Thyristor instead of latr color scheme. Latr (laboratory autotransformer). Autotransformers have a wide range of uses in various fields of human activity

A laboratory autotransformer, or LATR for short, is a device for changing the alternating current voltage of various electrical appliances. This device is a type of ordinary transformer. During the process of changing voltage using LATR, the frequency of the device at any stage remains the same. His work is based on the phenomenon of electromagnetic induction. The device includes many additional modifications.

Autotransformer device

There is one common winding located on the magnetic core of the LATR, and three additional terminals extend from it. For older models, the autotransformer A current-collecting contact is located on the secondary winding, allowing:

• output voltage is smoothly adjustable;
• at one moment change one voltage value to another;
• change the heating intensity of the soldering iron tip;
• regulate electric lighting.

The most common type of autotransformer is a toroidal magnetic circuit. It is a ring-shaped core made of electrical steel.

Copper wire, or winding, is wound around the core. In addition, the design of the device has an additional tap - a tap from the winding. In total, there are exactly three contacts.

For large transformations, it is best not to use LATR. The reasons are as follows:

1. The chances of resulting in a short circuit are too high. Electronic circuits specially adapted for this purpose or additional resistance will help deal with the problem.
2. A conventional transformer is more suitable for many reasons, such as higher efficiency, lower steel costs, reduced dimensions and weight, and reduced tool costs.

Electronic device circuit

Buying a reliable LATR with the available assortment is not an easy task. There are too many low quality products on the market. As an option, you can purchase an industrial design, but the prices are quite high, and the dimensions are rather large. In this case, a more acceptable option would be to create an autotransformer with your own hands.

Materials required for assembly

Materials you will definitely need for assembling a homemade electronic LATR on a field-effect transistor, the following:

• copper wire (winding);
• heat-resistant varnish;
• rag tape;
• magnetic circuit (both rod and toroidal types are suitable);
• a housing with fixed connectors to which power and load will be connected.

LATR winding calculation

Next, add a housing to the autotransformer and make a mount for the regulator handle. Attach a slider with a carbon brush to the handle. You need to make sure that the brush touches the top of the winding tightly. The area over which the brush will move must be marked, and the insulation at the marking location must be removed. So, the brush will have direct electrical contact with the secondary winding. The secondary voltage terminals, in addition to the common one, are shaded with one connected to a carbon brush. When connected, the voltmeter is fixed.

Now you need to make sure that the autotransformer works as it should. To check the quality of the device, perform the following steps:

If no problems are found, then the laboratory autotransformer is completely ready for use.

In the laboratory stands of my college, laboratory autotransformers (LATRs) regularly fail. It so happened that through trial and error I managed to master the technology for repairing them. At the moment, I have already managed to repair three laboratory autotransformers, and I rewound the LATRs in my dorm room. I would be glad if the technology for rewinding LATRs outlined here turns out to be useful to someone. Yes, this is my first article, so don't judge too harshly :-)

First, a short course on the LATR device (see picture).

LATR has two windings connected in series. Mains voltage is supplied to the primary winding (this must be taken into account when rewinding). The secondary winding is connected to the primary. It is designed for voltage from 0-240 V. Voltage is applied to terminals A and N in the magnetic circuit, creating a magnetic flux that induces current in the windings taken from terminals A1 and N.

Let's start by determining the diameter of the wire. This can be done using a caliper. To do this, you first need to measure the diameter of the original wire, and then, based on this, look for the wire that suits us. You can take a piece of old wire and then compare it with the desired sample.

Then you need to determine the length of the wire. This can be done using the usual mathematical expression: L=lturn×W 1.2 cm,

where L is the required wire length (in centimeters), lturn is the length of one turn; W 1.2 - number of turns of the secondary and primary windings.

1) Calculation of the number of turns using formulas. This method is quite simple, but there is a high probability of errors, for example in calculations or in measurements of the area of ​​the magnetic circuit window. This method is given below:

Find the power of the autotransformer: P=U×I,

where U is the output voltage, I is the maximum load current (usually written in LATR).

The overall power is: Рг=1.9* Sc * S,

where 1.9 is the coefficient used for toroidal transformers.

Required number of turns per 1 volt:

K = 35/Sc, where 35 is the coefficient used for torroidal transformers.

Determine the number of turns; W1 = U1*K

We determine the dimensions of the core: Sc=((Dc-dc)/2)×h, So=πxd2/4,

where Sc is the area of ​​the transformer core; So is the window area.

