Transformer turns ratio calculator
A transformer trades voltage for current at constant power, and squares that ratio when it reflects impedance.
V
V
A
%
ohm
Turns ratio
19.166 67
- Primary current
- 0.2746 A
- Secondary power
- 60.00
- Primary power
- 63.16
- Losses
- 3.16
- Load impedance seen at the primary
- 2938.889 ohm
- Transformer VA rating needed
- 60.0 VA
Show the working
- Primary voltage = 230
- Secondary voltage = 12
- Secondary current = 5
- Efficiency = 95
- Secondary load impedance = 8
- Turns ratio = 230 / 12 = 19.1667
- Secondary power = 12 * 5 = 60
- Primary power = 60 / (95/100) = 63.1579
- Primary current = 63.1579 / 230 = 0.2746
- Load impedance seen at the primary = 8 * 19.1667^2 = 2938.89
- Losses = 63.1579 - 60 = 3.157 89
- Transformer VA rating needed = 60 = 60
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Vp/Vs = Np/Ns
- Ip/Is = Ns/Np for an ideal transformer
- reflected impedance = load impedance x (turns ratio)^2
Impedance transforms as the square of the turns ratio, which is the whole basis of impedance matching with a transformer.