Transformer Turns Ratio Calculator Formula

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

Use the Transformer Turns Ratio Calculator

Formulas Used

Turns Ratio (Np/Ns)

turns_ratio = v_primary / v_secondary

Secondary Current

secondary_current = v_primary * primary_current_a / v_secondary

Apparent Power

power_va = v_primary * primary_current_a

Variables

VariableDescriptionDefault
v_primaryPrimary Voltage(V)120
v_secondarySecondary Voltage(V)12
primary_current_aPrimary Current(A)0.5

How It Works

Transformer Turns Ratio

Formulas

Np/Ns = Vp / Vs

Is = Ip x Np/Ns (ideal transformer)

Power = Vp x Ip = Vs x Is

An ideal transformer conserves power. Real transformers have 90-98% efficiency due to copper and core losses.

Worked Example

120 V primary to 12 V secondary, 0.5 A primary current.

v_primary = 120v_secondary = 12primary_current_a = 0.5
  1. 01Turns ratio = 120 / 12 = 10:1
  2. 02Secondary current = 0.5 x 10 = 5 A
  3. 03Power = 120 x 0.5 = 60 VA

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