[Boatanchors] Need magnetic shield for shaded pole motor

[J. Forster]

Certainly worth a try. If ventilation is an issue, copper window screen,
soldered alond the whole seam though.

-John

============

> Sounds like it would be an easy experiment to wrap some copper sheet
> around the motor frame and tack solder the ends. Might do the same mag
> field "shorting" that the copper accomplished for those transformers.
>
>
>  Wayne
>
>
>
> -----Original Message-----
> From: J. Forster <jfor at quikus.com>
> To: rbethman <rbethman at comcast.net>
> Cc: boatanchors <boatanchors at mailman.qth.net>
> Sent: Thu, Jan 2, 2014 12:45 pm
> Subject: Re: [Boatanchors] Need magnetic shield for shaded pole motor
>
> The layers of copper inside transformers are for electrostatic shielding
> between windings. Not magnetic. They are never connected from start to
> frinish, because that would be a shorted turn. They're entirely
> capacitive.
>
> Some transformers have a copper band wrapped around the outside of the
> core, with beginning soldered to the end of the turn. That copper layer is
> for mahnetic shielding, due to eddy currents.
>
> -John
>
> ==============
>
>
> > Industry uses multiple layers of copper in transformer construction
> for
> > magnetic shielding.
> >
> > It is "usually" enameled and grounded to the case later in the
> building
> > process.
> >
> > They don't consider the expense in the same way that the amateur
> radio
> > population does.
> >
> > Annealing of mu metal and steel is a normal part of the process.
> Other
> > applications are used in manufacture of brass cartridge cases. A bit
> OT.
> >
> > Bob - N0DGN
> >
> > On 1/2/2014 2:50 PM, J. Forster wrote:
> >> The problem with mu-metal is that machining (cutting & bending)
> destroys
> >> its magnetic shielding properties. There is another shielding
> material,
> >> called Netic-Conetic that is more forgiving.
> >>
> >> Copper is OK, provided it's several skin depths thick.
> >>
> >> I do agree that coffee cans are a bit on the thin side. If you
> can find
> >> a
> >> tin-plated-steel can of heavier guage, go for it. A source might
> be the
> >> larger 'family size' soup cans or the dumpster behind a
> resteraunt.
> >>
> >> The tin plating is mostly a rust preventative. A light coat of
> clear
> >> Krylon will do fine.
> >>
> >> -John
> >>
> >> ===============
> >>
> >>> Jim,
> >>>
> >>> Non-ferrous metals, copper etc., will do little to attenuate
> a magnetic
> >>> field. There is an alloy, know an mu-metal, that was designed
> just for
> >>> such applications, but it's expensive and hard to come by.
> Google same.
> >>> Start here:
> >>>
> http://www.pmlindia.com/hi-perm/Magnetic-Shield.htm?gclid=CJ3ghvWc4LsCFTNp7AodLUsAmA
> >>>
> >>> However, mu-metal only has a slight edge over soft iron or
> even steel.
> >>> The coffee can may be a little too thin. The wreckage of a
> LARGE
> >>> transformer may be the place to start.
> >>>
> >>> Al
> >>>
> >>> On 1/2/2014 2:22 PM, Charlie , W5COV wrote:
> >>>> I keep some handy copper sheets on hand all of the time
> now, comes in
> >>>> handy for various projects. This that I keep on hand, can
> be cut with
> >>>> scissors, and is relatively cheap, as am I <grin> .
> >>>>
> >>>> I picked it up from a from a place called Electronics
> Goldmine.
> >>>> http://www.goldmine-elec-products.com/
> >>>>
> >>>> Really handy to have around.
> >>>>
> >>>> Usual disclaimer no financial interest, just a satisfied
> customer.
> >>>>
> >>>> Charlie, W5COV
> >>>>
> >>>> On 1/2/2014 1:14 PM, rbethman wrote:
> >>>>> Use either the cut up coffee can as John suggests,
> they ARE becoming
> >>>>> another rarity.
> >>>>>
> >>>>> Now the coffee is coming in plastic containers. :^(
> >>>>>
> >>>>> Copper is still available as a roofing/flashing item
> in the Home
> >>>>> Improvement stores.
> >>>>>
> >>>>> I have procured some silver plated copper expanded
> mesh some years
> >>>>> back.
> >>>>>
> >>>>> It was offered on one of the mailman.qth.net lists.
> It may have been
> >>>>> this one or it may have been the glowbugs list.
> >>>>>
> >>>>> Bob - N0DGN
> >>>>>
> >>>>> On 1/2/2014 11:33 AM, J. Forster wrote:
> >>>>>> A cut up coffee can? Seriously.
> >>>>>>
> >>>>>> -John
> >>>>>>
> >>>>>> ============
> >>>>>>
> >>>>>>
> >>>>>>> Any ideas for an effective Gaussian shield
> for an open frame shaded
> >>>>>>> pole
> >>>>>>> motor or a source for very high permeability
> transformer core uncut
> >>>>>>> sheets.
> >>>>>>>
> >>>>>>> Thanks for any ideas--- Kindest regards Jim
> K9AXN
> >>>>>>>
> >>> --
> >>> Al Klase – N3FRQ
> >>> Jersey City, NJ
> >>> http://www.skywaves.ar88.net/
> >>>
> >
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