Simple tips on how to check the transformer with a multimeter for performance. How to determine the primary winding of a transformer by resistance. Simple tips on how to check the transformer with a multimeter for performance How to resistance

Nikolay Petrushov

How to deal with the windings of the transformer, how to properly connect it to the network and not "burn" and how to determine the maximum currents of the secondary windings ???
These and similar questions are asked by many novice radio amateurs.
In this article I will try to answer similar questions and, using the example of several transformers (photo at the beginning of the article), deal with each of them .. I hope this article will be useful to many radio amateurs.

To start, remember common features for armored transformers

The network winding, as a rule, is wound first (closest to the core) and has the greatest active resistance (unless it is a step-up transformer, or a transformer with anode windings).

The network winding can have taps, or consist of two parts with taps, for example.

The serial connection of the windings (winding parts) for armored transformers is carried out as usual, beginning with the end or terminals 2 and 3 (if, for example, there are two windings with terminals 1-2 and 3-4).

Parallel connection of windings (only for windings with the same number of turns), as usual, the beginning with the beginning of one winding, and the end with the end of another winding (n-n and k-k, or conclusions 1-3 and 2-4 - if for example there are identical windings with pins 1-2 and 3-4).

General rules for connecting secondary windings for all types of transformers.

To obtain different output voltages and load currents, windings for personal needs, other than those available on the transformer, can be obtained by various connections of the existing windings to each other. Consider all possible options.

Windings can be connected in series, including windings wound with wires of different diameters, then the output voltage of such a winding will be equal to the sum of the voltages of the connected windings (Ugen. = U1 + U2... + Un). The load current of such a winding will be equal to the smallest load current of the available windings.
For example: there are two windings with voltages of 6 and 12 volts and load currents of 4 and 2 amperes - as a result, we get a common winding with a voltage of 18 volts and a load current of 2 amperes.

Windings can be connected in parallel only if they contain the same number of turns , including those wound with wire of different diameters. The correctness of the connection is checked as follows. We connect together two wires from the windings and measure the voltage on the remaining two.
If the voltage is doubled, then the connection is not made correctly, in this case we change the ends of any of the windings.
If the voltage at the remaining ends is zero or so (a drop of more than half a volt is not desirable, the windings in this case will heat up at XX), feel free to connect the remaining ends together.
The total voltage of such a winding does not change, and the load current will be equal to the sum of the load currents of all windings connected in parallel.
(Igen. = I1 + I2... + In) .
For example: there are three windings with an output voltage of 24 volts and load currents of 1 ampere. As a result, we get a winding with a voltage of 24 volts and a load current of 3 amperes.

The windings can be connected in parallel-series (for parallel connection, see paragraph above). The total voltage and current will be the same as in a series connection.
For example: we have two in series and three windings connected in parallel (examples described above). We connect these two composite windings in series. As a result, we get a common winding with a voltage of 42 volts (18 + 24) and a load current in the smallest winding, that is, 2 amperes.

The windings can be connected in opposite directions, including those wound with wires of different diameters (also parallel and series-connected windings). The total voltage of such a winding will be equal to the voltage difference between the opposite windings, the total current will be equal to the winding with the smallest current load. Such a connection is used when it is necessary to reduce the output voltage of the existing winding. Also, in order to lower the output voltage of any winding, you can wind an additional winding over all the windings with a wire, preferably of no smaller diameter. the winding whose voltage needs to be lowered so that the load current does not decrease. The winding can be wound without even disassembling the transformer if there is a gap between the windings and the core , and turn it on opposite to the desired winding.
For example: we have two windings on the transformer, one 24 volts 3 amperes, the second 18 volts 2 amperes. We turn them on counter and as a result we get a winding with an output voltage of 6 volts (24-18) and a load current of 2 amperes.
But this is purely theoretical, in practice, the efficiency of such an inclusion will be lower than if the transformer had one secondary winding
The fact is that the current flowing through the windings creates an EMF in the windings, and in b O the larger winding, the voltage decreases with respect to the XX voltage, and in m e lower - increases, and the more current flowing through the windings - the greater this effect.
As a result, the total rated voltage (at the rated current) will be lower.

