----- Original Message -----
From: "Tom Rauch" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Friday, May 17, 2002 11:17 AM
Subject: LF: Re: [Lowfer] RE: litz wire
> Hi Bill & Group,
>
> I believe why Litz wire has such a low AC resistance
> is because each strand is insulated and when soldered
> together you get the parallel resistance of each of
> the strand of insulated wire. With uninsulated,
> stranded wire you may have the same current carrying
> capacitiy but you more than likely have a higher
> resistance because all the strands are in contact with
> one another & the current path will be through all the
> contacts that offer the least resistance but better
> than solid wire because of the increase perimeter
> length.
I'm a little surprised the measured conductor resistance a loop was
significantly reduced with Litz wire compared to solid wire with the
same size and same insulation.
Litz wire *sometimes* offers higher Q in multilayer coils because it
reduces eddy currents in the wire as flux from adjacent turns cut the
cross section of the wire.
I have an engineering text that goes into details about Litz wire. It
states that Litz wire reduces eddy currents when significant flux
cuts the cross-section of a wire.
Of course eddy currents would be reduced at the expense of increased
unit resistance for a given physical conductor size, since some
current carrying conductor area is replaced with insulation.
Litz wire can also increase dielectric losses, but any change in
dielectrics where the electric field between conductors is very
intense can do that. It depends on the insulation used in the non-
Litz wire, and the insulation used in the Litz wire.
I believe the textbook description I have is correct, because I've
measured Q of hundreds of inductors and have sometimes found Litz
wire an improvement in ~ 50-500kHz systems using multilayer coils or
transformers (like switching supplies operating in the 100kHz range,
using transformers with large high-current conductors).
On the other hand, I've *never* measured a case where it improved Q
or reduced losses in solenoid or single conductor applications at any
frequency. It has actually caused problems above 1MHz when used in
high current leads (that had to be flexed, so I thought Litz wire was
a good choice).73, Tom W8JI
This is what I have been saying all along. Litz wire is not normally needed
for most of the projects discussed on here recently. Good multi strand
copper wire 1.5 - 6mm insulated in teflon is more convenient to use and
under some circumstances for large single turn loops and single layer
loading inductors is probably better. In fact large diameter hollow copper
tube is probably to be preffered.
Litz wire was used years ago for multi layer LW and MW coils where there
could be an advantage. The Decca coils were multi layer inductors and met
the requirements at the time, hardly state of the art by todays methods.
I have wound a loading coil using decca 729 strands litz and another 2.5mm
teflon insulated wire one and compared results. On air measurements and
reports are identical, regardless of what theory dictates.
The choice is yours.
73 de Mal/G3KEV
[email protected]
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