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Old 10-02-2009, 21:06   #1
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How far or what covering/shielding?

How many miles should equipment like my Isolation Transformer and Charger/Inverter be away from my compasses and other electronic equipment?
Is their any covering/shielding that could be installed to decrease the magnetic effect of these devices?
Any guidance would be great.

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Old 10-02-2009, 22:05   #2
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Strength of magnetic fields drops dramatically with distance. Without pulling out an old engineering manual I think the field strength drops as a square of the distance. So a few feet away should be sufficient for most euipment from the compass. You can always switch them on and off and check the compass on different headings to check. Make sure you check wiring that runs near the compass.

What other electronics are you concerned with interference from the transformer?
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Old 11-02-2009, 02:59   #3
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Transformer

It would only be the amount of iron in the core that would/could effect a compass & the field produced by the AC voltage/current would not be a problem. Actually the presence of the AC field would destroy stray magnetic fields!! (first principal of a degauser)

The DC current involved with the inverter/charger would have to be kept away by a distance & tested to see if deviation is produced when in use.

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Old 11-02-2009, 05:22   #4
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Your Isolation Transformer and Charger/Inverter should be at least 3 feet from your compass - further being better.

Steel and Iron objects, as well as electric circuits close to the compass may cause magnetic Deviation.

As skipmac indicates magnetic fields follow an inverse-square law near the magnet, but follow an inverse cubed law further away; so that the field becomes exponentially weaker as separation increases. As Bill indicates, it’s the magnetic core of the Transformer that causes magnetic Deviation (just like your engine block), not the effects of rapidly reversing Alternating Current.

You cannot practically (see posts 6 & 7) shield against static magnetic fields, such as those caused by a magnetic mass (above).

RF shielding is possible to mitigate the electro-magnetic (radiation) effects generated by Direct Current wiring. The easiest method is to simply twist the (2) DC wires, effectively cancelling the generated fields.
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Old 11-02-2009, 22:40   #5
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Good stuff.

Thanks Guys.

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Old 12-02-2009, 01:28   #6
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Quote:
Originally Posted by GordMay View Post
<snip>
You cannot shield against static magnetic fields, such as those caused by a magnetic mass (above).

<snip>
Mu Metal is quite good for screening against static magnetic fields.
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Old 12-02-2009, 04:02   #7
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Wotname is correct; I should have said no practical way to magnetically shield.
There is no known material that blocks magnetic fields without itself being attracted to the magnetic force. Magnetic fields can only be redirected, not created or removed.
Magnetic Shielding can be accomplished by placing a high permeability material (such as Mumetal®) between the field source and the sensitive components affected. Such material must be conductive to prevent passage of electric fields and highly permeable to prevent passage of magnetic fields. Shielding materials commonly used have permeabilities from 300 to over 500,000 depending on flux density. Closed shapes (without seams or openings), such as cylinders with caps, boxes with covers, etc, are the most efficient for magnetic shielding.

Unfortunately, Mumetal is extremely expensive, and challenging to work with.

Magnetic shielding using superconducting magnets is also being researched as a means of shielding spacecraft from cosmic radiation.

See the FAQs:
Frequently Asked Magnetic Shielding Questions
and:
Solve magnetic interference problems with magnetic shields.
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Old 13-02-2009, 03:12   #8
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Gord is correct; I should have said mu metal is theoretically good for screening against static magnetisc fields but is bloody difficult to work with and achieve a positive result.
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