Rewinding method for small transformers. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies
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A simple method of mechanization is proposed, which allows actually rewinding the primary winding of a small-sized transformer in half an hour. For these purposes, you can use a small electric motor, for example, such as DPR or DPM.
A common malfunction of imported "Chinese" radio tape recorders is the combustion of the mains transformer. This is mainly due to poor-quality winding of the transformers themselves or due to the inattention of users (sometimes they accidentally switch the input voltage switch of the radio 127/220 V). Such a transformer, of course, requires replacement or rewinding.
Rewinding the transformer is complicated by the fact that the primary winding burns out, which in small-sized transformers contains 4500 or more turns of wire with a diameter of 0,06 ... 0,09 mm. Therefore, winding such a transformer manually is not so simple. As a rule, the transformers used in imported radio tape recorders are sectional and the windings in them are wound next to each other, and not one on top of the other. This allows you to replace the primary winding without touching the secondary.
In the transformer, first of all, it is checked whether there is a fuse built into the transformer in series with the winding, since it may turn out that there is no need to rewind the transformer. If there is no fuse, then the transformer plates are disassembled and the primary winding is cut off with a cutter, having previously marked on the plastic frame to what level the winding was wound. Having cut off the winding and cleaned with a file, the frame from the burrs and the remnants of the varnish that flooded the winding, fix the frame on the motor shaft. The easiest way to do this is to wrap electrical tape or adhesive tape around the motor shaft in such a way that the transformer frame fits snugly on the motor. As a rule, such a fastening is sufficient, since the transformer is wound with a thin wire.
Next, measure the diameter of the wire with which the transformer was wound. It is very important to choose a wire for winding just such a diameter, since with an increase in diameter of only one hundredth, it will not be possible to wind the transformer correctly and the required number of turns, most likely, will not fit in the small-sized transformer frame. Having picked up the desired wire, solder it to a piece of the mounting wire, which will serve as the output of the winding, insulate the place of soldering with varnished cloth and fix it in the frame with several initial turns. Before that, you need to check in which direction the frame rotates on the engine by applying a supply voltage to the latter.
It is desirable to supply voltage to the motor from a regulated source and not more than 5 ... 7 V, otherwise there is a danger of breaking the wound wire. It is desirable to bend the protruding end of the wire so that it does not dangle when the frame rotates, it also applies to the free terminals of the secondary winding if it is located on the same frame with the primary winding. Next, turn on the engine and, holding the wire, wind it around the frame.
There is no need to count the turns: the wire is wound up to the level to which the previous winding was wound. When the number of layers of wire in the frame reaches the mark made earlier, it is advisable to wind 300-500 turns on top of this (you can “by eye”). This will make the design more reliable, since transformers usually get quite hot due to the fact that they do not wind the required number of turns, apparently saving the wire.The output voltage will change slightly, so you can ignore this.
A wire is soldered to the upper terminal of the obtained primary winding and fixed with a thread. Then the plates are assembled and the transformer is ready.
Transformers rewound in this way, as a rule, work even better than "native" ones.
Author: I.A. Korotkov, Bucha village, Kyiv region
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