Litz wire

[Tim Williams]

Flat strip conductors negate skin effect in a similar manner as that of
a Litz wire configuration. The main problem with using it as wire is the
amount of space it takes up on a bobbin per turn. That makes it only
practical used as a hook-up link, or inter-node connection link between
points in a chassis.

Not really... I'm going to use 1.00 x 0.040" copper strap on a high amp
transformer I'm planning. 5V 100A in two turns.

Tim

 

[life imitates life]

Not really... I'm going to use 1.00 x 0.040" copper strap on a high amp
transformer I'm planning. 5V 100A in two turns.

Tim

Yes, low turn counts are possible, and it is good for that, but it is
not good for any high turns count app. There is square and flat wire,
but it is far narrower than the media in this thread refers to.

It is used in speaker coil bobbins too.

 

[E]

Not really... I'm going to use 1.00 x 0.040" copper strap on a high amp
transformer I'm planning. 5V 100A in two turns.

Tim

I have seen that kind of copper foil conductors used in some ATX power
supplies.
Don't remember how many turns as I was only interested in the ferrite core
for
other projects.

-ek

 

[amdx]

The copper rope is not long enough? We've got some discard litz wire,

but not nearly that thin or as many strands. We use it to make high Q
coils to detect the nuclear magnetic moments of protons spinning in
the Earth's B field. Frequencies a bit above 2kHz. And lots smaller
currents. Well the same coils polarize the spins, but that's 3 amps
at DC.

George H.

Hi George,
Is this used in a magnetometer?
There is a thread on rec.radio.amateur.antenna with the
subject: Carl and Jerry Magnetometer, that has a discussion
about about picking up the precession of the proton as it
returns back to alignment with the earths magnetic field.
I found it very interesting, probably because I knew zero
about the subject.
If you have anything to add to that thread, please do so.
Mike

Yeah, I'm talking about a physics teaching instrument, but they are
used professionally to measure the Earths magnetic field.

George H.

Would you care to share info about the physics teaching instrument?
Mike

 

[legg]

No, you cannot. It only works with insulated strands. Trying to come
up with an 'insulation on the fly method is just plain stupid.

buzz buzz buzz.

RL

 

[life imitates life]

buzz buzz buzz.

RL

Yes, and it would likely buzz as well. One of your legs must have
fallen off, and this stupidity is your compensation.

 

[qrk]

Who sells this stuff (without paying for miles at a time)?

I'm especially interested in stupid thick stuff, like, as large as 8AWG
equivalent. Nebraska Surplus for instance doesn't stock wire like this.

Tim

What frequency is this for. If you're under 1MHz, you're mainly
fighting proximity effect, not skin effect. To deal with proximity
effect, all you need is bunched conductors (twisted), not Litz. The
Litz wire I have come across use bunched groups twisted into a larger
bunched group. This closely approximates Litz.

 

[Tim Williams]

Let's say 200kHz-2MHz.

Tim

 

[amdx]

What frequency is this for. If you're under 1MHz, you're mainly
fighting proximity effect, not skin effect.

Hey qrk,
I haven't seen that information before, do you have anything to site
that would make me believe it?
To quote Dagmargoodboat, [At 290Khz]
"Comparing the braid to the equivalent-cross-section solid wire:

(view table in Courier font)

Winding Rac (calculated)
---------- ------------------
7 x 0,23mm 1.46*Rdc
1 x 0,608 4.29*Rdc

So, the braid was ~ 3x better.

Here are a couple of skin effect calculators.
http://daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml
http://circuitcalculator.com/wordpress/2007/06/18/skin-effect-calculator/

To deal with proximity
effect, all you need is bunched conductors (twisted), not Litz.

Ok, you need to explain what you mean by bunched conductors,
Are they insulated bunched conductors?
As stated before proximity effect is minimized by making every conductor
find itself in the same position in the bundle an equal amount of time.
Twisting may or may not do that, depends on the amount of conductors
twisted.
Mike

The Litz wire I have come across use bunched groups twisted into a
larger
bunched group. This closely approximates Litz.

