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I have an application for 2 no. 50VA toroidal transformers that will be used as a power supply running off 240V mains. This will be a linear supply in the traditional sense.

But. I am considering mounting the transformers externally to any physical enclosure. It will kinda be glued onto the side of a metal support lattice. It will then be surrounded by conductive wire mesh of various types. Imagine a toroidal transformer sat snugly in the middle of a bird's nest. The nest will be coiled aluminium and steel wires of random lengths and thicknesses. Some might be the thickness /texture of wire wool. Some like coat hangers, maybe some 6mm diameter steel and a few 25mm * 25mm * 1.6mm aluminium angles. Some may be 50mm long and some 500mm long. This can all be explained by the term "Functional Art."

My concern is secondary inductance, heating, fire and possibly death. How can this be made to work satisfactorily? I'm fully prepared to accept that this might not be possible within a domestic budget, but I'm not looking for comments stating that this is a bad idea. I'm looking for a good engineering effort to enable this, but will abandon in extremis.

My sense of it is that this is very possible as long as none of the nest metal work forms a full loop though the middle of the torroid. So loops around the perimeter might be okay? I know about not shorting the top and bottom of the fixing bolts.

A side question is: if the torroids cannot be mounted within the wire nest, how far away might they have to be?

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  • \$\begingroup\$ Wire wool can be a definite fire hazard, pass 3-4 amps through it and it has enough resistance to glow red or ignite easily. Otherwise, Olin's advice is spot on. \$\endgroup\$ Sep 3 '16 at 21:57
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    \$\begingroup\$ Good catch! Wire wool's an old bush craft trick for fire lighting. Wire wool's out. \$\endgroup\$
    – Paul Uszak
    Sep 3 '16 at 22:04
  • \$\begingroup\$ @Paul, Two years have passed from the time that you've made the question. The technical question was answered, but the curiosity remains. Did you make it? Could you post a photo? \$\endgroup\$
    – mguima
    Oct 1 '18 at 13:09
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What you want to do is OK as long as there is no conducting loop thru the center of the torus and back around the outside. A simple way to guarantee this is to put something insulating in the middle of the torus so that nothing conducting can make a complete loop that includes going thru the middle. A piece of cardboard, plexiglass, phenolic, circuit board without traces on it, etc, would do it.

Toroidal transformers are pretty good at containing the magnetic fields, but some will still be present outside the torus. Something conducting immediately outside the torus will pick up the stray magnetic field and will have some eddy currents thru it. Those should be nowhere near strong enough to cause excessive voltages or heating. They might be strong enough to upset delicate analog circuitry though. Keep such things a full major radius or so from the outside of the torus.

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