T-Pain Is On A Boat: Re: [Electric Boats] Magnetic Circuits & The Prototype Motors

Thursday, January 3, 2013

Re: [Electric Boats] Magnetic Circuits & The Prototype Motors

Yes, sputtering ferrite dust with a printer probably wouldn't work to make lams for today's high B field magnets......I agree that the laminations really do need to be continuous metal along the flux path. Otherwise we end up simply summing a lot of little gaps.

But I can't help noticing that the guys who make flexible circuits of copper laid on mylar film seem to have solved that problem for current flow. Could something similar work for magnetic flow in the lams?

Along that same line of thought, just how thin we could go with high permeability lamination layers? I wonder if they could they be made of foil? What determines the limit? I've not done any work on that at all.

Yes, it was ferrous silt, sludge, or debris that I was referring to. It certainly builds up in the working gap. But when does it become a problem? Or does it? Has anyone seen it be a problem? A certain amount might even be an advantage since one of the effects there is to narrow the gap where the work is done.

On the other side of the ledger, we also see that ferrous sludge or particles build up anywhere that flux is leaking. That type of buildup has to be a detriment as it makes the path for flux leakage become fractionally more permeable. Might be a very small effect, though.

Magnetic sludge is one of those things to look into "someday". Fun to think about - and it wouldn't be difficult to test for effect and get some numbers - but so far I've not seen it be enough of a problem to spend time on.

Roger L.

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

From: Chris Morriss

To: electricboats@yahoogroups.com

Sent: Thursday, January 03, 2013 12:05 PM

Subject: Re: [Electric Boats] Magnetic Circuits & The Prototype Motors

In message <AD5305B63E7A40D9BDF84420C3C8276F@LENOVOBC3751E0>, Roger L
<rogerlov@ix.netcom.com> writes
>
>Yes, I agree. The increasing need for low losses in cores (& way worse
>with high freq. switching) brings up the old problem of eddy currents and
>the traditional solution of using laminated cores to control eddy currents -
>laminations which you quite properly point out are difficult to cut to shape
>in close tolerance in a home workshop. There is also the problem that
>some of the best lamination material loses some of it's goodness when it
>is stressed. Unhappily that happens when high permeability steel is
>impacted, bent, or sheared mechanically. It probably applies to water
>jetting as well, although I have solved that in the past by simply burying
>my head in the sand.....there being no better way to make them.
>

I have been told by colleagues (I design switch-mode PSUs, and Class-D
amplifiers for a living) that water jet cutting is fairly benign on
transformer steel. Avoid laser cutting it seems!

Sadly, dust-iron or ferrite materials can't take the high field strength
of NiFeB magnets (or don't have a high enough permeability), so although
an interesting idea, I'm not sure any type of printed magnetic core
materials are likely to be suitable for these type of motors (not in the
foreseeable future, though I could be wrong...)
--
Chris Morriss

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