How to calculate the transformer?

Electrical apparatus - transformerUsed to convert incoming AC voltage to other - outgoing, for example: 220 V to 12 V (specifically this conversion is achieved using a step-down transformer). Before you figure out how to calculate a transformer, you must first have knowledge about its structure.

The simplest transformer is a layoutmagnetic core and windings of 2 types: primary and secondary, specially wound on it. The primary winding senses the AC supply voltage from the mains (eg: 220 V), and the secondary winding, by inductive coupling, creates another alternating voltage. The difference in turns in the windings affects the output voltage.

W-shaped transformer

1. Consider, for example, the process of calculating the usualШ-shaped transformer. Suppose given the following parameters: load current i2 = 0.5A, output voltage (secondary voltage) U2 = 12V, mains voltage U1 = 220V.
2. The first indicator determines the output power: P2 = U2ˣi2 = 12ˣ0.5 = 6 (W). This means that this power provides for the use of a magnetic circuit with a cross section of about 4 cm² (S = 4).
3. Then determine the number of turns needed for one volt. The formula for this type of transformer is: K = 50 / S = 50/4 = 12.5 (turns / volts).
4. Then, the number of turns in the primary winding is determined: W1 = U1ˣK = 220ˣ12.5 = 2750 (turns). And then the number of turns located in the secondary winding: W2 = U2ˣK = 12ˣ12.5 = 150.
5. The current that occurs in the primary winding,calculate this: i1 = (1,1 × P2) / U1 = (1,1 × 6) /220=30mA. This will allow you to calculate the diameter of the wire laid in the primary winding and not equipped with insulation. It is known that the maximum current for a copper wire is 5 amperes per mm2, which implies that: d1 = 5A / (1 / i1) = 5A / (1 / 0.03A) = 0.15 (mm) .
6. The last step is to calculate the diameter of the secondary wire using d2 = 0.025ˣ√i2, with i2 being used in milliamperes (mA): d2 = 0.025ˣ22.4 = 0.56 (mm).

How to calculate the power of a transformer

1. The voltage available on the secondary winding and maxknow the load current in advance. Then multiply the factor 1.5 by the current of the maximum load (measured in amperes). So you determine the winding of the second transformer (also in amperes).
2. Determine the power that the rectifier consumes from the secondary winding of the transformer being calculated: multiply the maximum current passing through it to the voltage of the secondary winding.
3. Calculate the power of the transformer by multiplying the maximum power on the secondary by 1.25.

If you need to determine the powertransformer, which is required for specific purposes, then it is necessary to summarize the power of the installed energy-consuming devices with 20%, in order for it to have a reserve. For example, if you have a 10m LED strip consuming 48 watts, then you need to add 20% to this number. It turns out 58 watts - the minimum power of the transformer, which will need to be installed.

How to calculate the current transformer

The main characterizing feature of the transformer is the transformation ratio, which indicates how much the main current parameters will change, as a result of its passage through this device.

If the ratio of transformation exceeds 1, then the transformer is decreasing, and if less than this index, then it is raising.

1. A conventional transformer is formed from two coils. Determine the number of turns of the coils N1 and N2, which are connected by a magnetic core. Find the transformation ratio k by dividing the number of turns of the primary coil N1 connected to the current source by the number of turns of coil N2 to which the load is connected: k = N1 / N2.
2. Measure electromotive force (EMF) onboth transformer windings ε1 and ε2, if it is not possible to determine the number of turns in them. You can do it this way: connect the primary winding to the current source. The so-called idling turns out. Using a tester, determine the voltage on each winding. It will correspond to the EMF of the measured winding. Do not forget that the resulting energy losses due to the resistance of the windings are so small that they can be neglected. The coefficient of transformation is calculated through the ratio of the EMF of the primary winding to the EMF secondary: k = ε1 / ε2.
3. Find the ratio of the transformation inoperation of the transformer when the consumer is connected to the secondary winding. Determine it by dividing the current in the primary I1 winding, on the current generated in the secondary I2 winding. Measure the current by sequentially attaching the tester (switched to the ammeter operation mode) to the windings: k = I1 / I2.