Step-down transformer: the phenomenon of electromagnetic induction, the assembly of the 220 to 12 volt device

The apartment has a household outlet. Requires a low power low voltage halogen lamp to be powered. How to do it? No way, if you don't have a special device at hand that lowers the mains voltage to the required level. One of these devices is a step-down transformer from 220 to 12 volts.

Principle of operation

Translated from Latin, the word transformare means "to transform". The transformer is designed to change the supplied voltage. If the input voltage is greater than the output voltage, the transformer is called a step-down transformer. If the value of the electrical supply at the input of the device is less than at the output, then this is a step-up transformer.

The principle of operation of the device is based on the effect of electromagnetic induction. The meaning of a physical phenomenon is that an electric current occurs in a conductor, which is placed in a magnetic field that changes over time. The natural phenomenon was discovered by Michael Faraday in 1831.

An alternating current is supplied to the primary inductor of the transformer device. A magnetic field is generated in the metal core, which changes with the frequency of the applied voltage. An induction current appears in the secondary winding, the strength of which depends on the ratio of the number of turns of the incoming and outgoing coils.

The main parameters characterizing the functionality of the transformer are considered to be the input and output voltage, as well as the power of the device. The last indicator, which is the main criterion when choosing a device, determines the size of the connected load. The connected device must have a power 20% less than the norm specified in the technical passport of the transformer.

The core of the device is made of ferrite, electrical steel or permalloy. For winding, a copper conductor in varnish or paper insulation is used. High power devices are supplied with an oil cooling system.

In electrical engineering, there are three types of transformers:

1. Rod. The core is located inside the windings.
2. Armored. Most of the winding is covered with a magnetic circuit.
3. Toroidal. The magnetic system is made in the form of a ring.

All versions of 220 to 12 transformers work according to the same principle. However, a 220 volt toroidal transformer has a higher efficiency, is more compact in volume and requires fewer materials for production.

During operation the transformer is connected to the grounding bus in order to avoid electric shock to a person in an emergency. Maintenance of the unit consists in periodic inspection and cleaning of dirt and dust. In the event of a break in the winding and a short circuit, the device is dismantled and the damaged circuit is rewound.

DIY making

Electronic transformers are used to reduce the output voltage in electrical systems. The device is assembled from semiconductors and integrated circuits. With high efficiency, the device of small size and weight does not heat up and does not make noise.

However, devices of traditional design are still in demand due to their reliability and ease of manufacture. Industrial devices cost about 600 rubles. But a person with skillful hands is able to make a step-down transformer from 220 to 12 volts on his own.

Calculation of parameters

Before starting work, the technical characteristics of the transformer are calculated. First of all, the master is determined with the power of the load that will be connected to the device. In this case, it is necessary to take into account heat losses, which reduce the efficiency of the device to 80%.

To obtain the true value of the required power, divide the load power by a factor of 0.8. The remaining parameters of the transformer are calculated from this value:

1. The cross-sectional area of ​​the magnetic circuit is calculated by the formula: S = 1.2 * √P, where S is the core area, P is the power of the connected device.
2. At the next stage, the number of turns per 1 volt of voltage is determined with this core: W = 50 / S, where W is the number of turns.
3. The number of turns in each coil of the transformer is calculated as follows: N = U * W, where N is the required number of turns, U is the voltage in the winding.
4. To determine the diameter of the wire, you need to know the current strength, for the calculation of which they use the equation I = P / U, where I is the current in the coil.
5. Electrical theory indicates that for a copper conductor, the current density is 2 A / mm². With this constant, the required wire cross-section is determined as follows: D = 0.8√I, where D is the wire diameter, I is the calculated current in the winding.

For example, you need to connect a sixty-watt radio receiver operating at twelve-volt voltage. It is necessary to calculate and assemble a 12 volt step-down transformer. Calculations are carried out in accordance with the above steps.

Taking into account heat losses, the output power of the transformer is determined at the level of 75 W. The area of ​​the magnetic circuit will be 10.4 square centimeters.

One volt of voltage requires 4.8 turns. For the primary winding, 1056 turns are wound, for the output coil - 58. When the load is connected, part of the voltage is lost in the secondary inductor due to the resistance of the conductor, so add 10% to the resulting number. A total of 65 turns.

To select the cross-section of the conductor, you need to know the strength of the passing current. A current of 0.34 amperes flows through the incoming circuit, a current of 5 amperes flows through the outgoing circuit. Accordingly, the diameter of the wire of the primary inductor is 0.46 mm, the thickness of the conductor of the secondary winding is 1.78 mm. The resulting values ​​are rounded up.

Assembling the transformer

The assembly of a 220v to 12v step-down transformer requires a metal core, cardboard frame and copper wire. If there is a failed device with similar parameters, then the necessary components are borrowed from this design. You can pick up parts from non-working transformers with other technical characteristics. In this case, you will have to adjust the calculations.

If it is impossible to pick up components for industrial production, the parts are made from scrap materials. This process is time consuming and will require patience from the master.

The core plates are cut from used cans. Before assembling the magnetic core, the tin components are calcined in a fire, and then soot, scale and carbon deposits are removed from the surface with fine-grained sandpaper.

The frame is cut from thick cardboard. First, the vertical part is prepared. After gluing and drying, cheeks are fixed at the ends of the frame, in which holes are made for the output of the connection wires.

Purchase the required wire size from an electrical store. Winding material can be found at the flea market. Here, a conductor of good quality, and sometimes in its original packaging, is cheaper.

Having picked up the components of the required parameters, they begin to wind the conductors onto the frame. The operation is performed manually or using a winding machine, and laying the wire is recommended according to the "turn to turn" scheme. A strip of special capacitor paper is laid every two layers of winding. The ends of the conductors are pulled out through the holes in the cheeks.

Having finished working with the windings, they begin to fill the frame with core plates. After assembling the transformer, it is necessary to ring the electrical circuits with a multimeter. If the test is successful, the product is ready for use.

Connecting devices operating from a voltage of 12 volts using a step-down transformer saves electrical energy and, accordingly, money. In addition, such devices are absolutely safe during operation.