Let's start with a small transformer, adhering to the features described above (left in the photo).
We carefully examine it. All his conclusions are numbered and the wires are suitable for the following conclusions; 1, 2, 4, 6, 8, 9, 10, 12, 13, 22, 23, and 27.
Next, you need to ring all the conclusions with an ohmmeter to determine the number of windings and draw a transformer diagram.
It turns out the following picture.
Conclusions 1 and 2 - the resistance between them is 2.3 Ohm, 2 and 4 - between them is 2.4 Ohm, between 1 and 4 - 4.7 Ohm (one winding with an average output).
Further 8 and 10 - resistance 100.5 Ohm (another winding). Conclusions 12 and 13 - 26 Ohm (still winding). Conclusions 22 and 23 - 1.5 Ohm (last winding).
Pins 6, 9 and 27 do not ring with other pins and with each other - these are most likely screen windings between the network and other windings. These conclusions in the finished design are interconnected and attached to the body (common wire).
Once again, carefully examine the transformer.
The network winding, as we know, is wound first, although there are exceptions.

It's hard to see in the photo, so I'll duplicate it. A wire is soldered to terminal 8, coming out from the core itself (that is, it is closest to the core), then the wire goes to terminal 10 - that is, winding 8-10 is wound first (and has the highest active resistance) and is most likely network.
Now, according to the data received from the dialing, you can also draw a transformer diagram.

It remains to try to connect the proposed primary winding of the transformer to a 220 volt network and check the no-load current of the transformer.
To do this, we collect the following chain.

In series with the proposed primary winding of the transformer (we have conclusions 8-10), we connect a conventional incandescent lamp with a power of 40-65 watts (for more powerful transformers 75-100 watts). The lamp in this case will play the role of a kind of fuse (current limiter), and protect the transformer winding from failure when connected to a 220 volt network, if we have chosen the wrong winding or the winding is not designed for 220 volts. The maximum current flowing in this case through the winding (with a lamp power of 40 watts) will not exceed 180 milliamps. This will save you and the tested transformer from possible troubles.

And in general, take it as a rule, if you are not sure about the correct choice of the mains winding, its switching, in the installed winding jumpers, then always make the first connection to the network with an incandescent lamp connected in series.

Being careful, we connect the assembled circuit to a 220 volt network (I have a slightly higher network voltage, or rather, 230 volts).
What do we see? Incandescent lamp does not light.
This means that the network winding is selected correctly and further connection of the transformer can be made without a lamp.
We connect the transformer without a lamp and measure the no-load current of the transformer.

The no-load current (XX) of the transformer is measured as follows; a similar circuit is assembled that we assembled with a lamp (I won’t draw anymore), only instead of a lamp, an ammeter is turned on, which is designed to measure alternating current (carefully inspect your device for such a mode).
The ammeter is first set to the maximum measurement limit, then, if there is a lot of it, the ammeter can be transferred to a lower measurement limit.
Being careful - we connect to a 220 volt network, preferably through an isolation transformer. If the transformer is powerful, then it is better to short-circuit the ammeter probes at the time the transformer is connected to the network either with an additional switch, or simply short-circuit them together, since the starting current of the primary winding of the transformer exceeds the no-load current by 100-150 times and the ammeter may fail. After the transformer is connected to the network, the ammeter probes are disconnected and the current is measured.

The no-load current of the transformer should ideally be 3-8% of the rated current of the transformer. It is considered normal and the XX current is 5-10% of the nominal. That is, if a transformer with an estimated rated power of 100 watts, the current consumption of its primary winding will be 0.45 A, then the XX current should ideally be 22.5 mA (5% of the nominal) and it is desirable that it does not exceed 45 mA (10 % of nominal).

