[Boatanchors] Need magnetic shield for shaded pole motor

[J. Forster]

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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