Transformer 12 to 220 volt do it yourself
A novice radio amateur will be able to make a transformer from 220 to 12 volts by himself. This device belongs to the machines of alternating current, the principle of operation is vaguely reminiscent of an asynchronous motor. Of course, you can buy a ready-made transformer, but why spend money, especially in those cases when there is a sufficient amount of steel on hand for the core and the wire for the coils? It remains only to study a bit of theory and you can begin to manufacture the device.
How to pick up materials
In the manufacture of step-down transformer from 220 to 12 volts, it is important to use high-quality materials - this will ensure high reliability of the device, which you will subsequently assemble on it. It should be noted that the transformer allows you to make a decoupling with the network, so it is allowed to install it to power incandescent lamps and other devices that are located in rooms with high humidity (showers, basements, etc.). When self-fabricating the coil frame, you need to use durable cardboard or textolite.
It is recommended to use domestic wires, they are much stronger than their Chinese counterparts, they have better insulation. You can use the wire from old transformers, as long as there is no damage to the insulation. To isolate the layers from each other, you can use both plain paper (preferably thin) and FUM tape, which is used in plumbing. But to insulate the windings, it is recommended to use a cloth soaked in varnish. On top of the windings it is imperative to apply insulation - lacquer cloth or cable paper.
How to carry out the calculation?
Now that all materials are ready, it is possible to calculate the transformer from 220 to 12 Volts (for a lamp or any other household appliance). In order to calculate the number of turns of the primary winding, you need to use the formula:
N = (40..60) / S.
S is the sectional area of the magnetic circuit, the unit of measurement is square. see. The numerator is a constant - it depends on the quality of a metal core. Its value may lie in the range from 40 to 60.
Calculation by example
Suppose we have the following parameters:
- The window is 53 mm high and 19 mm wide.
- The frame is made of PCB.
- Upper and lower cheeks: 50 mm, frame 17.5 mm, therefore, the window has a size of 50 x 17.5 mm.
Next, you need to calculate the diameter of the wires. Suppose you need a power of 170 watts. In this case, the current on the mains winding will be equal to 0.78 A (the power is divided by the voltage). In the design, the current density is 2 A / sq. mm With this data, you can calculate that you need to apply a wire with a diameter of 0.72 mm. It is allowed to use 0.5 mm, 0.35 mm, but the current will be less.
From this we can conclude that, for example, to power the radio equipment on lamps, you need to wind 950-1000 turns for high-voltage winding. For the heat - 11-15 turns (the wire only needs to be used with a larger diameter, depending on the number of lamps). But all these parameters can be found and empirically, which will be discussed later.
Calculation of the primary winding
In the manufacture of their own transformer with 220 to 12 volts, you need to correctly calculate the primary (mains) winding. And only after that you can start doing the rest. If you incorrectly make the calculation primary, then the device will begin to warm up, to buzz heavily, it will be inconvenient and dangerous to use it.Suppose used for winding a wire with a cross section of 0.35 mm. On one layer will fit 115 turns (50 / (0.9 x 0.39)). The number of layers is also easy to calculate. To do this, it is enough to divide the total number of turns by how much it fits in one layer: 1000/115 = 8.69.
Now you can calculate the height of the frame with the windings. Primary has eight full layers, plus there is more insulation (thickness 0.1 mm): 8 x (0.1 + 0.74) = 6.7 mm. To avoid high-frequency interference, the power winding is shielded from the rest. For the screen, you can use a simple wire - wind one layer, isolate it and connect the ends with the body. Foil can also be used (of course, it must be durable). In general, the primary winding of our transformer will take 7.22 mm.
A simple way to calculate secondary windings
And now how to calculate the secondary windings, if the primary one is already available or ready. You can use such a transformer 220 at 12 volts for LED strips, just be sure to install a voltage stabilizer. Otherwise, the brightness will be variable. So, what is needed for the calculation? A few meters of wire and just winding a certain number of turns over the primary winding. Suppose you wound 10 (and more is not needed, this is enough).
Next, you need to assemble a transformer and connect the primary winding to the network through a circuit breaker (for backup). Connect a voltmeter to the secondary winding and click the automat. See what voltage the instrument displays (for example, it showed 5 V). Consequently, each turn produces exactly 0.5 V. And now you just focus on what voltage you need to get (in our case, this is 12 V). Two turns is 1 volt voltage. And 12 V is 24 turns. But it is recommended to take a small margin - about 25% (and this is 6 turns). Nobody canceled the voltage loss, so the 12 V secondary winding should contain 30 turns of wire.
How to make a frame coils
It is extremely important in the manufacture of the frame to achieve a complete absence of sharp corners, otherwise the wire may be damaged, and an inter-turn short circuit will appear. On the cheeks you need to take places to which the output contacts from the windings will be attached. After the final assembly of the frame, it is necessary to round off all sharp edges with the help of a file.
Plates of transformer steel should enter the holes as tightly as possible, there is no free wheeling allowed.For winding thin wires, you can use a special device with a manual or electric drive. And thick wires need to be wound only by hands without additional devices.
By itself, to produce a constant current transformer 220 at 12 volts will not, you need to use additional devices. This rectifier, filter and stabilizer. The first is performed on one or more diodes. The most popular scheme is pavement. It has many advantages, among the main ones - minimum voltage loss and high quality of the output current. But it is allowed to use other rectifier circuits.
As filters, an ordinary electrolytic capacitor is used, which allows you to get rid of the residuals of the variable component of the output current. A zener diode installed at the output keeps the voltage at the same level. In this case, even if there are pulsations in the 220 V network and in the secondary winding at the output of the rectifier, the voltage will always have the same value. This has a good effect on the work of devices that connect to it.