As you can see, the no-load current is a little more than 28 milliamps, which is quite acceptable (well, maybe a bit too high), since this transformer has a power of 40-50 watts.
We measure the open-circuit voltage of the secondary windings. It turns out at pins 1-2-4 17.4 + 17.4 volts, pins 12-13 = 27.4 volts, pins 22-23 = 6.8 volts (this is at a mains voltage of 230 volts).
Next, we need to determine the capabilities of the windings and their load currents. How it's done?
If it is possible and allows the length of the winding wires suitable for the contacts, then it is better to measure the diameters of the wires (roughly up to 0.1 mm - with a caliper and accurately with a micrometer), and according to the table, at an average current density of 3-4 A / mm.kv. - we find the currents that the windings are capable of delivering.
If it is not possible to measure the diameters of the wires, then proceed as follows.
We load each of the windings in turn with an active load, which can be anything, for example, incandescent lamps of various power and voltage (an incandescent lamp with a power of 40 watts at a voltage of 220 volts has an active resistance of 90-100 ohms in a cold state, a lamp with a power of 150 watts - 30 Ohm), wire resistances (resistors), nichrome coils from electric stoves, rheostats, etc.
We load until the voltage on the winding decreases by 10% relative to the open circuit voltage.
Then we measure the load current.

This current will be the maximum current that the winding is capable of delivering for a long time without overheating.

The value of the voltage drop up to 10% for a constant (static) load is conventionally accepted so that the transformer does not overheat. You may well take 15%, or even 20%, depending on the nature of the load. All these calculations are approximate. If the load is constant (the incandescence of lamps, for example, Charger), then a smaller value is taken, if the load is impulse (dynamic), for example ULF (with the exception of mode "A"), then you can take a value and more, up to 15-20%.

I take into account the static load, and I did it; winding 1-2-4 load current (with a decrease in winding voltage by 10% relative to the open circuit voltage) - 0.85 amperes (power about 27 watts), winding 12-13 (pictured above) load current 0.19-0, 2 amps (5 watts) and winding 22-23 - 0.5 amps (3.25 watts). The rated power of the transformer is about 36 watts (round up to 40).

Yes, I also want to talk about the resistance of the primary winding.
For low-power transformers, it can be tens or even hundreds of ohms, and for powerful transformers, it can be units of ohms.
Questions like this are often asked on the forum;
"I measured the resistance of the primary winding of the TS250 with a multimeter, and it turned out to be 5 ohms. Is it not enough for a 220 volt network, I'm afraid to turn it on. Tell me, is it normal?"

Since all multimeters measure DC resistance (resistance), there is no need to worry, because for 50 hertz AC this winding will have a completely different resistance (inductive), which will depend on the inductance of the winding and the frequency of the AC.
If you have something to measure the inductance, then you yourself can calculate the winding resistance to alternating current (inductive reactance).

For example;
The inductance of the primary winding during the measurement was 6 H, go here and enter these data (inductance 6 Gn, network current frequency 50 Hz), look - it turned out 1884.959 (round up 1885), this will be the inductive resistance of this winding for a frequency of 50 Hz. From here you can also calculate the no-load current of this winding for a voltage of 220 volts - 220/1885 = 0.116 A (116 milliamps), yes, here you can also add an active resistance of 5 ohms, that is, it will be 1890.
Naturally, for a frequency of 400 Hz there will be a completely different resistance of this winding.

Other transformers are tested in the same way.
The photo of the second transformer shows that the conclusions are soldered to the contact petals 1, 3, 4, 6, 7, 8, 10, 11, 12.
After dialing, it becomes clear that the transformer has 4 windings.
The first is on pins 1 and 6 (24 Ohm), the second is 3-4 (83 Ohm), the third is 7-8 (11.5 Ohm), the fourth is 10-11-12 with a tap from the middle (0.1 + 0.1 Ohm) .

Moreover, it is clearly seen that windings 1 and 6 are wound first (white leads), then winding 3-4 comes (black leads).
24 ohms of active resistance of the primary winding is enough. For more powerful transformers, the active resistance of the winding reaches units of ohms.
The second winding is 3-4 (83 ohms), possibly increasing.
Here you can measure the diameters of the wires of all windings, except for winding 3-4, the conclusions of which are made of black, stranded, mounting wire.

