A transformer transfers electrical energy through changing magnetic flux linking its windings. In the ideal two-winding model, the secondary-to-primary voltage ratio equals the secondary-to-primary turns ratio. Use the calculator to compare step-up and step-down ratios and the period of an AC cycle. The illustration shows separate windings on a common core; it does not determine the voltage, power or insulation rating of a real transformer.
Alternating Current Transformer Interactive Calculator
Vary primary turns, secondary turns, and AC frequency to see the ideal transformer turns ratio, voltage ratio, and animated magnetic flux.
Equation Used
The worked example uses the ideal transformer turns-ratio equation. With primary turns Np and secondary turns Ns, the secondary-to-primary voltage ratio is Vs/Vp = Ns/Np. For Np = 6 and Ns = 3, the transformer is a 2:1 step-down, so Vs/Vp = 0.5.
- Ideal transformer with negligible winding loss and flux leakage.
- Voltage ratio equals turns ratio for AC excitation.
- DC or static flux is not modeled because the worked example uses AC.
Changing flux links the windings
The applied primary voltage is associated with changing magnetic flux. Flux linking the secondary winding induces a voltage there. More linked turns produce a larger induced voltage for the same rate of flux change, giving the ideal turns-ratio relation.
The illustration shows a laminated magnetic core and two electrically separate windings. Laminations reduce eddy currents in a conductive core; other transformer designs use other core materials and constructions. A static magnetic field does not produce a continuous induced secondary voltage. Switching circuits can drive transformers from a DC supply by creating a time-varying waveform, which is different from applying steady DC directly.
Parts and effects
- Primary winding: receives the input excitation.
- Secondary winding: has induced voltage determined by linked flux and turn count.
- Core: provides the illustrated magnetic path.
- Insulation: separates conductors and structures in the actual device.
Real transformers have winding resistance, leakage flux, magnetizing current and core losses. Their voltage under load and temperature rise need more information than turns alone. No amount of turns-ratio arithmetic establishes an insulation or safe-touch rating.
Voltage conversion and isolation
Transformers are used in power distribution, control supplies, instrumentation and electronic converters. Line-frequency and high-frequency designs use the same induction principle but differ in magnetic materials, winding construction and operating conditions.
A transformer by itself does not rectify AC to DC and does not change the fundamental supply frequency. Rectifiers, switches and control circuits perform other functions in an electronic power supply. It is therefore incomplete to describe a charging cabinet or traction converter only by its transformer ratio.
For a real selection, use the required winding connections, voltage, frequency, VA rating, insulation system, installation conditions and load characteristics. The calculator supplies a ratio and period comparison rather than equipment selection.
Turns ratio and AC period
For the ideal two-winding model, Vs/Vp = Ns/Np. The reciprocal card is Np/Ns. Voltage Change = 100(Ns/Np − 1) percent, so a ratio of 0.5 means a 50% reduction and a ratio of 2 means a 100% increase.
At frequency f in hertz, AC Period = 1000/f milliseconds. Frequency does not appear in the ideal voltage-ratio equation. It does affect real magnetic design: for a sinusoidal waveform, induced voltage depends on frequency, turns and peak linked flux. The calculator does not evaluate core area, flux density or saturation.
For an ideal loaded transformer, the load-current ratio is inverse to the voltage ratio when magnetizing current and losses are neglected. That relation conserves power; it does not create a current or VA rating. Neither primary voltage nor load current is an input here.
Equal turn counts give a 1:1 ratio and zero voltage change. Choosing very small turn counts in the illustration is not a winding recipe for a mains transformer. Use the manufacturer’s ratings rather than assuming any displayed ratio is usable at any voltage or frequency.
Worked example: step-down and period
Enter 6 primary turns, 3 secondary turns and 60 Hz. Vs/Vp is 3/6 = 0.5; Np/Ns is 2. Voltage Change is −50%, and AC Period is 1000/60 = 16.67 ms.
Changing frequency to 50 Hz makes the period 20 ms while leaving both ratios and the voltage-change percentage unchanged. This describes the ideal calculation, not permission to connect a 60 Hz device to a 50 Hz supply.
Swapping the counts to 3 primary and 6 secondary gives Vs/Vp = 2, Np/Ns = 0.5 and a +100% voltage change. If an independent ideal example assumed 10 V input, its corresponding output would be 20 V. The turn counts still do not specify an actual transformer’s power or safe operating voltage.
Two windings, autotransformers and converters
| Arrangement | Electrical relationship | Important distinction |
|---|---|---|
| Separate-winding transformer | Windings couple magnetically without a shared conductive winding. | Required isolation performance depends on insulation design and rating. |
| Autotransformer | Input and output share part of a winding. | It does not provide galvanic isolation between those circuits. |
| Switch-mode converter | Switching electronics control energy transfer. | Some topologies include an isolating transformer; others do not. |
Efficiency, size, cost and lifetime depend on the particular design and loading. The ideal ratio model does not predict any of them.
Transformer calculation questions
The ideal ratio is Ns/Np. Frequency changes the AC period here, but real transformers also have magnetic and thermal limits that this model does not calculate.
No. An ordinary transformer changes voltage and current relationships, not the fundamental frequency. Frequency conversion needs additional equipment.
No. It is the percentage change relative to primary voltage. A value of−50% means the ideal secondary voltage is half the primary voltage.
The model assumes changing excitation. Steady DC does not sustain the alternating-flux process and may cause damaging current in a transformer intended for AC. Switched converters use time-varying drive rather than steady DC across an ordinary AC winding.
No. The ideal current ratio follows from power balance, but actual current and VA ratings require conductor, core, insulation, cooling and operating information.
No. Lower frequency at unchanged voltage can increase flux demand. Any frequency or voltage change must follow the exact manufacturer’s rating or written application guidance; a generic V/f calculation alone is not approval.
No. They omit load, impedance, supply conditions and faults. Do not treat an unexpected voltage as harmless phantom voltage or use this page as an energized-equipment test procedure.
No. The diagram shows electrical separation, not a safety rating. Actual insulation, grounding, connections and operating voltage determine the installation requirements.
References and further reading
Hammond Power Solutions: transformer introduction explains induction and turns ratios. Schneider Electric: transformers and supply frequency explains why an ordinary transformer does not convert frequency. Manufacturer application guidance, including frequency-rating guidance for specified Schneider products, is product-specific.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
