Magnetic starter transformer
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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When designing a home-made power supply, winding a network transformer causes a certain difficulty, especially in the absence of a winding machine. You can purchase a ready-made transformer, but it does not always provide the required parameters of the power supply. The most time-consuming in the manufacture of the primary winding.
I propose a variant of the design of the transformer, in which there is already a primary winding. A standard magnetic starter of suitable dimensions is required, for example, PME111, etc. Such starters are widely used in industrial electrical equipment. They can be with faulty contacts, a split case, but always with a working retracting coil.
The starter must be disassembled, the coil and both halves of the magnetic circuit removed. There is enough space on the coil to accommodate the secondary winding until the magnetic circuit window is filled. In this case, the main winding is used as the primary winding and is connected to the electrical network. The data for calculating the number of turns of the secondary winding are available on the starter coil itself. It shows the rated mains voltage, mains frequency, number of turns, brand and wire diameter. For example, U=220 V 50 Hz W=4100 vit PEV-2 O 0,14 mm . Based on these data, the number of turns of the secondary winding is calculated depending on the required voltage at its output.
The calculation is made according to the formula WII \u10d WIUII / UI where WII is the number of turns of the secondary winding; WI is the number of turns of the primary winding; UI - voltage on the primary winding; UII - voltage on the secondary winding. The calculated number of turns of the secondary winding must be increased by 15 - XNUMX%. The wire diameter is taken depending on the load current and the conditions for filling the magnetic circuit window. After winding the secondary winding, it must be insulated with any insulating material.
On one of the halves of the magnetic circuit there are short-circuited copper turns. There are two of them in the PME111 magnetic starter I mentioned. These coils need to be removed, you can just open it. This reduces the magnetizing current consumed from the network (no-load current) and the heating of the transformer decreases.
After checking the parameters of the wound transformer, the ends of the magnetic circuit must be glued together. To do this, the ends of both halves of the magnetic circuit must be cleaned of dirt, oil and degreased with a solvent (acetone, etc.). Then grease the ends with epoxy glue, insert both halves into the coil and lightly clamp in a vise. After the adhesive has hardened (24 hours at normal temperature), the transformer is ready. The transformer made in the described way works silently.
Author: E. Kolesnikov, Gavrilsk village, Voronezh region
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