Transformer Efficiency & Turns Ratio Calculator
Calculate transformer turns ratio, voltage transformation, current transformation, and efficiency for any AC transformer.
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Transformer Guide
What should I know about Transformer Basics?
A transformer is two coils (windings) sharing a magnetic core. Alternating current in the primary creates a changing magnetic field, which induces an EMF in the secondary. Only works with AC — DC produces no changing field, so no induction. Turns ratio: N_p / N_s. Determines voltage ratio. Voltage ratio: V_p / V_s = N_p / N_s. Current ratio (ideal): I_p / I_s = N_s / N_p (inverse of voltage ratio). Step-up: secondary has more turns than primary. V_s > V_p. Used in: power transmission, from generators at the power station through to the national grid, stepping voltage up for efficient long-distance transmission and back down for safe local use.
Why High-Voltage Transmission?
Power transmitted: P = V × I. For given power, doubling V halves I. Resistive loss in cables: P_loss = I²R. Halving I quarters losses. Why pylons carry 132-400 kV: minimises transmission losses across long distances. Substations step down progressively: 400 kV → 132 kV → 33 kV → 11 kV → 400 V (domestic 3-phase) → 230 V (single phase domestic). Each step-down via large transformer. Power station typically produces 11-25 kV initially. Step up to 400 kV for grid distribution. Step down at consumer substations in stages, typically to 11kV for local distribution and then to 230V for the final connection into homes.
What do I need to know about Real Transformer Losses?
Ideal transformer: 100% efficient. Real transformers: 95-99% for power transformers. 85-95% for small domestic transformers. Losses come from: copper losses (I²R in windings) — depend on load. Iron losses (eddy currents in core + hysteresis) — constant regardless of load. Laminated cores: reduce eddy currents (insulating layers between thin steel sheets). Silicon steel: reduces hysteresis losses. Toroidal cores (donut-shaped): minimal magnetic leakage, higher efficiency. Larger transformers are more efficient overall than small ones, since core and winding losses don't scale up in proportion to power handled, giving big grid transformers efficiencies well above 99%.
What should I know about Applications?
Domestic: every plug-in 'wall wart' adapter contains a transformer (or modern switch-mode equivalent). Steps 230V to 5-12V for electronics. Computer PSUs: combine transformer with rectification and regulation. EV charging: charging stations contain transformers stepping down grid voltage. Welding: massive step-down transformers (240V to ~30V at hundreds of amps). Audio: output transformers in valve amplifiers match speaker impedance. Isolation transformers: 1:1 ratio. Used for safety isolation rather than voltage change, breaking a direct electrical connection between two circuits — common in bathroom shaver sockets and some medical equipment.