Calculate transformer secondary voltage from primary voltage, primary current, secondary current, or primary and secondary turns, and step-up/down type. Both models assume an ideal AC transformer and positive RMS winding values; losses, regulation and magnetizing current are excluded.
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Secondary Voltage Formula
The following formula is used to calculate the Secondary Voltage.
Formula source: College Physics 2e (OpenStax), Section 23.7 “Transformers”
- Where V2 is the Secondary Voltage (volts)
- V1 is the primary voltage (volts)
- I1 is the primary current (amps)
- I2 is the secondary current (amps)
For the ideal-transformer power-balance model, multiply primary RMS voltage by primary RMS current, then divide by secondary RMS current. The turns model uses V2/V1 = N2/N1. Equal voltage does not by itself establish galvanic isolation, and three-phase line values must not be mixed with winding values.
How to Calculate Secondary Voltage?
The following example problems outline how to calculate Secondary Voltage.
Example Problem #1
- First, determine the primary voltage (volts). In this example, the primary voltage (volts) is determined to be 300.
- Next, determine the primary current (amps). For this problem, the primary current (amps) is measured to be 2.
- Next, determine the secondary current (amps). In this case, the secondary current (amps) is found to be 3.
- Finally, calculate the Secondary Voltage using the formula above:
V2 = V1 * I1 / I2
Inserting the values from above and solving the equation yields:
V2 = 300 * 2 / 3 = 200 (volts)
Example Problem #2
Using the same method as above, determine the variables required by the equation. For this example problem, these are:
primary voltage (volts) = 500
primary current (amps) = 4
secondary current (amps) = 2
Entering these given values into the calculator or the formula above yields:
V2 = 500 * 4 / 2 = 1000 (volts)
