Transformer Efficiency

Compute efficiency from input/output power, primary/secondary V×I, or loss method. Includes show-work and share links.

How to Use

  1. Select a method (Power, V×I, or Losses).
  2. Enter the required values and choose units.
  3. Enable “Auto-scale” to display W/kW cleanly.
  4. Open “Show Work” to see steps in base units.
Transformer Lab View
Visual feedback: efficiency gauge + loss bar.
η
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Pin
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Pout
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Loss
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Status: —
Transformer Primary Secondary Efficiency —% η = Pout / Pin Loss fraction Visuals scale with computed efficiency and loss fraction. This tool is an estimator; real-world efficiency depends on load, temperature, and waveform.
Inputs & Settings
Choose a method. Enter values; results update instantly.
Auto will prefer the most complete consistent set.
Electrical input power to the transformer.
Useful output power delivered to the load.
RMS voltage for AC. Use consistent waveform assumptions.
RMS current for AC (or DC for special cases).
Load-side RMS voltage.
Load-side RMS current.
Also called iron loss; often near-constant with voltage/frequency.
Winding loss (I²R), increases with load current.
If PF is used: P ≈ V×I×PF (RMS). PF must be 0–1.
Show Work (step-by-step)
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Work is shown in base units (W, V, A) for clarity. For V×I, RMS assumptions apply.

Reference

  • Efficiency: η = Pout / Pin
  • Percent: η% = 100 × (Pout / Pin)
  • Loss: Ploss = Pin − Pout
  • Loss method: Pin = Pout + (Pcore + Pcopper)
  • V×I estimate: P ≈ Vrms × Irms (or × PF if provided)

Note: This tool does not model regulation, magnetizing current, harmonics, temperature rise, or frequency-dependent core behavior.

FAQ

Why can efficiency change with load?

Core loss is often closer to constant, while copper loss rises with current. At light load, fixed losses dominate; near rated load, copper loss grows.

Is V×I always real power?

No. For AC, V×I is apparent power (VA). Real power depends on power factor (PF). If you know PF, enable it to estimate real power.

Can efficiency exceed 100%?

Not physically. If you see >100%, inputs are inconsistent (units, PF assumptions, or measurement error).

Tool Info

Last updated:

Updates may include unit support, UI improvements, and edge-case handling.