Transformer Calculator
Calculate transformer turns ratio, voltage, and current from primary and secondary specifications.
Formula
Vp/Vs = Np/Ns = Is/Ip
Where Vp and Vs are primary and secondary voltages, Np and Ns are primary and secondary turns, and Ip and Is are primary and secondary currents. For an ideal transformer, power in equals power out: Vp x Ip = Vs x Is.
Worked Examples
Example 1: Residential Step-Down Transformer
Problem: A transformer has 500 primary turns at 240V and needs to output 120V with a 1000W load at 95% efficiency. Calculate secondary turns, currents, and losses.
Solution: Turns Ratio = 240 / 120 = 2:1\nSecondary Turns = 500 / 2 = 250 turns\nSecondary Current = 1000 / 120 = 8.333A\nIdeal Primary Current = 1000 / 240 = 4.167A\nInput Power = 1000 / 0.95 = 1052.63W\nActual Primary Current = 1052.63 / 240 = 4.386A\nPower Loss = 1052.63 - 1000 = 52.63W
Result: Turns: 2:1 (500:250) | Primary: 4.386A | Secondary: 8.333A | Loss: 52.63W
Example 2: Industrial Step-Up Transformer
Problem: A step-up transformer converts 120V to 480V with 200 primary turns and a 5000W load at 97% efficiency.
Solution: Turns Ratio = 120 / 480 = 0.25:1 (step-up)\nSecondary Turns = 200 / 0.25 = 800 turns\nSecondary Current = 5000 / 480 = 10.417A\nInput Power = 5000 / 0.97 = 5154.64W\nActual Primary Current = 5154.64 / 120 = 42.955A\nPower Loss = 5154.64 - 5000 = 154.64W\nImpedance Ratio = 0.25^2 = 0.0625
Result: Turns: 0.25:1 (200:800) | Primary: 42.96A | Secondary: 10.42A | Loss: 154.64W
Frequently Asked Questions
How does a transformer work and what is the turns ratio?
A transformer works on the principle of electromagnetic induction, transferring electrical energy between two or more windings through a shared magnetic core. The turns ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding, expressed as Np divided by Ns. This ratio directly determines the voltage transformation relationship, where Vp divided by Vs equals Np divided by Ns. A transformer with 1000 primary turns and 500 secondary turns has a turns ratio of 2 to 1, meaning it steps down the voltage by half. The turns ratio is the most fundamental parameter in transformer design and determines whether the transformer steps voltage up or down.
How do you calculate transformer efficiency and power losses?
Transformer efficiency is calculated as the ratio of output power to input power, expressed as a percentage using the formula Efficiency equals output power divided by input power times 100. Power losses in transformers come from two main sources: copper losses and core losses. Copper losses, also called I-squared-R losses, occur due to the resistance of the winding conductors and increase with the square of the current. Core losses include hysteresis losses from the continuous magnetization and demagnetization of the core material and eddy current losses from circulating currents induced in the core. Modern power transformers typically achieve efficiencies of 95 to 99 percent. Distribution transformers are usually rated at 97 to 99 percent efficiency at full load.
What is impedance ratio and why is it important in transformer design?
The impedance ratio of a transformer equals the square of the turns ratio, expressed as the quantity Np divided by Ns, all squared. This relationship is crucial for impedance matching in electronic circuits, particularly in audio equipment and RF applications. For example, a transformer with a 10 to 1 turns ratio has an impedance ratio of 100 to 1, meaning a 100 ohm load on the secondary appears as a 10,000 ohm impedance on the primary side. Maximum power transfer occurs when the source impedance matches the load impedance. Audio output transformers use this principle to match the high impedance of vacuum tube amplifiers to the low impedance of speakers, ensuring efficient power delivery.
How do you size a transformer for a specific application?
Sizing a transformer requires determining the VA (volt-ampere) rating, which is calculated by multiplying the secondary voltage by the maximum secondary current. For resistive loads, VA equals watts, but for inductive or capacitive loads you must account for the power factor. A motor drawing 10 amps at 120 volts with a power factor of 0.8 requires 1200 VA but only consumes 960 watts. Always add a safety margin of 20 to 25 percent above the calculated VA rating to prevent overheating and ensure reliable operation. Consider ambient temperature conditions since transformers derate at higher temperatures. For applications with significant inrush current like motors, size the transformer to handle the starting current, which can be 5 to 8 times the running current.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
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