[Boatanchors] Need magnetic shield for shaded pole motor
hwhall at compuserve.com
hwhall at compuserve.com
Fri Jan 3 14:29:36 EST 2014
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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