When creating electronic structures, transformers with unknown parameters are sometimes used. In this case, it is necessary to determine the transformer windings, their input and output voltages, the number of turns.
Most often, when creating homemade electronic structures, step-up and step-down transformers are used. Their design is quite simple - a coil with windings is placed on an electrical steel core. By changing the number of turns in the secondary winding, you can get a voltage that is different from that supplied to the primary winding.
The primary winding is the winding to which the voltage is applied. Secondary - the winding to which the load is connected. The primary winding is wound first, on top of it, through the insulation layer, the secondary. Knowing this principle, you should carefully inspect the transformer and determine the terminal connected to the outer winding wire. If there are only two windings and four terminals on the transformer, then the found terminal will belong to the secondary winding.
You can find the second terminal of the secondary winding using a multimeter (tester). Connect one probe of the device to the external terminal, with the second, alternately touch the other three terminals. In one case, the device should show the presence of a circuit, this will be the second output of the secondary winding. The two remaining pins will belong to the primary.
Having identified the primary and secondary windings, measure their resistance. If the transformer is a step-up, the resistance of the secondary winding will be greater than that of the primary, this is due to the increased number of turns. For a step-down transformer, the secondary resistance will be less.
Some transformers have more than four terminals. This means that additional intermediate voltages are removed from the secondary winding. The primary (mains) winding in this case will be a winding with two leads. For a step-down transformer, the diameter of the wire can help determine the secondary winding - it is thicker than on the primary. This is due to the fact that as the voltage decreases, the current strength increases.
To determine the number of turns of the windings, wind an additional one with a known number of turns over the secondary winding - for example, there may be 50. Then apply a small voltage (9-12 V) to the primary winding. Measure the voltage on the secondary and auxiliary winding. The number of turns is calculated according to the formula: n = Un × Wadd / Uadd. Here n is the number of turns of the transformer winding, Un is the voltage acting on this winding, Wadd is the number of turns in the additional winding, and Uadd is the voltage across it.