Ideal Transformer Calculator
Find the secondary voltage and current of an ideal transformer from its turns ratio and primary values.
How it works
Vₛ ÷ Vₚ = Nₛ ÷ Nₚ · Iₛ ÷ Iₚ = Nₚ ÷ Nₛ · Vₚ·Iₚ = Vₛ·Iₛ
In an ideal transformer the voltage ratio equals the turns ratio, and because power is conserved the current ratio is its inverse — a step-down transformer that halves voltage doubles the available current. Real transformers lose a little to resistance and core heating, so treat the output as an ideal upper bound. Transformers only work on alternating current, since a changing flux is what induces the secondary voltage.
Worked example
A 1000:100 transformer (ratio 0.1) fed 230 V outputs 230 × 0.1 = 23 V. With 0.5 A in the primary, the secondary carries 0.5 ÷ 0.1 = 5 A, and power stays at 230 × 0.5 = 115 W.
Sources: Transformer — Wikipedia
Frequently asked questions
How does a transformer change voltage?
The secondary-to-primary voltage ratio equals the turns ratio Nₛ/Nₚ. More turns on the secondary steps voltage up; fewer turns step it down. The changing magnetic flux from the AC primary induces the secondary voltage.
Does a transformer create power?
No. An ideal transformer conserves power, so raising voltage lowers current in the same proportion (and vice versa). Real units are slightly lossy but never output more power than they take in.
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This calculator is for educational purposes. Double-check important results before acting on them.