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I want to make a transformer that steps down mains AC voltage. My researched showed that the best kind of material for core would be laminated iron sheets. Unfortunatelly, these are very hard to buy. Looks like you can only get ferrite cores online.

So is there some different material, that is easily accessible by regular hobbyists, that can be used for making transformer cores? It should be able to buy it in local stores.

I'm aware that I could salvage core from old electrical appliance like TV or microwave, but that is cost inefficient if you don't already have that appliance. So I'm looking for some better alternative.

Edit - I'm located in Eastern Europe, if that helps.

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    \$\begingroup\$ You used to be able to get a transformer kit, with the laminations, a pre-wound primary, and an empty section on the bobbin for your own secondary... Possibly follow the breadcrumbs here, no guarantees they still lead anywhere. vintage-radio.net/forum/showthread.php?t=66411 \$\endgroup\$
    – user16324
    Commented Sep 17, 2017 at 14:51
  • \$\begingroup\$ Last time I wanted a custom mains transformer, I bought a complete toroidal transformer of the appropriate VA rating, with as low a secondary voltage as possible (fewest secondary turns), unwound the secondary carefully, and was left with a mains primary-wound toroid, through which I then threaded my custom secondaries. Just a thought. \$\endgroup\$
    – Neil_UK
    Commented Sep 17, 2017 at 15:04
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    \$\begingroup\$ Why do you want to build your own transformer? Why aren't the commercial offerings good enough? \$\endgroup\$ Commented Sep 17, 2017 at 15:13
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    \$\begingroup\$ Beware: common iron sheets are not as good as you think. The core losses would be relevant, even if you laminated the core and insulated each lamination. The fact is that iron is a decent conductor hence eddy currents will cause large amount of heat losses. You would need special iron-based material, such as Fe-Si alloys, which have higher resistivity and thus greatly reduce eddy currents. \$\endgroup\$ Commented Sep 17, 2017 at 15:22
  • \$\begingroup\$ @BrianDrummond I bought a 50VA one of those at Maplin in London a "few" years ago. \$\endgroup\$ Commented Sep 17, 2017 at 15:42

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You don't divulge your location so it is hard to gauge what might be present in your local stores, but you can buy toroidal transformer kits with pre-wound primaries (117VAC) and just add the secondary winding. Here is a supplier.

The volts per turn varies with VA as shown in this table:

enter image description here

You can get cores from old products you might find at the curb on garbage day (or at recycling of electronics days) but most modern products use switching power supplies- microwave ovens being an exception, but even there many newer models are of the "inverter" type.

Hopefully you can do better than this homemade welding transformer:

enter image description here

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  • \$\begingroup\$ I'm located in Eastern Europe, if that helps. \$\endgroup\$
    – elecbegin
    Commented Sep 17, 2017 at 18:39
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For the transformer core, you want to use steel laminations with 3% silicon for the magnetic properties. Steel sheets have a resistance to magnetic reversal, and the silicon reduces that.

However, you can make your own, custom, core that actually works quite well. You can buy powdered iron. Make the mold out of wax, mix the powdered iron with an epoxy resin that is about the same consistency as fiberglass resin. Make certain the particles are not clumped together and you have a good concentration of iron. Add the drops of hardener, mix well, and pour it into the mold. Next day, remove the wax. I have a 3KVA isolation transformer that I wound last year, 1:1 turns ratio for 120 VAC that has been doing just fine. To mix the powder into the resin, I used a hand-held blender. As you add powder, the resin becomes almost like a paste, but thins out slightly after you add the hardener.

For the windings, there is no substitute for copper.

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  • \$\begingroup\$ How would you account for the 3% silicon with this approach? What form of silicon is used? Elemental silicon powder? Or some silicon compound? Or even more likely, is it an steel-silicon alloy? \$\endgroup\$
    – Jeffrey
    Commented Sep 4, 2022 at 22:20

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