How to determine the number of turns of transformer windings

When the type or not of transformer data is unknown, the number of turns of each winding can be determined with a multimeter.

Using an ohmmeter, determine the location of the terminals of all the transformer windings. If there are gaps between the coil and the magnetic circuit, an additional winding is wound over the windings with a thin wire. The more turns the winding has, the more accurate the measurement results will be.

If there is no space on the transformer coil for an additional winding, then instead of an additional winding, you can use part of the outer winding. To do this, carefully open the outer insulation layer of the coil to gain access to the last layer of the winding, made, as usual, turn to turn. A number of turns are counted from the end of this winding in the “naked” layer. Carefully clean the enamel of the last counted turn.

When measuring, one probe of the voltmeter is connected to the end of the winding, the needle is clamped to the other probe. An ohmmeter measures the resistance of all windings, a winding with high resistance is primary.

In the case when there are still windings with high resistance, one of the windings with low resistance is taken as the primary one and a low alternating voltage is applied to it, for example, 6 V from any power transformer.

They apply voltage to the primary winding and measure the voltage across all windings. If used as the primary winding with low resistance, then determine the primary winding of the transformer. Having applied the mains voltage to it, they once again measure the voltage across all the windings.

Using the data of voltage measurements on each winding, the number of turns is determined by the formula: Wn = UnWdop / Udop, where Wn - the number of turns of any winding, Un - voltage on this winding, Udop - voltage on the additional winding, Wdop - number of turns of the additional winding.

V.F. Yakovlev

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