Transformer Calculator

Calculate transformer turns ratio, voltage/current transformations, power conservation, and efficiency. Perfect for electrical engineering, power distribution, and electronics design.

**Transformer Turns Ratio:** Vs / Vp = Ns / Np Where: • Vs = Secondary voltage (V) • Vp = Primary voltage (V) • Ns = Number of secondary turns • Np = Number of primary turns **Current Transformation:** Is / Ip = Np / Ns = Vp / Vs Where: • Is = Secondary current (A) • Ip = Primary current (A) **Power Conservation (Ideal):** Vp × Ip = Vs × Is Pin = Pout **Efficiency:** η = Pout / Pin × 100% η = (Vs × Is) / (Vp × Ip) × 100% **Key Relationships:** • Step-up: Ns > Np → Vs > Vp, Is < Ip • Step-down: Ns < Np → Vs < Vp, Is > Ip • Isolation: Ns = Np → Vs = Vp, Is = Ip **Turns per Volt:** TPV = Np / Vp = Ns / Vs (constant for given core)
**Example 1 (Step-Down Transformer):** Primary: 240 V, 100 turns, 2 A Secondary: 500 turns • Turns ratio = 500/100 = 5:1 (step-up) • Wait, this is actually step-UP! Let's fix: Secondary = 50 turns • Turns ratio = 50/100 = 0.5 • Vs = 240 × 0.5 = 120 V (step-down) • Is = 2 × (100/50) = 4 A • Power: 240×2 = 480 W = 120×4 ✓ **Example 2 (Phone Charger):** Primary: 120 V, 1000 turns Secondary: 5 V, ? turns • Ratio = 5/120 = 0.0417 • Ns = 1000 × 0.0417 = 41.7 ≈ 42 turns • If Ip = 0.1 A, then Is = 0.1 × (1000/42) = 2.38 A **Example 3 (Step-Up for Power Line):** Primary: 240 V, 100 turns Secondary: 24,000 V (24 kV), ? turns • Ratio = 24,000/240 = 100 • Ns = 100 × 100 = 10,000 turns • If Ip = 100 A, then Is = 100 × (100/10,000) = 1 A • Power: 240×100 = 24,000 W = 24,000×1 ✓ **Example 4 (Microwave Transformer):** Primary: 120 V, 500 turns, 10 A Secondary: 2000 V, ? turns • Ratio = 2000/120 = 16.67 • Ns = 500 × 16.67 = 8333 turns • Is = 10 × (500/8333) = 0.6 A • Power: 1200 W (magnetron power) **Example 5 (Efficiency Calculation):** Input: 120 V × 5 A = 600 W Output: 12 V × 48 A = 576 W • Efficiency = 576/600 × 100% = 96% • Power loss = 600 - 576 = 24 W • Loss = 4% (Very Good rating) **Example 6 (Isolation Transformer 1:1):** Primary: 120 V, 1000 turns Secondary: 120 V, 1000 turns • Ratio = 1:1 (isolation only) • Voltage: same (120 V) • Current: same • Purpose: electrical isolation, safety **Example 7 (Multi-tap Transformer):** Primary: 240 V, 1000 turns Secondary taps: • Full winding (500 turns): 120 V • Half winding (250 turns): 60 V • Quarter (125 turns): 30 V **Example 8 (Welding Transformer):** Primary: 240 V, 2000 turns, 20 A Secondary: 40 V, ? turns • Ratio = 40/240 = 0.167 • Ns = 2000 × 0.167 = 333 turns • Is = 20 × (2000/333) = 120 A (high current!) • Power: 4800 W **Example 9 (Real vs Ideal):** Ideal: Pin = 1000 W → Pout = 1000 W Real (95% efficient): Pin = 1000 W → Pout = 950 W • 50 W lost as heat in windings and core

What is a transformer?

A transformer is a device that transfers electrical energy between two or more circuits through electromagnetic induction. It can step voltage up or down while maintaining power (minus losses). Transformers only work with AC (alternating current), not DC.

What is the turns ratio formula?

The turns ratio relates voltages and currents: Vs/Vp = Ns/Np = Ip/Is, where Vp and Vs are primary and secondary voltages, Np and Ns are number of turns, and Ip and Is are currents. The turns ratio determines voltage transformation.

How does a transformer step up or step down voltage?

Step-up transformer: Ns > Np, so Vs > Vp (more secondary turns = higher voltage). Step-down transformer: Ns < Np, so Vs < Vp (fewer secondary turns = lower voltage). Current changes inversely: higher voltage = lower current.

Is power conserved in a transformer?

In an ideal transformer, power is conserved: Pin = Pout, or Vp×Ip = Vs×Is. Real transformers have 95-99% efficiency due to resistive losses, core losses (hysteresis and eddy currents), and flux leakage. Power rating must not be exceeded.

What happens to current in a transformer?

Current transforms inversely to voltage: Is/Ip = Np/Ns = Vp/Vs. If voltage doubles (step-up), current halves. If voltage halves (step-down), current doubles. This maintains power conservation: high voltage × low current = low voltage × high current.

Why do transformers only work with AC?

Transformers require changing magnetic flux to induce voltage (Faraday's law). AC constantly changes, creating changing flux. DC is constant, producing no flux change after initial switch-on, so no continuous voltage induction. Frequency typically 50-60 Hz for power.

What is transformer efficiency?

Efficiency η = Pout/Pin × 100%. Losses include: copper losses (I²R in windings), core losses (hysteresis and eddy currents), and stray losses. Power transformers: 95-99% efficient. Small transformers: 80-95%. Efficiency improves at higher power levels.

Can I connect a transformer backwards?

Yes! Transformers are reversible. A 120V-to-12V step-down transformer can work as a 12V-to-120V step-up transformer if you swap primary and secondary. However, check current ratings - the "new primary" winding must handle the input current.

What is the difference between step-up and step-down transformers?

Step-up: increases voltage (Ns > Np), decreases current. Used for power transmission (reduce I²R losses). Step-down: decreases voltage (Ns < Np), increases current. Used for distribution (safe voltage levels). Structurally, they're the same - just different turns ratios.

What voltage do I get with a 2:1 turns ratio?

A 2:1 ratio (Np:Ns = 2:1) is a step-down transformer. If Vp = 240V, then Vs = Vp × (Ns/Np) = 240 × (1/2) = 120V. Current doubles: if Ip = 1A, then Is = Ip × (Np/Ns) = 1 × 2 = 2A.

How do I calculate required number of turns?

Turns per volt (TPV) method: TPV = Np/Vp (constant for a core). Then: Ns = Vs × TPV. Example: 100 turns for 10V primary gives TPV = 10 turns/volt. For 50V secondary: Ns = 50 × 10 = 500 turns.

What are typical transformer applications?

Power distribution (grid: 100kV to 240V), phone chargers (120V to 5V), microwave ovens (120V to 2kV), doorbells (120V to 16V), welding (step-down for high current), X-ray machines (step-up for high voltage), isolation (medical equipment).

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