Next, we connect the transformer through an incandescent lamp. The lamp does not light up, the transformer looks like a power of 100-120, we measure the no-load current, it turns out 53 milliamps, which is quite acceptable.
We measure the open circuit voltage of the windings. It turns out 3-4 - 233 volts, 7-8 - 79.5 volts, and the winding 10-11-12 is 3.4 volts each (6.8 with an average output). Winding 3-4 is loaded until the voltage drops by 10% of the open circuit voltage, and we measure the current flowing through the load.

The maximum load current of this winding, as can be seen from the photograph, is 0.24 amperes.
The currents of the other windings are determined from the current density table, based on the wire diameter of the windings.
Winding 7-8 is wound with wire 0.4 and filament wire 1.08-1.1. Accordingly, the currents are 0.4-0.5 and 3.5-4.0 amperes. The rated power of the transformer is about 100 watts.

There is one more transformer left. He has a contact strip with 14 contacts, the top 1, 3, 5, 7, 9, 11, 13 and the bottom, respectively, are even. It could switch to different mains voltages (127,220.237) it is quite possible that the primary winding has several taps, or consists of two half-windings with taps.
We call, and we get this picture:
Pins 1-2 = 2.5 ohms; 2-3 = 15.5 ohms (this is one winding with a tap); 4-5 = 16.4 ohms; 5-6 \u003d 2.7 Ohm (another winding with a tap); 7-8 \u003d 1.4 Ohm (3rd winding); 9-10 = 1.5 ohms (4th winding); 11-12 = 5 ohms (5th winding) and 13-14 (6th winding).
We connect to pins 1 and 3 a network with a series-connected incandescent lamp.

The lamp burns at half glow. We measure the voltage at the terminals of the transformer, it is equal to 131 volts.
So they didn’t guess, and the primary winding here consists of two parts, and the connected part at a voltage of 131 volts begins to saturate (the no-load current rises) and therefore the lamp filament is heated.
We connect terminals 3 and 4 with a jumper, that is, two windings in series and connect the network (with a lamp) to terminals 1 and 6.
Hurray, the lamp is not on. We measure the idle current.

The no-load current is 34.5 milliamps. Here, most likely (as part of the winding 2-3, and part of the second winding 4-5 have more resistance, these parts are designed for 110 volts, and parts of the windings 1-2 and 5-6 are 17 volts each, that is, common for one part of 1278 volts) 220 volts was connected to pins 2 and 5 with a jumper on pins 3 and 4 or vice versa. But you can leave it the way we connected it, that is, all parts of the windings are in series. For a transformer, it's only better.
Everything, the network was found, further actions similar to those described above.

A little more about rod transformers. For example, there is one (photo above). What are their common features?

Rod transformers, as a rule, have two symmetrical coils, and the network winding is divided into two coils, that is, turns of 110 (127) volts are wound on one coil, and on the other. The numbering of the leads of one coil is similar to the other, the numbers of the leads on the other coil are marked (or conventionally marked) with a stroke, i.e. 1", 2", etc.

The network winding, as a rule, is wound first (closest to the core).

The network winding can have taps, or consist of two parts (for example, one winding - pins 1-2-3; or two parts - pins 1-2 and 3-4).

In a rod transformer, the magnetic flux moves along the core (in a "circle, ellipse"), and the direction of the magnetic flux of one rod will be opposite to the other, therefore, to connect the two halves of the windings in series, on different coils, the same-named contacts are connected or the beginning to the beginning (end to end) , i.e. 1 and 1", the network is fed to 2-2", or 2 and 2", the network is then fed to 1 and 1".

For serial connection of windings consisting of two parts on one coil - the windings are connected as usual, the beginning to the end or the end to the beginning, (n-k or k-n), that is, output 2 and 3 (if, for example, there are 2 windings with pin numbers 1-2 and 3-4), also on the other coil. Further serial connection of the resulting two half-windings on different coils, see paragraph above. (An example of such a connection is on the diagram of the transformer TS-40-1).