Yes, "closely approximates Litz" because it would not be as good
regarding
proximity effect. It doesn't have every conductor find itself in the same
position
in the bundle an equal amount of time.
Mike

 

[life imitates life]

Are they insulated bunched conductors?

Of course they would be. Use *SOME* common sense.

 

[life imitates life]

As stated before proximity effect is minimized by making every conductor
find itself in the same position in the bundle an equal amount of time.
Twisting may or may not do that, depends on the amount of conductors
twisted.

It also depends on what he stated. If the run is short enough it makes
no difference. Lower frequencies at lower currents also have less issues
with the outward EM field push that we all know as "skin effect".

AND the mag field around each individual conductor in a bunch, whether
Litz woven or not, will be different than that of the solid, so the EM
field effect claimed to also affect non-woven bundles is not as
pronounced as you might think.

The wires in the centers of non woven bundles do NOT exhibit the same
problem that a solid does. It is several parallel fields, not a single
conduction field. Yet another reason why the effect is still realized
sans the weave. It is not 100% efficient, from that perspective, but it
DOES STILL work.

It is a fact. Get used to it.

 

[amdx]

It also depends on what he stated. If the run is short enough it makes
no difference. Lower frequencies at lower currents also have less issues
with the outward EM field push that we all know as "skin effect".

AND the mag field around each individual conductor in a bunch, whether
Litz woven or not, will be different than that of the solid, so the EM
field effect claimed to also affect non-woven bundles is not as
pronounced as you might think.

The wires in the centers of non woven bundles do NOT exhibit the same
problem that a solid does. It is several parallel fields, not a single
conduction field. Yet another reason why the effect is still realized
sans the weave. It is not 100% efficient, from that perspective, but it
DOES STILL work.

It is a fact. Get used to it.

I completely agree Jim.
I just went on a rant when qrk said,
" If you're under 1MHz, you're mainly
fighting proximity effect, not skin effect."
I don't believe that, and I think a properly sized bundle of twisted
(insulated wire)
will have a large effect over a solid wire with the same circular mils.
(as Dogmargoodboat said, 3x)
It would be interesting to find what percentage change a twisted litz
would have
over a properly braided litz. I'll bet it's under 20%.
What do you think?
Mike

 

[life imitates life]

I completely agree Jim.
I just went on a rant when qrk said,
" If you're under 1MHz, you're mainly
fighting proximity effect, not skin effect."
I don't believe that, and I think a properly sized bundle of twisted
(insulated wire)
will have a large effect over a solid wire with the same circular mils.
(as Dogmargoodboat said, 3x)
It would be interesting to find what percentage change a twisted litz
would have
over a properly braided litz. I'll bet it's under 20%.
What do you think?
Mike

So.... what a hoot. You accidentally agreed with me?

 

[amdx]

So.... what a hoot. You accidentally agreed with me?

I'd rather say you agree with me, and in that case, you sure are smart.
Mike

 

[legg]

No, you cannot. It only works with insulated strands. Trying to come
up with an 'insulation on the fly method is just plain stupid.

It doesn't really matter when, how, or why insulation between strands
is achieved and the voltage levels presented are extremely small, so
polymers are really overkill.

Note that complete isolation is not required, simply a degree of
effective isolation, most of the time, between adjacent inner and
outer stranding, as these will swap over, by design. If 80% of the
skin current is forced back into the bundle, then an effective litz
action is performed.

Litz is most called for where layering cannot be avoided. Obviously
turn and layer insulation has to be provided by something a little
more predictable. This isn't hard to do.

RL

 

[life imitates life]

It doesn't really matter when, how, or why insulation between strands
is achieved and the voltage levels presented are extremely small, so
polymers are really overkill.

It matters if it is not complete, and it touching other conductors along
the way (and it will) causes problems. If not detrimental parasitics, in
fact.

 

[JosephKK]

Why, then, does it work to make up multi-strand wire bundles for SMPS
service where the wires are just lightly twisted into a bundle? Are
these getting one part of the way there, but not all?

I had heard about the Litz wire 'gotta be a magic braid pattern', but
then I've seen all these SMPS transformers that just have almost-parallel
strands.

It is not braided in the sense that hair is braided, it is twisted in increasing
levels much like rope is. Say 3 strands twisted, in groups of 7, in supergroups
of 3, in hypergroups of 7. Though this clearly would not be optimal.

