Calculate transformer voltage, current, and turns ratio using V₁/V₂ = N₁/N₂. Step-up, step-down, impedance matching. Includes efficiency and power loss.
The ideal transformer is a fundamental device in electrical engineering that transfers energy between circuits through electromagnetic induction while allowing voltage and current levels to be changed by the turns ratio. The core relationship V₁/V₂ = N₁/N₂ = I₂/I₁ governs this transformation, making transformers essential for power distribution, electronic power supplies, and impedance matching.
This calculator computes secondary voltage, primary current, power transfer, impedance ratio, and losses for any transformer configuration. It accounts for efficiency losses that reduce the idealized performance, making results useful for real-world applications. Whether the transformer steps voltage up (for transmission) or down (for distribution and end use), the same physics applies.
From the massive transformers on utility poles stepping down 13.8 kV to 240/120V household voltage, to the tiny transformers in phone chargers converting 120V to 5V, this calculator serves engineers, electricians, students, and electronics hobbyists who need to design or analyze transformer circuits. The reference tables provide context for common applications and their typical specifications.
Transformer calculations involve reciprocal relationships between voltage and current, squared relationships for impedance, and efficiency corrections that are easy to mix up. This calculator handles all three transformer equations simultaneously, computes the power triangle, and shows impedance transformation — saving time and preventing errors that could lead to overloaded or undersized components.
Ideal Transformer Equations: V₁/V₂ = N₁/N₂ (voltage ratio) I₁/I₂ = N₂/N₁ (current ratio, inverse) Z₁/Z₂ = (N₁/N₂)² (impedance ratio) With efficiency: I₁ = (I₂ × N₂/N₁) / η P_loss = P_primary − P_secondary Where: N₁, N₂ = number of turns V₁, V₂ = voltages I₁, I₂ = currents η = efficiency (decimal)
Result: V₂ = 24V, I₁ = 1.02A, turns ratio = 10:1
With a 10:1 turns ratio, 240V primary produces 24V secondary. At 10A secondary load, ideal primary current would be 1A, but with 98% efficiency it is 1.02A. Secondary power is 240W, with about 4.9W lost as heat.
A transformer consists of two or more coils (windings) wound around a shared magnetic core. AC current in the primary winding creates a time-varying magnetic flux in the core, which induces a voltage in the secondary winding via Faraday's law. The voltage ratio equals the turns ratio, while the current ratio is its inverse — conserving power (in the ideal case).
The electric power grid relies entirely on transformers. Generators produce electricity at 11-25 kV. Step-up transformers raise this to 138-765 kV for long-distance transmission (reducing I²R losses). Substation step-down transformers reduce voltage to 13.8-69 kV for distribution. Final pole-mounted or pad-mounted transformers step down to 120/240V for homes and 480V for commercial buildings.
In audio engineering, output transformers match the low impedance of tube amplifier outputs (a few hundred ohms) to speakers (4-16Ω). In radio frequency design, baluns (balanced-to-unbalanced transformers) match antenna impedance to transmission line impedance. The impedance transforms as the square of the turns ratio, making transformer selection critical for maximum power transfer.
The turns ratio is N₁/N₂, the ratio of primary to secondary winding turns. It determines the voltage transformation ratio: V₂ = V₁ × (N₂/N₁). A 10:1 ratio means the secondary voltage is one-tenth of the primary.
No. Transformers work by electromagnetic induction, which requires a changing magnetic field. DC produces a constant field, so no voltage is induced in the secondary. This is why AC power was adopted for transmission.
Impedance matching uses a transformer to make a load appear to have a different impedance. Since impedance transforms as (N₁/N₂)², a 10:1 transformer makes a 4Ω speaker look like 400Ω to the amplifier, maximizing power transfer.
Core losses (hysteresis and eddy currents in the magnetic core) and copper losses (I²R heating in the windings). Modern laminated silicon-steel cores and optimized winding designs achieve 98-99% efficiency in large power transformers.
A step-up transformer has more secondary turns than primary, increasing voltage while decreasing current. A step-down transformer has fewer secondary turns, decreasing voltage while increasing current. Power is conserved (minus losses) in both cases.
Transformer losses depend on current (copper losses) and voltage (core losses), regardless of the load's power factor. A 100 kVA transformer can supply 100 kW at unity power factor or 80 kW at 0.8 PF — the heating is the same in both cases.