On Sun, 01 Dec 2013 14:15:05 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:
>On Sun, 01 Dec 2013 13:50:07 -0700, Neon John <no@never.com> wrote:
>
>>> ..anip...waaay too much excellent data
>was that F, or C hope it was F 71C is hot enough, I can't even hold onto
>50C items if more than a few pounds.
yes, deg F.
>
>Yes, think that was the paper. The premise sounded so good always wondered
>if made much difference. Glad you went to the effort. perhaps the cable
>was too tight and the O2 couldn't get down in there. Like a gas seal from
>the pressure. Wonder what would have happened *if* you could have used
>pre-dulled copper strands THEN spun into a cable.
Dunno. Copper oxide is a semiconductor (re: copper oxide rectifiers)
so I suspect that it just wouldn't work very well.
I never had an appreciation of just how good Litz wire is at these
moderate frequencies until I got involved in induction heater design.
John
John DeArmond
http://www.neon-john.comhttp://www.fluxeon.com
Tellico Plains, Occupied TN
See website for email address
Reply by Tim Williams●December 1, 20132013-12-01
"Bill Sloman" <bill.sloman@gmail.com> wrote in message
news:6c985074-781a-47ab-b55d-ac80d70574bd@googlegroups.com...
> They don't have to simply twist the seven bundles in one hit. If you
> twisted
> a three strand bundle and a separate four strand bundle and then twisted
> those two bundles together you'd get a rather better effect, if less
> good
> packing.
Could, but you'd have to insist that they do it that way, and you'd be
paying extra for it. Litz is built in batches, so they'd have to go out
of their way to make the 3x, and seperately make the 4x. Then as the
final step, braid those to make the 2x. Which might not even be possible
because of the asymmetry.
Most of NEWT's catalog stuff shows multipliers of 3 and 5, on all bundles
except the very first bundle, which might be 3 to 50+ strands, twisted.
The second bundle (first braid) might be 7x, but I don't think they
recommend any subsequent braids be 7x or more. Really big cable, in the
10k strand range, looks like 5x5x5x5x16. They just use more steps to get
bigger cable.
Tim
--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com
Reply by Tim Williams●December 1, 20132013-12-01
"P E Schoen" <paul@peschoen.com> wrote in message
news:l7f2de$te4$1@dont-email.me...
>> But I mean a toroidally shaped, hollow core, with the winding inside.
>
>I think I see what you mean - sort of an idealized pot core where the
>magnetic material totally encloses the coil. ...
Yes! That. It can be so hard to describe things sometimes...
>> This is the closest thing I can find. But it can also be made from a
>> continuous steel winding, which should give better performance than
>> cut strips (which sounds like a lazy way to do it).
>> http://www.teslauniverse.com/nikola-tesla-article-the-swinburne-hedgehog-transformer
>
>I can't quite grasp the concept, other than it seems like a rod core
>coupled inductor.
Well, if it were a rod, it wouldn't be folded over. Consider the
"idealized wound pot core", but run a cutting wheel around the periphery
so you get strands splayed out, instead of a continuous winding. Then
clamp the strands back into place. That's roughly what Swinburne had, at
least in my mind. Just with longer strips so the ends overlap, which will
help significantly with airgap.
Tim Allen grunt "Ohh Ohh Ohh!" :-)
Only thing better would be using solid copper pipe for the innie and
outie. And brazed to end plates. Coaxial winding. That much meat would
probably be good for continuous duty, heh.
Coaxial windings on toroids work great at high frequencies, too; easy to
make a ferrite transformer of moderate size (as ferrite transformers go,
not as breaker testers go :) ) with bandwidth 50MHz and up, with high
turns ratio.
Tim
--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com
Reply by RobertMacy●December 1, 20132013-12-01
On Sun, 01 Dec 2013 13:50:07 -0700, Neon John <no@never.com> wrote:
was that F, or C hope it was F 71C is hot enough, I can't even hold onto
50C items if more than a few pounds.
Yes, think that was the paper. The premise sounded so good always wondered
if made much difference. Glad you went to the effort. perhaps the cable
was too tight and the O2 couldn't get down in there. Like a gas seal from
the pressure. Wonder what would have happened *if* you could have used
pre-dulled copper strands THEN spun into a cable.
