| murat |
Can we shield a non-metal box with aluminum foil for amplifier enclosure? - maybe folded 4-5 times? Anyone tried?
Murat |
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| SY |
| Works fine (ask John Curl). The major issue is making a good, reliable electrical connection to it. |
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| murat |
If multi-folded, heavy-duty foil look pretty strong. I am thinking squuezing it between two washers of bolt-nut assembly. I get pretty good contact resistance even when I touch it with multimeter leads. Thanks,
Murat |
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| Panelhead |
| quote: | Originally posted by murat
Can we shield a non-metal box with aluminum foil for amplifier enclosure? - maybe folded 4-5 times? Anyone tried?
Murat |
The foil may work. But www.lessemf.com has some really nice mu-metal that works much better. A single thickness will shield more than a bunch or aluminum foil.
The stuff is fairly inexpensive. A 16" wide sheet is 18.95 per linear foot. It is surprisingly heavy and stiff for the thickness.
George |
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| SY |
Keep an eye on that contact resistance- it's likely to go up significantly over time. You've got a mechanical contact between two metals with very different work functions and reduction potentials, one of which has a high creep... That's the problem with aluminum foil for anything other than a lab lash-up.
Copper or brass foil, now those are solderable and now you're talkin' good shielding. |
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| Cortez |
Sorry for off-ing: what is the best metal material to use for shielding,
to protect electonical ccts and components against disturbs from "outside" ? |
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| jacco vermeulen |
| quote: | Originally posted by Panelhead
It is surprisingly heavy and stiff for the thickness. |
Not surprising, MU metal is mainly Nickel.
Specific weight of Nickel is 10% higher than that of steel.
Nickel is one of the main additives for hardened and high tensile steels.
As a kid i was often allowed to "help out" in my dads plant.
Some parts for production tools had to be made of nickel, for hardness and durability.
Machining the stuff was pretty difficult, an eight year old was very good at pressing the red button when one the tool sides was precision grinded. |
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| phase_accurate |
Aluminium is also solderable, if you know how to do it !!
Regards
Charles |
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| murat |
Charles, no, I don't know how to solder aluminum. Are you planning to tell us?
Cortez, I don't know.
Murat |
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| Cortez |
| Aluminum to solder ? Hmm... How ? :) |
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| phase_accurate |
There are two prerequisites:
1). The aluminium item isn't too large, i.e. it can't sink too much of heat. A heatsink would therefore be a bad object.
2.) It must be a little sturdy, so it would be a little difficult to do with a thin foil. It might work better when already glued to a sturdy surface.
The procedure:
Apply a drop of oil to the place where you want to solder your wire to. This works of course best on horizontal planes looking upside.
The oil is used as a temporary barrier against our atmosphere.
Without interrupting the oil-film one now scratches the surface of the aluminium by the use of a sharp knife in order to get rid of the oxyde layer.
Now you can apply the solder with a powerful iron. This has to be done quickly because the solder has to stick before all the oil is evapourated.
One has to do it several times in order to get some practice.
Good luck and fun !
Charles |
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| IanAS |
Am I wrong in thinking that aluminium does not sheild from transformer fields?
And Mu metal loses it's special properties when bent, hammered or drilled?
From my own experience, it takes at least 5 layers of GOSS to stop the field from a 500VA toroid.
Micheal Percy Audio is offering a multilayer metal for shielding. I've not used it and can't comment on it efficacy. Sorry can't link to it as last time I looked he doesn't have an on-line cataolgue. |
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| Mr Evil |
Whether you use aluminium foil or mumetal depends on what you want to shield. Aluminium (or copper, which is better) is best for keeping out electric fields, but will do nothing for magnetic fields. Mumetal is great at shielding against magnetic fields, but will do little to keep out an electric field. Generally I would say that magnetic fields are not a big problem (containing the external field from an E-I core transformer is an exception - a good reason to use toroids!).
This is all due to the physical properties of the shield. High electrical conductivity to block electric fields, high magnetic permeability to block magnetic fields. It's also worth noting that whereas it is possible to completely shield against an electric field, magnetic fields will always get through a little because they induce an electric current in the shield, which will itself re-radiate a magnetic field inside the shield.
I have used aluminium foil to shield things before. It can be very effective, even with only a single layer. Equipment thus treated usually ends up looking like some sort of mutant baked potato.
Oh, and that tip for soldering to aluminium could be useful. I've tried soldering to it before and it's a pain in the ****.:mad: |
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| rcavictim |
| I was given a tour once by the owner oif a famous capacitor manufacturer plant. I was intruiged by the process they used to 'solder' a conductive strap to the wound foil ends of a rolled pulse capacitor. They used a large industrial soldering iron like an American Beauty, 100-150 watt with a big aluminum tip. The solder was ordinary 50-50 lead-tin (or 60-40?) with NO FLUX. |
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| jacco vermeulen |
| quote: | Originally posted by IanAS
Mu metal loses it's special properties when bent, hammered or drilled? |
MU-foil can be cut to size, folded to shape.
Bending results in local plastic deformation, the bent line looses its properties and acts as discontinuous.
MU-foil is very thin, but folding it is difficult.
Besides as foil MU is produced in other shapes, such as round cups.
20 years ago i bought cinch plugs with MU outer shielding, should have acquired more than the 8 i have.
A box i glued MU-foil on was tested for magnetic shielding by a former collegue of Aalt-Jouk VandenHull at the electronics faculty, it performs rather well. |
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| jacco vermeulen |
| quote: | Originally posted by Mr Evil
a good reason to use toroids |
A good reason to shield toroids with MU foil ! |
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| ingvar ahlberg |
One efficient way to make a good electrical connection to aluminium foil is by attaching a piece of cu tape, conductive adhesive, and soldering wire to cu tape. This method works industrially and is used in test equipment for high tension lines
>30kV. If alu foil is laminated with plastic, solder wire to coppertape before attaching to alu foil. |
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| markp |
| quote: | Originally posted by IanAS
And Mu metal loses it's special properties when bent, hammered or drilled?
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Anything that changes the crystaline structure of the Mu metal damages its properties |
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| zBuff |
Would using a spray can of something like CRC "Zinc It" work for shielding? the final dried layer 'suppose' to be 95% pure zinc.
would have to be a pretty thick coat though I guess, and soldering is going to be problematic. |
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| thomas997 |
| quote: | Originally posted by zBuff
Would using a spray can of something like CRC "Zinc It" work for shielding? the final dried layer 'suppose' to be 95% pure zinc.
would have to be a pretty thick coat though I guess, and soldering is going to be problematic. |
I have a cheap preamp thats like that. There is some sort of copper spray on the inside, connections are made with gold plated springs pushing up against it. |
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