For parallel connection of windings ( only for windings with the same number of turns ) on one coil, the connection is made as usual (n-n and k-k, or terminals 1-3 and 2-4 - if, for example, there are identical windings with terminals 1-2 and 3-4). For different coils, the connection is made as follows, k-n-outlet and n-to- branch, or terminals 1-2 "and 2-1" are connected - if, for example, there are identical windings with terminals 1-2 and 1 "-2".

Once again, I remind you of the observance of safety precautions, and it is best to have an isolation transformer at home for experiments with a voltage of 220 volts (a transformer with 220/220 volt windings for galvanic isolation from an industrial network), which will protect against electric shock if you accidentally touch the bare end of the wire .

If you have any questions about the article, or you find a transformer in the stash (with a suspicion that it is a power one), ask questions, we will help you deal with its windings and connecting to the network.

An electrical transformer is a fairly common device used in everyday life for a number of tasks.

And breakdowns can occur in it, which can be identified by a device for measuring electric current parameters - a multimeter.

From this article you will learn how to check the current transformer with a multimeter (ring), and what rules should be followed.

As you know, any transformer consists of the following components:

primary and secondary coils (there may be several secondary ones);
core or magnetic circuit;
frame.

Thus, the list of possible breakdowns is rather limited:

Damaged core.
A wire burned out in one of the windings.
The insulation is broken, as a result of which there is an electrical contact between the turns in the coil (turn-to-turn short circuit) or between the coil and the housing.
Worn coil leads or contacts.

Current transformer T-0.66 150/5a

Some of the defects are determined visually, so the transformer must first be carefully examined. Here's what you should pay attention to:

cracks, chips of insulation or its absence;
condition of bolted connections and terminals;
swelling of the fill or its leakage;
blackening on visible surfaces;
charred paper;
characteristic smell of burning material.

If there is no obvious damage, the device should be checked for operability using instruments. To do this, you need to know which windings all of its conclusions belong to. On large transducers this information can be represented as a graphic image.

If this is not available, you can use the reference book in which you should find your transformer by marking. If it is part of an electrical appliance, the data source may be a specification or a circuit diagram.

Methods for testing a transformer with a multimeter

First of all, you should check the condition of the transformer insulation. To do this, the multimeter must be switched to megger mode. After that, measure the resistance:

between the body and each of the windings;
between the windings in pairs.

The voltage at which this test is to be carried out is specified in technical documentation to the transformer. For example, for most high-voltage models, it is prescribed to measure the insulation resistance at a voltage of 1 kV.

Checking the device with a multimeter

The required resistance value can be found in the technical documentation or in the reference book. For example, for the same high-voltage transformers, it is at least 1 mΩ.

This test is not able to detect turn-to-turn short circuits, as well as changes in the properties of wire and core materials. Therefore, it is imperative to check the performance of the transformer, for which the following methods are used:

A voltage of 220 volts is not perceived by all devices. lowers the voltage to enable the use of electrical appliances.

How to check a varistor with a multimeter and why you need a varistor, read.

You can familiarize yourself with the rules for checking the voltage in a socket with a multimeter.

Direct method (checking the circuit under load)

It is he who first comes to mind: you need to measure the currents in the primary and secondary windings of a working device, and then, by dividing them by each other, determine the actual transformation ratio. If it corresponds to the passport - the transformer is working, if not - you need to look for a defect. This coefficient can also be calculated independently if the voltage that the device should produce is known.

For example, if 220V / 12V is written on it, then we have a step-down transformer, therefore, the current in the secondary winding should be 220/12 \u003d 18.3 times higher than in the primary (the term "step-down" refers to voltage).

Scheme for verification of a single-phase transformer by direct measurement of primary and secondary voltages using a reference transformer

The load to the secondary winding must be connected in such a way that currents flowing in the windings are not lower than 20% of the nominal values. When turning on, be on your guard: if there is a crackling sound, a burning smell appears, or you see smoke or sparks, the device must be turned off immediately.