Reply by Neon John●December 1, 20132013-12-01
On Sun, 01 Dec 2013 06:13:02 -0700, RobertMacy
<robert.a.macy@gmail.com> wrote:
>Somewhere there is an IEEE paper [I think] showing how multistranded cable
>is a 'poor' man's Litz wire. The better performance of multistrand versus
>solid is attributed to the poor 'cross-conductivity' between strands. It
>seems the stranding vectorizes the conductivity. From memory they
>presented data comparing losses between solid and stranded with the same
>copper cross section.
I have that paper or one very similar. In it the author was testing
the difference between Litz and finely stranded welding cable. His
claim was that the oxide coating on the individual strands was enough
to eliminate adjacent eddy current flow.
Sounded reasonable so I tested the theory at 80kHz and about 60 amps
using a Roy induction heater. 60 amps should not significantly heat
$4 wire and in fact, the Litz wire the transformer is wound with
stayed quite cool, as did the 4 ft long extension cables that I made
for the test. The welding cable, OTOH, got too hot to touch. I don't
recall the exact figures but it was in the 160 deg range when
equilibrium was reached.
So I set up to enhance the oxide theory. I made a fixture so that I
could flow oxygen into one end of the welding cable and let it escape
the other end. Then the pieces were placed in an oven and baked at
400 deg F for several days.
At the end of the run, cutting into the insulation showed the strands
to have a nice uniform dull oxide coating. Unfortunately, it only
made about a 10% improvement over the standard welding cable.
We use welding cable as output leads on the Roy heater for cost and
durability reasons and it does get hot. Our Litz wire manufacturer
will extrude a neoprene jacket over #4 equiv Litz wire if we'll buy a
certain minimum quantity. We're about to do that.
John
John DeArmond
http://www.neon-john.comhttp://www.fluxeon.com
Tellico Plains, Occupied TN
See website for email address
Reply by Bill Sloman●December 1, 20132013-12-01
On Saturday, 30 November 2013 15:10:27 UTC+11, Tim Williams wrote:
> "P E Schoen" <paul@peschoen.com> wrote in message=20
> news:l7bb4h$fmm$1@dont-email.me...
> >
> > I checked the website and they also offer 7x52/38 which is equivalent t=
o #10 AWG and rated for about 17 amps at 600 CM/A (3.3 A/mm^2). It's list=
ed at $1.13 while the larger size 7x7x52/38 is $8.31. That should be good f=
or 17*7=3D 119 amps which is equivalent to #4 at 350 CM/A (which may be to=
o much for continuous duty in a transformer core).
>=20
> Strange...
>=20
> Note that anything with 7 bundles is 14% useless: you get six around one =
central core, which never moves out from the center and therefore exhibits=
hugely greater resistance than the others. I've only ever seen 3 and 5x=
bundles from NEWT, but I've seen Chinese stuff that's 7-way before. Doe=
sn't make sense why anyone would make it that way, unless they simply did=
n't know how to do it properly.
They don't have to simply twist the seven bundles in one hit. If you twiste=
d a three strand bundle and a separate four strand bundle and then twisted =
those two bundles together you'd get a rather better effect, if less good p=
acking.
--=20
Bill Sloman, Sydney
Reply by RobertMacy●December 1, 20132013-12-01
On Sat, 30 Nov 2013 05:24:13 -0700, Tim Williams <tmoranwms@charter.net>
wrote:
>> ...snip...
> You can of course apply the Litz trick to foil, but you don't have any
> free lunch; the geometry reduction is still required whether putting
> together a bunch of strips or strands. Ten strips woven together will
> have less resistance than a single strip of the same width and
> thickness, but higher than 1/10th of an isolated strip that size. I
> know of at least one company that claims to have some sort of foil
> technology that reduces Rac like Litz, presumably doing some kind of
> weave. Tempting to buy a bigass custom part from them just to take it
> apart and look, see how they put the stuff together. I can't imagine
> it's all that easy to make, considering there are only two US companies
> making the round stuff as is.
>
> Tim
>
Somewhere there is an IEEE paper [I think] showing how multistranded cable
is a 'poor' man's Litz wire. The better performance of multistrand versus
solid is attributed to the poor 'cross-conductivity' between strands. It
seems the stranding vectorizes the conductivity. From memory they
presented data comparing losses between solid and stranded with the same
copper cross section.
Very interesting article, because I had always thought that solid versus
stranded didn't matter much. But, the paper is good news since it's easier
to wrap 10 strands of 18 Awg than a single strand of 8Awg. The only
'overhead' appears to be similar to stacking factor - in that you can't
completely fill the winding area.
