I have two transformers, one is 120VA, the other 7VA. I want to encase them in aluminium covers I've made, which give about 4mm clearance around each of the transformers. My plan was to cover the cases in MuMetal shielding.
Is it advisable to drill ventilation holes in the base and top? Will this affect the shielding properties of the MuMetal?
The transformers will not be highly loaded, I'm thinking this will be like an encapsulated transformer. Hopefully the experts can give me advice on this one. I'd rather not drill them unless it's advisable to do so.
Many thanks for any advice.
Is it advisable to drill ventilation holes in the base and top? Will this affect the shielding properties of the MuMetal?
The transformers will not be highly loaded, I'm thinking this will be like an encapsulated transformer. Hopefully the experts can give me advice on this one. I'd rather not drill them unless it's advisable to do so.
Many thanks for any advice.
Any working of mu metal can reduce its shielding properties, which in any case is only good for fairly low fields. Put mu metal around the things which need to be protected from the field, not the source of the field. For a power transformer a belly band is probably a better way to reduce any external magnetic field.
What is a mu metal? That grey alloy plate? It has been used for ages to screen transformers, as well as line-level amplifiers. In transformers by transformer's manufacturer, and around sensitive amp (not around transformer) by device manufacturer. Rarely I have seen mu-metal used to "screen" transformer.
In RF devices, I only found aluminum block (no mu-metal), may be mixed with silver. Once I found gold for shielding
Mu metal is a specific alloy containing nickel, iron, copper and chromium. It is specifically designed for low level screening, for instance tape heads and microphone transformers and is very effective. It is little use for power transformers since it easily saturates at higher flux densities and becomes inefective. It also requires heat treatment after any bending or machining which makes it difficult for the DIYer. Since it is a greyish alloy it is not easy to identify visually but it is a fair bet that any screening can round a power transformer is not mu metal.
RF screening is an entirely different problem and skin effect makes the use of copper, aluminium and even silver and gold effective.
RF screening is an entirely different problem and skin effect makes the use of copper, aluminium and even silver and gold effective.
From most of the RG integrated models to the $20k monaural power amps.
http://www.symphonic-line.de/0501_symphonic_line_preise_vollverstaerker.html
Skin depth of Mu metal at 50-60Hz makes foil useless, thickest i have is 0.1mm
A can in Mu metal with 0.5-1.0mm wall thickness for a 300VA size does ~$150, cheaper options.
http://www.symphonic-line.de/0501_symphonic_line_preise_vollverstaerker.html
Skin depth of Mu metal at 50-60Hz makes foil useless, thickest i have is 0.1mm
A can in Mu metal with 0.5-1.0mm wall thickness for a 300VA size does ~$150, cheaper options.
Last edited:
That's very interesting, $150 is quite reasonable. I couldn't find a list of sizes on his website. Is this something you contact him directly for?
The aluminium is 5mm, I have Ultraperm 80 sheets of Mumetal. I'll put them on anyway as it's a nicer finish than the alu alone.
I also notice the on the photo you posted the only openings are at the base (regarding ventilation).
The aluminium is 5mm, I have Ultraperm 80 sheets of Mumetal. I'll put them on anyway as it's a nicer finish than the alu alone.
I also notice the on the photo you posted the only openings are at the base (regarding ventilation).
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.