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	Subject - Single Phase Transformers David Hyatt All right this ones for fun. You have a single phase transformer, 120volt primary, 24volt secondary with a secondary load of 500va. The efficiency is 100%. What is the primary current? What is the primary current if it was 96% efficient? JimmyDee 500 va 120 = 4.16666 amps @ 100% effecient At 96% effecient = 4 amps David Hyatt Jim, just noting that at 100% efficiecy output va = input va. And when efficiecy goes down, input goes up, and output stays the same. 500va output = 500va input, thus at 100%, 500/120= 4.16a. So now at 96% eff. input= output/eff: 500/.96= 520.83333input va. 520.83333/120=4.34 primary current. Show your work please.Ha Ha Just wait I will be back on 3phase transformers tonight. JimmyDee Actually if you had that transformer loaded to 500va on the secondary, you are correct on the amperage but it wouldn't last long because the primary would burn up because it would be overloaded. Jim David Hyatt Jim, I don't understand why it would burn up, why is it overloaded. This question came from my exam calculations workbook. JimmyDee 96% eff. input= output/eff: 500/.96= 520.83333input va. 520.8 va on a winding that is rated for 500 va = smoke. Jim Ryan_J Another "just for fun". What is the turns ratio of the aforementioned transformer? David Hyatt Turns ratio 5 to 1.