Reply by P E Schoen●December 1, 20132013-12-01
"Tim Williams" wrote in message news:l7ea2g$trv$1@dont-email.me...
> R-cores are the rectangular equivalent, often used in line =
transformers=20
> (two bobbins, cut core).
> Heh, there's a three phase equivalent, too.
> =
http://www05.abb.com/global/scot/scot252.nsf/veritydisplay/03899f0fbab607=
e1c1257b160029b944/$file/A2_306_Cigre2012_1LAB000507_Benefits%20of%20tran=
sformers%20based%20on%20triangular%20wound%20core%20configurations.pdf
That's interesting. Some time ago we had a transformer company design a=20
three phase high current transformer, with 3x480V primaries and =
3x20V@5000=20
amp secondaries. We used water-cooled Semicron "brick" rectifiers. The =
test=20
set was delivered to the customer (ABB, IIRC) for use in testing high=20
current DC breakers used in nuclear plants. But the rectifiers soon =
failed,=20
and I had to go on site with a technician and a bunch of new =
"reinforced"=20
rectifiers designed for high pulse currents. They were testing at =
upwards of=20
50,000 amps.
> But I mean a toroidally shaped, hollow core, with the winding inside.
I think I see what you mean - sort of an idealized pot core where the=20
magnetic material totally encloses the coil. It seems that it could be =
built=20
like a conventional toroid but using copper magnet wire for the core, =
and=20
then spiral wrapping silicon steel wire or narrow tape around it like a=20
spring (or just like the copper windings are done on a toroid). The only =
problem would be accessing the windings inside the core, but it could be =
wound only to perhaps 355 degrees and the leads could come out the 5 =
degree=20
opening.
> This is the closest thing I can find. But it can also be made from a=20
> continuous steel winding, which should give better performance than
> cut strips (which sounds like a lazy way to do it).
> =
"P E Schoen" <paul@peschoen.com> wrote in message
news:l7duqb$do6$1@dont-email.me...
>> Wire core toroids do exist, and work. The coils can be wound around
>> the core, as a traditional (ring core) toroid, or the coils can be ring
>> shaped (as in a pot core construction), and the magnetic core wound
>> around that toroidally. They are very rarely seen... mostly as science
>> projects I guess? Does anyone know if anyone actually produced
>> transformers with this method, perhaps very early models?
>
>Some time ago I remember finding such cores. I think it was a Chinese
>company. But I have been unable to find anything recently. I did find a
>source of true toroidal cores with a circular cross-section which is
>perhaps 15% more efficient:
>http://www.alphacoredirect.com/contents/en-us/d2_ocores.html
"Tim Williams" wrote in message news:l7cm8j$89r$1@dont-email.me...
> The analogy is no accident -- consider the laminations, which carry an =
> axial field (i.e., parallel to the plates) and a transverse eddy =
current=20
> (looping around the perimeter; in essence, breaking up and stretching =
that=20
> perimeter by sawing the core into laminations increases the =
perimeter's=20
> resistance, decreasing eddy currents). Current flowing down a wire is =
> axial, with a transverse magnetic field -- it's a 90 degree analogy, =
but=20
> the same right hand rule is at work, generating phase shift, loss and=20
> shielding effects.
> Presumably, braided steel cable would make excellent "mag-Litz", but =
in=20
> the same way it's difficult to make a connection to Litz wire (a =
soldered=20
> lug sucks all that evenly-distributed current onto its surface..), =
it's=20
> rather difficult to make a solid loop (with little airgap) of steel =
wires.=20
> (One would hope to trace a given strand through the cable and somehow =
weld=20
> its ends together to eliminate airgap, doing this for the entire =
cable...)
> Wire core toroids do exist, and work. The coils can be wound around =
the=20
> core, as a traditional (ring core) toroid, or the coils can be ring =
shaped=20
> (as in a pot core construction), and the magnetic core wound around =
that=20
> toroidally. They are very rarely seen... mostly as science projects I =
> guess? Does anyone know if anyone actually produced transformers with =
> this method, perhaps very early models?
Some time ago I remember finding such cores. I think it was a Chinese=20
company. But I have been unable to find anything recently. I did find a=20
source of true toroidal cores with a circular cross-section which is =
perhaps=20
15% more efficient:
http://www.alphacoredirect.com/contents/en-us/d2_ocores.html
Paul=20