If the transformer under test has several secondary windings, then those of them that are not connected to the load must be short-circuited. In an open secondary coil, when the primary coil is connected to an alternating current source, a high voltage can appear that can not only disable equipment, but also kill a person.

Serial connection of transformer windings using a battery and a multimeter

If we are talking about a high-voltage transformer, then before turning it on, you need to check whether its core needs to be grounded. This is evidenced by the presence of a special terminal marked with the letter "Z" or a special icon.

The direct method of checking the transformer allows you to fully assess the state of the latter. However, it is far from always possible to turn on the transformer with a load and make all the necessary measurements.

If, due to safety or other reasons, this cannot be done, the condition of the device is checked indirectly.

indirect method

Part this method includes several tests, each of which displays the state of the device in one aspect. Therefore, it is desirable to carry out all these tests in combination.

Determination of the reliability of the marking of the winding leads

To perform this test, the multimeter must be switched to ohmmeter mode. Next, you need to “ring” all the available conclusions in pairs. Between those of them that belong to different coils, the resistance will be equal to infinity. If the multimeter shows a specific value, then the conclusions belong to the same coil.

Here you can compare the measured resistance with that given in the reference book. If there is a discrepancy of more than 50%, then an interturn short circuit or partial destruction of the wire has occurred.

Connecting a transformer to a multimeter

Please note that on coils with a large inductance, that is, consisting of a significant number of turns, the digital multimeter may erroneously show an overestimated resistance. In such cases, it is advisable to use an analog device.

The windings should be checked with direct current, which the transformer cannot convert. When using an alternating current, an EMF will be induced in other coils and it is quite possible that it will be quite high. So, if an alternating voltage of only 20 V is applied to the secondary coil of a 220/12 V step-down transformer, then a voltage of 367 V will appear at the primary terminals and, if accidentally touched, the user will receive a strong electric shock.

Next, you need to determine which pins should be connected to the current source, and which to the load. If it is known that the transformer is step-down, then the coil with the largest number of turns and the greatest resistance should be connected to the current source. With a step-up transformer, the opposite is true.

All methods of measuring the strength of electric current

But there are models that have both step-down and step-up coils among the secondary coils. Then the primary coil can be recognized with a certain degree of probability by the following features: its conclusions are usually mounted away from the others, and the coil can also be located on the frame in a separate section.

The development of the Internet has made this method possible: you need to take a picture of the transformer and write a request with the attached photo and all the available information (brand, etc.) to one of the network thematic forums.

Perhaps one of its participants has dealt with such devices and can tell in detail how to connect it.

If there are intermediate taps in the secondary coil, its beginning and end must be recognized. To do this, you need to determine the polarity of the outputs.

Determining the polarity of the winding leads

In the role of a meter, you should use a magnetoelectric ammeter or voltmeter, in which the polarity of the leads is known. The device must be connected to the secondary coil. It is most convenient to use those models in which "zero" is located in the middle of the scale, but in the absence of such, the classic one is also suitable - with the location of "zero" on the left.

If there are several secondary coils, the others must be shunted.

Checking the polarity of the phase windings of electrical AC machines

Pass through the primary coil D.C. little strength. An ordinary battery is suitable for the role of a source, while a resistor must be included in the circuit between it and the coil - so that a short circuit does not occur. An incandescent lamp can serve as such a resistor.

It is not necessary to install a switch in the circuit of the primary coil: it is enough to follow the arrow of the multimeter to close the circuit, touching the wire from the coil output lamp, and immediately open it.

If the same poles from the battery and the multimeter are connected to the terminals of the coils, that is, the polarity is the same, then the arrow on the device will twitch to the right.

With bipolar connection - to the left.

At the moment of power off, the opposite picture will be observed: with a unipolar connection, the arrow will move to the left, with a bipolar connection - to the right.

