How this calculation works
Use an ideal AC turns ratio for RMS voltage and equal apparent-power magnitudes for the corresponding load currents. Keep VA separate from real power and do not infer a hardware rating.
Vs/Vp = Ns/Np; |Ip| = S/Vp; |Is| = S/VsA worked example
500 primary turns and 1,000 secondary turns give a ratio of 2. With 230 V RMS on the primary, ideal secondary voltage is 460 V RMS. At an entered 100 VA load, primary current is about 0.434783 A and secondary current about 0.217391 A.
Good to know
Ideal AC magnitudes only: no loss, magnetizing current, saturation, winding resistance, frequency/flux, insulation, phase group or rating model. Steady DC operation is not implied. Zero load VA is not a prediction of real no-load consumption.
Reference: Reference: model definitions and scope (opens in a new tab) ↗
A turns ratio changes voltage and current in opposite directions
The default 1,000 secondary turns over 500 primary turns gives a ratio of two. At 230 V RMS primary voltage, the ideal secondary is 460 V RMS. With an entered 100 VA load, the secondary current is about 0.217391 A and the primary current about 0.434783 A.
The higher ideal output voltage is accompanied by lower current for the same apparent power. It is not a doubling of energy. The model omits losses and magnetizing current, so it cannot predict a real transformer’s heating, regulation or no-load consumption.
The electrical power calculator uses a DC relationship. The ideal transformer here uses AC RMS magnitudes and load apparent power in VA.
VA is not automatically real watts
The entered load is apparent power, the product of RMS voltage and current magnitudes. Real power also depends on the load’s power factor. Treating the VA input as watts without that additional condition would add an assumption the calculator has not made.
The table varies primary voltage while holding the same apparent-power load and turn counts. Current therefore changes inversely with voltage. That is a set of fixed-VA scenarios, not a prediction for one fixed resistor whose power would change with voltage.
Ideal AC ratios do not specify a physical transformer design
Positive whole turn counts define a ratio but do not determine a core, frequency range, flux density, insulation or winding rating. This AC model does not imply that steady DC produces the same transformed output. Zero entered load gives zero load current in the idealization; real magnetizing current is not calculated.
The electrical power calculator uses a separate DC voltage-times-current relationship. The battery nominal energy and runtime calculator uses another constant-voltage energy budget. Neither supplies the omitted magnetic, AC or thermal details needed to turn this turns-ratio exercise into an equipment selection.
A few questions, answered
Does a step-up ratio increase power?
Not in the ideal model. Voltage increases while the corresponding current decreases for the same apparent power.
Is the load input in watts?
It is VA. Real watts require the appropriate load power factor.
Does zero load mean a real transformer draws nothing?
No. The model omits magnetizing current and no-load losses.
Can the AC relationship be applied directly to steady DC?
No. The supported model is an ideal AC transformer, without a magnetic-design calculation.