How to determine the data of an unknown transformer
To determine the data of an unknown transformer, you need to wind an auxiliary winding over the windings of the transformer, consisting of several turns of insulated copper wire with a diameter of 0.12 — 0.4 mm. Then, by measuring the resistances of the windings with an ohmmeter, it is necessary to determine the winding with the highest resistance and, considering it as the primary, apply to it the alternating current voltage (about 50 - 220 V). A voltmeter connected to the auxiliary coil circuit will show the voltage U2. Number of turns x in the winding connected to the network can then be determined by the formula X = (U1 / U2) NS Y, where Y — the number of turns of the auxiliary winding.
Transformation factor between these windings is equal to the ratio Y : x... In the same way, you can determine the number of turns and the transformation coefficients of other windings.The accuracy of calculations using this method depends on the accuracy of the voltmeter readings and the number of turns of the auxiliary coil: the greater the number of turns, the higher the accuracy.