On a device with a “zero” at the beginning of the scale, the movement of the arrow to the left is more difficult to notice, since it almost immediately bounces off the limiter. Therefore, you need to watch carefully.

In the same way, the polarities of all other coils are checked.

A multimeter is a very necessary device for measuring current strength, which is used to troubleshoot certain devices. – read helpful tips optionally.

Instructions for checking diodes with a multimeter are presented.

Removing the magnetization characteristic

To be able to use this method, you need to prepare ahead of time: while the transformer is new and known to be in good condition, its so-called current-voltage characteristic (CVC) is taken. This is a graph showing the dependence of the voltage at the terminals of the secondary coils on the magnitude of the magnetization current flowing in them.

Schemes of removal of characteristics of magnetization

Having opened the circuit of the primary coil (so that the results are not distorted by interference from nearby power equipment), they pass through the secondary alternating current different strength, each time measuring the voltage at its input.

The power used for this power supply must be sufficient to saturate the magnetic circuit, which is accompanied by a decrease in the slope of the saturation curve to zero (horizontal position).

Measuring instruments must refer to an electrodynamic or electromagnetic system.

Before and after the test, the magnetic circuit must be demagnetized by increasing the current strength in the winding in several approaches, followed by its decrease to zero.

As the device is used, it is necessary to take the current-voltage characteristic with a certain frequency and compare it with the original one. A decrease in its steepness will indicate the appearance of an interturn short circuit.

The most important parameters of power transformers

What do you need to know about the transformer in order to correctly and, most importantly, safely use it for your own purposes? Most of the time it's a repair. household appliances or making your own crafts powered by low voltage. And you need to know the following about the transformer lying in front of us:

Which terminals to supply mains power (230 volts) to?
From which conclusions to remove the low voltage?
What will it be (12 volts, 24 or other)?
How much power can the transformer deliver?
How not to get confused if there are several windings, and, accordingly, pairwise conclusions?

All these characteristics are quite realistic to calculate even when there is absolutely no information about the brand and model of the power transformer.
To do the job, you will need the simplest tools and supplies:

multimeter with ohmmeter and voltmeter functions;
soldering iron;
electrical tape or heat shrink tubing;
mains plug with wire;
a pair of ordinary wires;
incandescent lamp;
calipers;
calculator.

You will also need some kind of wire stripping tool and a minimal soldering kit - solder and rosin.

Definition of primary and secondary windings

The primary winding of the step-down transformer is designed to supply mains power. That is, it is to it that you need to connect 230 volts, which are in a regular household outlet. In the most simple options the primary winding can have only two outputs. However, there are also those in which there are, for example, four conclusions. This means that the product is designed to work from both 230 V and 110 V. We will consider a simpler option.
So, how to determine the conclusions of the primary winding of the transformer? To solve this problem, you need a multimeter with an ohmmeter function. With it, you need to measure the resistance between all available outputs. Where it will be the most, there is the primary winding. It is advisable to immediately mark the findings found, for example, with a marker.

The primary winding can be determined in another way. To do this, the wound wire inside the transformer must be clearly visible. In modern versions, this is most often the case. In older products, the insides may be filled with paint, which excludes the use of the described method. The winding with the smaller wire diameter is visually highlighted. She is primary. It needs to be supplied with mains power.
It remains to calculate the secondary winding, from which the reduced voltage is removed. Many have already guessed how to do it. Firstly, the resistance of the secondary winding will be much less than that of the primary. Secondly, the diameter of the wire with which it is wound will be larger.

