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I need a high power transformer with 240VAC primary at 10-16A and secondary of 6VAC 350-400A. I calculated that I would need a transformer core with cross sectional area of about 45cm2 to able to use about 1:1 windings per voltage.

My question is, how well will 0.5mm thick 1020 steel with 10-50micron zinc plating compete as tranformer core? I have two choices: take apart a bunch of microwave transformers or make one myself, and getting silicon steel sheets is impossible at any sensible price for me.

For getting 45cm2 CSA im planning on making a transformer EI type with core size 95x50mm, as using 100 pcs stack of 0.5mm plates.

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  • \$\begingroup\$ Is 6VAC 350-400A a continuous output or intermittent? If intermittent, then what's the duration and duty cycle? \$\endgroup\$
    – Nick Alexeev
    Commented Jul 5, 2013 at 19:08
  • \$\begingroup\$ I wouldn't do this if I were you. Those are dangerous levels. \$\endgroup\$
    – Brian Carlton
    Commented Jul 5, 2013 at 19:10
  • \$\begingroup\$ @BrianCarlton A person, who has diligence to seek a sanity check on transformer core material, is likely to survive a contact with 6VAC @ 60Hz. To avoid setting a building on fire is possible too. \$\endgroup\$
    – Nick Alexeev
    Commented Jul 5, 2013 at 20:22
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    \$\begingroup\$ I hate to say this, but: If you have to ask that question here, you should not be building a 400A transformer. \$\endgroup\$
    – shieldfoss
    Commented Jul 5, 2013 at 22:06
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    \$\begingroup\$ OC voltages in arc welders tend to be much higher - 20V and upwards. Sometimes it's a higher impedance 50-90V supply or RF generator to start the arc, then (say) 100-250A@20V under load to keep it going. 6V@400A sounds like a rather small spot welder, in which case duty cycle could be quite low. \$\endgroup\$
    – user16324
    Commented Jul 6, 2013 at 9:57

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If you can re-use a transformer core, do so. Dismantle and re-assemble a 2.4kw transformer if you can find one at that sort of power rating - it may be a mains isolation transformer - you may only have to rewind the secondary - or find a commercial rewinder. Or parallel a few smaller transformers.

The Si steel laminations pack together densely because they are formed with due regard for flatness, and the Si steel has relatively low loss (magnetisation) and relatively high saturation flux density. In all three of these factors you will lose out using off-the-shelf commercial sheet steel - unless you have specialist punch equipment, in which case you may be able to achieve the required flatness. (Otherwise expect it to buzz loudly and get warmer than a commercial core).

Spot welder, or heater supply for a retrocomputing project?

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