Transformer Calculator

Transformer Formulas

Basic Transformer Equation

Vp / Vs = Np / Ns = Is / Ip

Where:

• Vp = Primary Voltage
• Vs = Secondary Voltage
• Np = Primary Turns
• Ns = Secondary Turns
• Ip = Primary Current
• Is = Secondary Current

Power Formula

Power (VA) = Vp × Ip = Vs × Is (ideal, no losses)

Turns Ratio

Turns Ratio = Np / Ns = Vp / Vs

Step-Up Transformer

Increases voltage, decreases current. Example: 120V to 480V

Vs = Vp × (Ns / Np) where Ns > Np

Step-Down Transformer

Decreases voltage, increases current. Example: 480V to 120V

Vs = Vp × (Ns / Np) where Ns < Np

Common Transformer Ratios

• 480V to 120V: 4:1 ratio
• 240V to 120V: 2:1 ratio
• 208V to 120V: 1.73:1 ratio
• 120V to 24V: 5:1 ratio
• 277V to 120V: 2.3:1 ratio

Transformer Efficiency

Real transformers have losses due to:

• Copper losses (I²R heating)
• Core losses (eddy currents, hysteresis)
• Leakage flux

Typical efficiency: 95-98% for power transformers