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Amorphous metal tape

Started by Clive Arthur May 28, 2021
I need to make an inductor - a couple of mH at a couple of amps.  It has 
to fit in an awkward space, roughly oval toroidal and nothing off the 
shelf. Nothing I can do about the space.

So this tape - I know nothing of it except that it can be used for 
transformer cores.  Can I buy a roll and wind my own core on a former? 
Anyone used it?

-- 
Cheers
Clive

On Fri, 28 May 2021 18:10:50 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

>I need to make an inductor - a couple of mH at a couple of amps. It has >to fit in an awkward space, roughly oval toroidal and nothing off the >shelf. Nothing I can do about the space. > >So this tape - I know nothing of it except that it can be used for >transformer cores. Can I buy a roll and wind my own core on a former? >Anyone used it?
I have a spool of the stuff. I could send you some. The advantage is enormous permeability, the disadvantage is that it makes an inductor yet more labor intensive. Have you tried Coilcraft? They are helpful. Newava does custom magnetics for us and is good. Can you use a few small toroidal cores sort of bent around the available volume? Better yet, some standard parts?
On Friday, May 28, 2021 at 10:10:56 AM UTC-7, Clive Arthur wrote:
> I need to make an inductor - a couple of mH at a couple of amps. It has > to fit in an awkward space, roughly oval toroidal and nothing off the > shelf. Nothing I can do about the space. > > So this tape - I know nothing of it except that it can be used for > transformer cores. Can I buy a roll and wind my own core on a former? > Anyone used it?
I think you're talking about Metglas; some quick-quench alloys that have a non-crystalline amorphous microstructure, so cannot be usefully cold-worked or reheated without destroying its virtues. It can be produced as a thin tape, suitable for winding into toroid shape, and a crimped spool can hold it there. Presumably, a shaped core and epoxy could make an oval, but applying a winding would be a challenge (just as with any toroid). It's springy stuff (remember, you cannot anneal it to make it soft) so there's some force required to keep it together. As for getting a sample, just buy a toroid and cut off the spool; it'll unwind into a long strip . There may be some glue, though; that's a chemistry problem. Elna and Hitachi make such cores.
On 2021-05-28, Clive Arthur <clive@nowaytoday.co.uk> wrote:
> I need to make an inductor - a couple of mH at a couple of amps. It has > to fit in an awkward space, roughly oval toroidal and nothing off the > shelf. Nothing I can do about the space. > > So this tape - I know nothing of it except that it can be used for > transformer cores. Can I buy a roll and wind my own core on a former? > Anyone used it?
Roughly oval, tape wound core, sounds like R-core. But for an inductor you want a gap, and R-core (or any tape-wound core) won't give much of that SFAIK. -- Jasen.
On Fri, 28 May 2021 21:38:00 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

>On 2021-05-28, Clive Arthur <clive@nowaytoday.co.uk> wrote: >> I need to make an inductor - a couple of mH at a couple of amps. It has >> to fit in an awkward space, roughly oval toroidal and nothing off the >> shelf. Nothing I can do about the space. >> >> So this tape - I know nothing of it except that it can be used for >> transformer cores. Can I buy a roll and wind my own core on a former? >> Anyone used it? > >Roughly oval, tape wound core, sounds like R-core. > >But for an inductor you want a gap, and R-core (or any tape-wound core) >won't give much of that SFAIK.
Good point. A few tiny permalloy or kool-mu toroids could be wound in series and stuffed into an odd-shaped volume. Powdered iron if the AC current is low. "a couple of mH at a couple of amps" will be pretty big.
John Larkin wrote:
=================
> > "a couple of mH at a couple of amps" will be pretty big. >
** Should be smaller than a golf ball ( 42mm dia) ..... Phil
In article <s8rnro$moc$1@gonzo.revmaps.no-ip.org>, usenet@revmaps.no-
ip.org says...
> But for an inductor you want a gap, and R-core (or any tape-wound core) > won't give much of that SFAIK. >
Why? I thought the point of core designs was largely to minimise any gap, but I haven't been following the whole argument...
On 29/05/2021 01:56, Phil Allison wrote:
> John Larkin wrote: > ================= >> >> "a couple of mH at a couple of amps" will be pretty big. >> > > ** Should be smaller than a golf ball ( 42mm dia) > > > ..... Phil
Yes, that's about the right volume. Normally we'd use two or three stacked toroid cores, but this customer doesn't have the form factor space for that. -- Cheers Clive
 Mike Coon wrote:
  ===============
> > > But for an inductor you want a gap, and R-core (or any tape-wound core) > > won't give much of that SFAIK. > > > Why? I thought the point of core designs was largely to minimise any > gap, but I haven't been following the whole argument...
** FYI : any "gapless" magnetic core saturates very easily, losing its magnetic properties when used as an *inductor". Transformers are a different story, since primary off load currents are small. For a compact inductor that passes significant AC or DC current, a carefully sized air gap is essential. This apples to laminated steel or solid ferrite cores - but not so much to powdered iron cores as the air gap is intrinsic. Not a simple topic, bore your self to tears looking it all up. ..... Phil
 Clive Arthur wrote:
===============
> > >> "a couple of mH at a couple of amps" will be pretty big. > >> > > > > ** Should be smaller than a golf ball ( 42mm dia) > > > Yes, that's about the right volume. Normally we'd use two or three > stacked toroid cores, but this customer doesn't have the form factor > space for that. >
** IMO ought to be possible with a powdered iron bobbin and just the right turns. Loudspeaker passive x-overs often have such inductors in them. ..... Phil