The task becomes a little more complicated if the transformer has several windings. This option is especially scary for beginners. However, the method of their identification is also very simple, and is similar to that described above. First of all, you need to find the primary winding. Her resistance will be many times greater than that of the rest.
At the end of the topic on transformer windings, it is worth saying a few words about why the resistance of the primary winding is greater than that of the secondary, and with the wire diameter everything is exactly the opposite. This will help beginners to understand the issue in more detail, which is very important when working with high voltage.
A mains voltage of 220 V is supplied to the primary winding of the transformer. This means that with a power of, for example, 50 W, a current of about 0.2 A will flow through it (we divide the power by voltage). Accordingly, a large cross section of the wire is not needed here. This is, of course, a very simplified explanation, but for beginners (and the solution of the problem posed above), this will be enough.
In the secondary winding, currents flow more significant. Let's take the most common transformer that delivers 12 V. With the same power of 50 W, the current flowing through the secondary winding will be about 4 A. This is already quite a large value, because the conductor through which such a current will pass must be thicker. Accordingly, the larger the cross section of the wire, the less resistance it will have.
Using this theory and a simple ohmmeter, you can easily calculate where the winding of a step-down transformer without marking is.

Determining the voltage of the secondary winding

The next step in identifying the "nameless" transformer will be to determine the voltage on its secondary winding. This will determine whether the product is suitable for our purposes. For example, you are assembling a 24 V power supply, and the transformer only outputs 12 V. Accordingly, you will have to look for another option.

To determine the voltage that can be removed from the secondary winding, the transformer will have to be supplied with mains power. This is already quite a dangerous operation. By negligence or ignorance, you can get a strong electric shock, burn yourself, damage the wiring in the house, or burn the transformer itself. Therefore, it will not be superfluous to stock up on a few recommendations regarding safety precautions.
Firstly, when testing, the transformer should be connected to the network through an incandescent lamp. It is connected in series, in the gap of one of the wires going to the plug. The light bulb will serve as a fuse in case you do something wrong, or if the transformer under study is faulty (short-circuited, burned out, wet, and so on). If it glows, then something went wrong. There is a short circuit in the transformer, so it is better to pull the plug out of the socket immediately. If the lamp does not glow, does not stink or smoke, work can be continued.
Secondly, all connections between the outlets and the plug must be carefully insulated. Do not neglect this recommendation. You will not even notice how, considering the readings of the multimeter, for example, you will undertake to correct twisted wires, you will get a pretty electric shock. This is dangerous not only for health, but also for life. For insulation, use electrical tape or heat shrink tubing of the appropriate diameter.
Now the process itself. A conventional plug with wires is soldered to the terminals of the primary winding. As stated above, an incandescent lamp is added to the circuit. All connections are isolated. A multimeter in voltmeter mode is connected to the terminals of the secondary winding. Please note that it is turned on for measuring AC voltage. Beginners often make a mistake here. By setting the multimeter pen to measure DC voltage, you will not burn anything, however, you will not get any sane and useful readings on the display.

Now you can insert the plug into the socket. If everything is in working condition, then the device will show you the reduced voltage generated by the transformer. Similarly, you can measure the voltage on other windings, if there are several.

Simple ways to calculate the power of a power transformer

With the power of a step-down transformer, things are a little more complicated, but there are still some simple techniques. Most affordable way determine this characteristic - measuring the diameter of the wire in the secondary winding. To do this, you will need a caliper, a calculator and the information below.
First, the diameter of the wire is measured. For example, take a value of 1.5 mm. Now you need to calculate the cross section of the wire. To do this, you need to square half the diameter (radius) and multiply by the number "pi". For our example, the cross section will be about 1.76 square millimeters.
Further, for the calculation, you will need the generally accepted value of current density per square millimeter of conductor. For household step-down transformers, this is 2.5 amperes per millimeter square. Accordingly, a current of about 4.3 A can “painlessly” flow through the second winding of our sample.
Now we take the previously calculated voltage of the secondary winding, and multiply it by the resulting current. As a result, we get the approximate value of the power of our transformer. At 12 V and 4.3 A, this parameter will be around 50 watts.
The power of the "nameless" transformer can be determined in several other ways, however, they are more complex. Those who wish can find information about them on the Web. Power is recognized by the cross section of the transformer windows, using calculation programs, as well as by the nominal operating temperature.

Conclusion

From the foregoing, we can conclude that determining the characteristics of a transformer without marking is a fairly simple task. The main thing is to follow safety rules and be extremely careful when working with high voltage.