Transformer Calculator Formula

Understand the math behind the transformer calculator. Each variable explained with a worked example.

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Formulas Used

Turns Ratio (N2/N1)

turns_ratio = n2 / n1

Secondary Voltage

v2 = v1 * n2 / n1

Secondary Current

i2 = i1 * n1 / n2

Variables

VariableDescriptionDefault
v1Primary Voltage(V)120
n1Primary Turns500
n2Secondary Turns50
i1Primary Current(A)1

How It Works

Transformer

A transformer transfers electrical energy between circuits via magnetic coupling, changing voltage and current levels.

Formulas

V2 / V1 = N2 / N1 (voltage ratio equals turns ratio)

I2 / I1 = N1 / N2 (current ratio is inverse of turns ratio)

Power is conserved in an ideal transformer: P1 = P2.

Worked Example

A step-down transformer: 120 V input, 500 primary turns, 50 secondary turns, 1 A primary current.

v1 = 120n1 = 500n2 = 50i1 = 1
  1. 01Turns ratio = N2/N1 = 50/500 = 0.1
  2. 02V2 = V1 * N2/N1 = 120 * 0.1 = 12 V
  3. 03I2 = I1 * N1/N2 = 1 * 500/50 = 10 A
  4. 04Power check: 120*1 = 12*10 = 120 W

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