Each of us knows what a transformer is. It serves to convert the voltage to a greater or lesser value. When we purchase a transformer in specialized stores, as a rule, the instructions for them have a full technical description. You do not need to consider all its parameters and measure them, since they are all calculated and derived by the manufacturer. In the manual, you can find parameters such as transformer power, input voltage, output voltage, number of secondary windings, if their number exceeds one.

The main parts of the design of the transformer.

## What to do if you purchased used equipment?

**But if the already used equipment fell into your hands and you do not know its functionality, you need to independently calculate the transformer winding and its power.** But how to calculate the transformer winding and its power at least approximately? It is worth noting that such a parameter as the transformer power is a very important indicator for this device, since it will depend on it how functional the device assembled from it will be. Most often it is used to create power supplies.

Calculation of power of various transformers.

First of all, it should be noted that the power of the transformer depends on the current and voltage consumed, which are necessary for its operation. In order to calculate the power, you need to multiply these two indicators: the strength of the current consumed and the supply voltage of the device. This formula is familiar to everyone from school, it looks like this:

P = Un * In, where

Un is the supply voltage, measured in volts, In is the power of the current consumed, measured in amperes, P is the power consumed, measured in watts.

If you have a transformer that you would like to measure, you can do it right now using the following method. First you need to inspect the transformer itself and determine its type and cores used in it. Looking at the transformer, it is necessary to understand what type of core is used in it. The most common is the W-type core.

This core is used in not the best transformers, in terms of efficiency, but you can easily find them on the shelves of electronics stores or unscrew them from old and faulty equipment. Availability and rather low price make them quite popular among fans to assemble a device with their own hands. You can also purchase a toroidal transformer, sometimes called a ring transformer. It is much more expensive than the first and has the best efficiency and other quality indicators, is used in fairly powerful and high-tech devices.

Back to table of contents## Independent calculation of transformer power winding

Calculation of the winding of the welding transformer.

Using books on radio engineering and electronics, we can independently calculate the winding and power of a transformer with a standard W-shaped core. In order to calculate the power of a device such as a transformer, it is necessary to correctly calculate the cross section of the magnetic circuit. As for standard transformers with an W-shaped core, the size of the cross section of the magnetic circuit will be measured by the length of the supplied plates made of special electrical steel. So, in order to determine the cross section of the magnetic circuit, it is necessary to multiply two indicators such as the thickness of the set of plates and the width of the central lobe of the W-shaped plate.

Taking a ruler, we can measure the width of the set of the emitted transformer. It is very important that all measurements are best carried out in centimeters, as well as calculations. This can eliminate the appearance of errors in the formulas and will save you from unnecessary calculations in translations from centimeters to meters. So, figuratively take a width of rows equal to three centimeters.

Next, you need to measure the width of its central lobe. This task can be a problem, since many transformers can be covered by a plastic frame due to their technological features. In this case, you will not be able, without seeing the real width, to make any calculations that at least closely look like real ones. In order to measure this parameter, you will need to look for places where it would be possible to do it. Otherwise, you can carefully disassemble its case and measure this parameter, but you should do it with jewelery accuracy.

Back to table of contents## Power calculation formula

Simplified calculation of power transformer.

Finding an open space or disassembling the device, you can measure the thickness of the central lobe. Abstract we take this parameter equal to two centimeters. It is worth recalling that, approximately calculating the power, it is necessary to take measurements as accurately as possible. Next, you need to multiply the size of the set of the magnetic circuit, equal to three centimeters, and the thickness of the lobe of the plate, equal to two centimeters. As a result, we get a section of the magnetic circuit in six square centimeters. To do further calculations, you need to familiarize yourself with such a formula as S = 1.3 * √Ptr, where:

- S is the sectional area of the magnetic circuit.
- Ptr is the power of the transformer.
- The coefficient of 1.3 is the average value.

Recalling the formulas from the course of mathematics, we can conclude that, in order to calculate the power, we can do the following transformation:

〖Ptr = (S / 1.33)〗 ^ 2

The next step is the substitution in the formula of the resulting value of the cross section of the magnetic circuit in 6 square centimeters, in the end we get the following value:

〖Ptr = (S / 1.33)〗 ^ 2 = (6 / 1.33) ^ 2 = 〖4.51〗 ^ 2 = 20.35 W

After all the calculations, we get an abstract value of 20.35 watts, which will be hard to find in a transformer with an W-shaped core. Real values fluctuate around seven watts. This power will be quite enough to assemble a power unit for equipment operating at audio frequencies and having a power ranging from 3 to 5 watts.

Back to table of contents## Fastening the material covered by the power calculation

To consolidate the material covered, you should try this method on another type of instrument.

Calculation of the welding transformer.

Take a low-power transformer and try to calculate the transformer winding according to the technology already studied. As it becomes clear from the formula, the transformer power is directly proportional to the area of its winding, from which it can be concluded that low-power transformers have smaller sizes. Take one of these representatives and measure the size of the central lobe. Figuratively, this figure will be equal to 5 millimeters.

Further, if this equipment is not difficult to measure the width of a set of plates, then you can immediately do the calculations. If you encountered any obstacles on your way, as described in the first case, then you will have to do the same procedures. After all the actions, you still measured this parameter, figuratively select a width equal to two centimeters. In this case, you have to multiply these two figures, and you get a section with a size of one square centimeter.

Using the formula for calculating power, you can determine that the power of such a transformer is 0.56 watts. Of course, as expected, its power is small enough for any serious devices. It can contain two secondary windings with the maximum allowable current value in them in a couple of tens of milliamperes. Such a transformer can only be suitable for devices that do not require a large current consumption.

If you really want to do the right calculation, which will show its real power, then you have to do additional calculations. So, for example, they have not yet invented and, most likely, in the near future, they will not be able to find an environment that would transfer electricity without loss. In any wire should take into account such factors as losses. For example, if you do counting in a rather massive transformer, then, accordingly, the losses in it will be much greater than in a transformer with a small winding. Using these formulas, you can always easily and quickly perform the necessary calculations for the power of the transformer.