 

[qrk]

Let's say 200kHz-2MHz.

Tim

As a gross rule of thumb, proximity effect dominates under 1MHz. Above
1MHz, skin effect will come in to play. Most of my work designing
power pulse transformers is in the 50kHz to 800kHz range. Checks with
an impedance analyzer (HP 4195 and 4194) have shown that the equations
given in E.C. Snellings "Soft Ferrites" book are pretty good. E.C.
Snelling and Giles have another book on transformers. I've forgotten
the title, but it also covers proximity effect.

 

[qrk]

What frequency is this for. If you're under 1MHz, you're mainly
fighting proximity effect, not skin effect.

Hey qrk,
I haven't seen that information before, do you have anything to site
that would make me believe it?
To quote Dagmargoodboat, [At 290Khz]
"Comparing the braid to the equivalent-cross-section solid wire:

(view table in Courier font)

Winding Rac (calculated)
---------- ------------------
7 x 0,23mm 1.46*Rdc
1 x 0,608 4.29*Rdc

So, the braid was ~ 3x better.

Here are a couple of skin effect calculators.
http://daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml
http://circuitcalculator.com/wordpress/2007/06/18/skin-effect-calculator/

To deal with proximity
effect, all you need is bunched conductors (twisted), not Litz.

Ok, you need to explain what you mean by bunched conductors,
Are they insulated bunched conductors?
As stated before proximity effect is minimized by making every conductor
find itself in the same position in the bundle an equal amount of time.
Twisting may or may not do that, depends on the amount of conductors
twisted.
Mike

The Litz wire I have come across use bunched groups twisted into a
larger
bunched group. This closely approximates Litz.

Yes, "closely approximates Litz" because it would not be as good
regarding
proximity effect. It doesn't have every conductor find itself in the same
position
in the bundle an equal amount of time.
Mike

Proximity effect is little known unless you design transformers. It is
rarely taught at the uni. An excellent reference is "Soft Ferrites" by
E.C. Snelling. You can usually find this book at university libraries.
There's another book, "Ferrites for Inductors and Transformers" by
Snelling and Giles on transformer design. Soft Ferrites isn't the
easiest read, but the information towards the rear of the book has all
sorts of useful information about winding configurations. The program
"Magnetics Designer" by Intusoft also deals with proximity effect.

Frequencies under 1MHz, proximity effect is dominant. I have run the
calculations and tested transformer designs with impedance analyzers
(HP 4195 & 4194). The calculated and measured come out fairly close.

Bunched conductors are parallel insulated conductors (magnet wire)
which are twisted together, just like stranded hookup wire from
Belden, but fewer twists per inch. In a pinch, I'll make my own
bunched conductors and twist the bunch using an electric drill. For
production, I use Litz wire from MWS. I use Litz since they won't make
bunched conductors for me. Don't know why since this is considered one
bunch in a Litz construction. Since we don't make that many
transformers, the 5 pounds of wire we get will last a decade or two.

On the practical side, the bunched conductors I have made/used aren't
much different from commercial Litz wire in my tests making 5kW pulse
transformers for 400kHz service. I'm sure my office made bunched
conductors weren't perfectly in the same position at an equal time.
Holy crap, that's a lot to say! Just twist the stuff and everything
will be happy.

 

[life imitates life]

The electromagnetic argument for Litz wire is also murky, because it
relies on that dopey single-straight-wire-in-free-space derivation we
all know and love.

E X A C T L Y !

A bundle of individual EM fields from individual strands does NOT
generate a field that is the same as that of an equally sized solid
conductor.

In fact, in a solid conductor, conduction CAN be pushed to the outside
of THAT conductor. In the case of a bundle of individual conductors, the
individual EM fields generated are NOT capable of forcing ANY of the
center conductors' electrons to the outer shell of the bundle, and from
within an individual conductor, IF the push was occurring, it would only
'push' those electrons out to one side of it, but it would still be 'out'
at the skin, where it belongs.

More likely a mag wire manufacturers ploy to sell "specially
configured" spools at exorbitant prices over cost.

We could have been making our own all along.