Transformer Calculator — Voltage, Current & Turns Ratio
Turns Ratio
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Secondary Turns
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Secondary Current
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Primary Current
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Understanding Transformer Turns Ratio and Voltage
A transformer converts AC voltage from one level to another through electromagnetic induction between two coils wound around a shared magnetic core. This calculator determines the output voltage, turns ratio, and current based on the primary voltage, primary turns, and secondary turns. It applies the fundamental transformer equation: V_primary / V_secondary = N_primary / N_secondary, where N represents the number of wire turns in each coil.
The turns ratio directly controls the voltage transformation. A step-down transformer with a 10:1 turns ratio converts 120V AC to 12V AC. A step-up transformer with a 1:5 ratio converts 120V to 600V. The power relationship P = V * I means that when voltage steps down, current steps up proportionally (assuming ideal efficiency), and vice versa. Real transformers have losses from copper resistance in the windings and iron core losses from hysteresis and eddy currents, typically achieving 95-98% efficiency in well-designed units.
Transformers are fundamental components in power distribution, electronics, and industrial equipment. Power utilities use massive step-up transformers at generating stations to transmit electricity at high voltage over long distances, then step-down transformers at substations and on utility poles to deliver usable voltage to homes and businesses. In electronics, small transformers in power supplies convert wall outlet voltage to the low voltages needed by circuit boards. This calculator is useful for engineers designing power supplies, electricians selecting replacement transformers, and students learning electromagnetic principles.
Frequently Asked Questions
What is a turns ratio?
The turns ratio is the ratio of primary winding turns to secondary winding turns. It determines the voltage transformation. A 10:1 turns ratio with 120V primary gives 12V secondary.
How does transformer current relate to voltage?
Power in equals power out (minus losses). If voltage goes down, current goes up proportionally. A transformer stepping 120V to 12V increases current by 10x (minus efficiency losses).
What about transformer efficiency?
Real transformers have 90-99% efficiency depending on size and design. Small transformers may be 85-95% efficient. This calculator shows ideal values; actual current may be 5-15% higher.