Transformer Calculator

About Transformer Calculator

Transformer: Vp/Vs = Np/Ns. Step-down reduces voltage (Ns < Np). Ideal transformers conserve power: VpIp = VsIs.

How to use this calculator

1. Enter the primary voltage and secondary voltage, or the turns on one side if you know them.
2. Use the ratio \(\frac{V_p}{V_s} = \frac{N_p}{N_s}\) to find the missing value.
3. Check whether the transformer is stepping voltage up or down.
4. Read the result and compare it with your circuit requirements.

The formula explained

The formula \(\frac{V_p}{V_s} = \frac{N_p}{N_s}\) shows that the voltage ratio equals the turns ratio. It tells you how to find an unknown voltage or coil turns when the other values are known.

• \(V_p\) = primary voltage, the input voltage
• \(V_s\) = secondary voltage, the output voltage
• \(N_p\) = number of turns on the primary coil
• \(N_s\) = number of turns on the secondary coil

Step by step method

1. Write the ratio \(\frac{V_p}{V_s} = \frac{N_p}{N_s}\).
2. Substitute the known values and cross multiply.
3. Solve for the missing voltage or turns.

Worked example

Problem. A transformer has \(V_p = 120\) volts and \(N_p = 600\) turns. If the secondary coil has \(N_s = 150\) turns, what is \(V_s\)?

1. Start with \(\frac{V_p}{V_s} = \frac{N_p}{N_s}\). Substitute the values to get \(\frac{120}{V_s} = \frac{600}{150}\).
2. Simplify \(\frac{600}{150} = 4\), so \(\frac{120}{V_s} = 4\).
3. Solve for \(V_s\): \(V_s = \frac{120}{4} = 30\).

Tips and common mistakes

• Make sure the primary and secondary values are not swapped, because that changes the answer.
• This formula gives the ideal transformer ratio, so it does not include real-world losses.

Frequently asked questions