I am not changing voltage, just splitting the phase. Would this work?

240V single phase to 240V split phase

21 windings on the primary 21 Windings on the secondary Center tap the 11th for N


  • L-N 240


  • L1-N-L2
  • L1-N 120
  • L2-N 120
  • L1-L2 240

5000-watt max input

Will this work with any odd number of windings 3 or more? Do there need to be hundreds of windings or can I simplify the transformer by using large gauge wire to work with fewer windings? Center tap the center winding for the new N?

  • 1
    \$\begingroup\$ What kind of magnetic core? How the core was calculated? How did you calculate the number of windings per volt? If you can't answer at any of these question, don't play with mains, please - it can be very risky and can kill you. \$\endgroup\$ Jan 21, 2020 at 2:52
  • \$\begingroup\$ by my reckoning you'll need about 25 turns for each 120V winding assuming you start with a 5kVA core. \$\endgroup\$ Jan 21, 2020 at 5:15
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    \$\begingroup\$ 5kW input means you should concern yourself with good design specs before you waste your money and time.. No load loss, Primary Inductance, Full load loss. max temp rise., (80'C max hot spot) thermal resistance with 500W loss. cooling and insulation design for 6kV, Short Circuit current. Lamination loss W/kG , Core shape. etc How many kg and what lamination size do you know ?? \$\endgroup\$ Jan 21, 2020 at 5:36

1 Answer 1


Just for your consideration, here's a cut away of a transformer that is approximately rated for 240 volts on the primary: -

enter image description here

I estimate it has maybe 800 or more turns on the primary and this would be consistent in achieving a primary magnetization inductance of several henries.

Would this work? 21 windings on the primary

No, it will catch fire or trip the breakers immediately. However, if you told me that your AC frequency were in fact 100 kHz instead of 50/60 Hz then 21 turns sounds reasonable.


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