An ideal transformer is defined entirely by its turns ratio: V₁/V₂ = N₁/N₂. Because power in
equals power out for an ideal device, current runs the other way — I₂/I₁ = N₁/N₂ — so a
step-down winding that halves the voltage doubles the current. Drag either turns slider here and every other
number updates instantly, because they're all derived from that one ratio.
230V into a 1000:100 turns transformer (a 10:1 ratio) gives 23V out. A 100W load at 23V draws 4.35A on the secondary and 0.43A on the primary — checked against ampere-turns balance, 1000 × 0.43A matches 100 × 4.35A exactly.
Two loss mechanisms eat into it: core (iron) losses from magnetising the core, which are present constantly whenever the transformer is energised regardless of load, and copper losses from winding resistance, which scale with the square of the load current. Distribution transformers typically run 97–99% efficient at full load; large power transformers can exceed 99.5%.
Efficiency is maximised exactly where copper loss equals core loss — since core loss is constant and copper loss grows with current squared, that crossover typically happens around 40–70% of rated load for distribution transformers, which is also why they're deliberately sized a little larger than their average expected load.
A real mains transformer might use hundreds or thousands of turns per winding — this tool draws the turns ratio at a legible scale (the presets pick small whole numbers with the same ratio) so the physics stays identical while the diagram stays readable.
Only for the ideal case. Real transformers also have leakage inductance, magnetising current, and winding resistance that this tool's core equations don't model — turns ratio gets you the voltage and current relationship exactly right, which is most of what matters for a first-pass calculation.