Winding transformers with your own hands is a task that any radio amateur sooner or later faces. If you don’t make a new one from scratch, then you’ll probably have to redo the old transformer radically. The point is not difficult, but long, monotonous and requires constant attention.
Winding scheme of the welding transformer.
Nevertheless, this task is quite feasible even for an inexperienced radio amateur: he will hardly be able to manufacture a toroidal transformer, but it will be possible to make a device of a more traditional type for sure.
Transformer winding tools
First of all, you should think about how to facilitate the work itself with the help of various devices. In the factory production of transformers, they are made, of course, with the help of special machines, and not manually.
It hardly makes sense for an amateur to think about a machine tool, but simple devices to facilitate the work will surely justify themselves.
The simplest option is two pillars attached to a wooden board and a metal rod between them, curved in the shape of a handle on one side. Outwardly, something like a spit. The rod will be threaded through the holes in the racks, usually not more than 1 cm thick. The axis of the "skewer" must be passed through the frame of the future transformer (we do not stop at its production, since its type and features depend on the intended function of the device). Usually, for this purpose, a wooden block is used with a hole for the axle and in size suitable for the frame.
Scheme of the machine for winding transformers.
With a hand drill, the task is simplified. The drill is securely fastened parallel to the table (you can simply hold it in a vice) so that its handle can rotate freely. A metal bar is inserted into the drill chuck with a block mounted on it, on which the transformer frame is fixed. Ideally, the rod should be threaded, then the block can be easily fixed by simply holding it with nuts on both sides. In some cases, it is possible to completely do without the pads, clamping the frame either by the nuts themselves, or by wooden plates or textolite plates.
You can use as a mechanism for winding a telephone inductor, a machine for textile spool, a device for rewinding film and other similar mechanisms. The key point is “soft”, without jerking, the course of the process.
In addition, you will need a device for unwinding (especially if you use an old transformer as a source of wire). Its progress should also be uniform, in order not to complicate the process of winding up a new transformer, and not damage the insulation of the wire. Usually the unwinding device is made by analogy with the winding device, but the handle for rotation is optional.
An additional device for counting the number of turns may also be useful. You can get by with a verbal account when every turn is counted (or a pair of turns), and every hundred is marked on paper. If a gear machine is used, the transmission ratio should not be forgotten.
However, you can use any device. Suitable water meter, electric meter, speedometer for a bicycle. The counter is connected to the machine for winding using a flexible roller (rubber tube with sufficiently thick walls) or gears.Back to table of contents
Insulation winding layers
The scheme of the primary and secondary windings.
Often it is required to insert insulating spacers between the layers of the wire. Usually they are made of paper, the best cable or condenser. Pads must be thick, level, free from holes and openings.
Between the adjacent transformer windings, insulation is much more serious. Lakotkan is usually used, on both sides of which paper is placed ("sandwich"). A layer of paper is also needed to level the surface before winding the next winding. In the absence of varnished cloth, the same paper can be used in several layers (at least 3) instead.
Strips of paper for insulating spacers are made wider than the winding, its edges should extend 2-4 mm beyond the turns of the winding. Along the edges, the excess is bent up, thus protecting the outermost turns.Back to table of contents
The winding itself is as follows.
The coil with the wire is fixed in the unwinding device, and the transformer frame - in the winding. This must be done in such a way that the rotation goes smoothly, without jerks, at a moderate speed. The wire should go to the top of the frame from the top of the coil. There must be at least 20 cm between the wire and the table (otherwise, you will not be able to place the hand, which will have to be guided by the wire, on the table).
The scheme of continuous winding.
Insulating gaskets and everything else should be prepared in advance and placed on the same table in reach. You may need a pencil and paper, scissors, fine sandpaper, insulating materials, a soldering iron included in the network.
One hand needs to rotate the winding device, the other hand - to direct the wire so that it lies on the frame of the coil to the coil.
Before winding, the transformer frame should be covered with insulation of the same type that will be between the windings (you may have to glue it). The lead end of the wire is passed through a hole in the frame and is temporarily fixed on the axis of the winding device.
The winding process must be started slowly: it is necessary to “wind up” to lay the turns close to each other, so that the next one presses the previous ones. The tension level of the wire and its angle must always be kept approximately constant. At the same time, each layer of turns should not be “fully supported”: there should not be a risk of sliding of the turns and falling along the frame cheek.
The counting device, if any, is necessary before starting to set to zero (or mark the value present on it). If it does not exist, it is necessary to carefully read the coils and layers of the winding, fixing their number on paper. If it is necessary to suspend work (for example, to install an insulating gasket), the wire should be left taut, otherwise the coils may disband! To do this, you can simply fix the wire relative to the frame with a linen clip.
Scheme homemade devices for winding transformers.
The insulating gasket is either glued together (so that it does not unwind, while it is not pressed yet by the next row of turns), or it is pressed against an elastic rubber ring. Flexible insulating tubes are worn on the lead ends of the wire at the beginning and end of the windings.
It is recommended that each next row of windings be made narrower: do not screw up 1-2 turns. There is no need to leave free space, it must be filled, depending on the thickness of the wire, with threads or twine. This is especially important if there is any doubt about the strength of the transformer frame.Back to table of contents
In the event of a wire breakage during winding (or if the transformer was originally planned to be wound from several separate wire fragments), the soldering process is performed differently depending on the thickness of the wire.
If the wire is medium in thickness (up to 0.3 mm), then the ends are freed from insulation (sanding) 1-1.5 cm from the point of breaking. After that, the ends are twisted and soldered.
Thick wires (more than 0.3 mm) can be soldered directly, without twisting. Accordingly, a shorter piece of wire can be released from the insulation.
Thin wires (0.1 mm and less) can not be soldered, but welded. To do this, twisting them in the same way as wires of medium thickness (but stripping insulation in this case is not needed), you need to place a spirit lamp, several matches or a gas torch into the flame. With successful welding in place of the twist formed a metal "ball".
In all cases, the place of soldering / welding is isolated with a varnished cloth or a piece of insulating paper.Back to table of contents
If the winding is made with a thin wire (less than 0.1 mm), you need to make several thousand turns, then in this case it can be done not in the “turn to turn” mode, but “in bulk”. Of course, at the same time, it is still necessary to observe approximately equal thickness of the layers. The winding should remain flat, after each mm an insulating gasket should be put.
If the winding is made of thick wire, outside it can be covered with nothing. If the wire is thin, then the outer winding should be wrapped with leatherette or insulating paper.