> wrote:

> > From what I understand of magnetic flux, it wouldn't make a difference. The
>
> primary doesn't get transferred ("coupled") to the secondary directly. It's
> energy gets stored in the magnetic field and then induced into the
> secondary coil.
>
> On Tue, 3 Nov 2020 at 22:19, madscientistatlarge <
> [hidden email]> wrote:
>
> > If I make my own litz wire, for a SMPS, can/should I twist the secondary
> > in with the primary (different colors)? Presumably this would increase
> > coupling? Specifically I was going to mix the windings in the first bundle
> > before bundling those together. Since peak secondary current is 3X peak
> > primary current I was thinking 3 secondary wires twisted with one primary
> > for the initial bundle (and then several of those twisted and bundling that
> > bundle). This would be a SEPIC topology. I'm only making a few of these
> > and this kind of simple work is meditative for me so I don't mind the time
> > (I used to enjoy making cables at work, uses just enough brain power to
> > distract from all else).
> > Sent with ProtonMail Secure Email.
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>
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Re: Litz wire

Brooke Clarke
In reply to this post by madscientistatlarge
Hi Mad:

When you wind wire on a core the first layer is tightly coupled to the core.  The next layer is less coupled because
there's some area that's not core, i.e. it's copper wire which is not core.  This is why you commonly see a single layer
winding on cores.

So . . . if you combine the primary and secondary into one cable it will be larger in diameter and not be as tightly
coupled to the core as would be the case with two separate windings.
PS I've bought a number of different Litz (and probe) wires from http://www.coonerwire.com/litz-wire/
Note they have a variety of weaves for the Litz.

--
Have Fun,

Brooke Clarke
https://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------

> Date: Tue, 03 Nov 2020 09:17:59 +0000
> From: madscientistatlarge <[hidden email]>
> Subject: Litz wire
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> If I make my own litz wire, for a SMPS, can/should I twist the secondary in with the primary (different colors)?  Presumably this would increase coupling?  Specifically I was going to mix the windings in the first bundle before bundling those together.  Since peak secondary current is 3X peak primary current I was thinking 3 secondary wires twisted with one primary for the initial bundle (and then several of those twisted and bundling that bundle).  This would be a SEPIC topology.  I'm only making a few of these and this kind of simple work is meditative for me so I don't mind the time (I used to enjoy making cables at work, uses just enough brain power to distract from all else).

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Re: Litz wire

RussellMc
In reply to this post by madscientistatlarge
A secondary issue (pun noted) is the potential between windings and wire
insulation. Whether this matters depends on application.

In some situations the voltage between winding layers on the same winding
can be large enough for insulation breakdown to become a consideration.
With primary and secondary windings and different voltages with may become
a more significant factor.
In the SEPIC topology primary: secondary isolation is not an issue, but in
an isolated converter the wire insulation would be a (maybe the) primary :
secondary isolation factor.


Russell

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