2) The second option is quite labor-intensive, but reliable (when rewinding LATRs, I used this method). This method of determining the number of turns is that you need to unwind the old winding and at the same time count the number of turns. It requires: a leaf and a handle so as not to get lost, a reel or piece of wood to wind the old winding there, as well as nerves of steel and patience so as not to throw it out the window after a hundred counted turns.

After this, we rest and relax after the work done, because then we need maximum attentiveness and patience. When you have rested, we begin to prepare the workplace. It is desirable that it be well lit and that all the necessary items can be placed, for example, a desk with a lamp or a chair in a room with good lighting.

For ease of rewinding, it is better to first wind the new wire on a wooden block as shown in the picture:

There is no fundamental difference in how the wire is laid out on the inner diameter of the window. But in order to lay the required number of turns, it is necessary to wind the first turn tightly to it, then wind the second turn, and lay the third turn on top between the first and second and repeat until we have wound the required number of turns at a voltage of 220V. After this, we make a terminal for the network terminal and wind the secondary winding from this terminal. On the outer diameter of the magnetic circuit window, all turns must be laid sequentially one by one as shown in the figure.

After rewinding is completed, the winding must be impregnated with varnish to improve the insulating properties and to secure the wound wire in its place. Since you don’t need a lot of varnish here, you can use any varnish that is resistant to temperatures up to 105 o C. After impregnation with varnish, leave the autotransformer to dry for a couple of hours. For best effect, you can place it in a warm place. Leave the room where the work was carried out and it is very advisable to open the window for ventilation.

After drying, it is necessary to make a path for stress relief. This can be done using a knife or sanding paper. We make a path from the outer window to the inner one about 3 cm long (shown in the figure below).

Currently, many voltage regulators are produced and most of them are made using thyristors and triacs, which create a significant level of radio interference. The proposed regulator does not produce interference at all and can be used to power various AC devices, without any restrictions, unlike triac and thyristor regulators.
In the Soviet Union, a lot of autotransformers were produced, which were mainly used to increase the voltage in the home electrical network, when the voltage dropped very strongly in the evenings, and LATR (laboratory autotransformer) was the only salvation for people who wanted to watch TV. But the main thing about them is that at the output of this autotransformer the same correct sinusoid is obtained as at the input, regardless of the voltage. This property was actively used by radio amateurs.
LATR looks like this:

The voltage in this device is regulated by rolling a graphite roller along the exposed turns of the winding:

Interference in such a LATR was still due to sparking at the moment the roller rolled along the windings.
In the magazine “RADIO”, No. 11, 1999, on page 40, the article “Interference-free voltage regulator” was published.
Diagram of this regulator from the magazine:

The regulator proposed by the magazine does not distort the shape of the output signal, but the low efficiency and the inability to obtain increased voltage (above the mains voltage), as well as outdated components that are difficult to find today, negate all the advantages of this device.

Electronic LATR circuit diagram

I decided, if possible, to get rid of some of the disadvantages of the regulators listed above and preserve their main advantages.
Let’s take the principle of auto-transformation from LATR and apply it to a conventional transformer, thereby increasing the voltage above the network voltage. I liked the transformer from the uninterruptible power supply. Mainly because it doesn't need to be rewound. It has everything you need. Transformer brand: RT-625BN.

Here is his diagram:

As can be seen from the diagram, in addition to the main winding of 220 volts, it contains two more, made with a winding wire of the same diameter, and two secondary powerful ones. The secondary windings are excellent for powering the control circuit and operating the cooler for cooling the power transistor. We connect two additional windings in series with the primary winding. The photographs show how this was done by color.

We supply power to the red and black wires.

Voltage is added from the first winding.

Plus two windings. The total is 280 volts.
If you need more voltage, you can wind more wires until the transformer window is filled, after first removing the secondary windings. Just be sure to wind it in the same direction as the previous winding, and connect the end of the previous winding to the beginning of the next one. The turns of the winding should, as it were, continue the previous winding. If you wind it in the opposite direction, it will be a big nuisance when you turn on the load!
You can increase the voltage, as long as the regulating transistor can withstand this voltage. Transistors from imported TVs are found up to 1500 volts, so there is room.
You can take any other transformer that suits your power, remove the secondary windings and wind the wire to the voltage you need. In this case, the control voltage can be obtained from an additional auxiliary low-power transformer of 8 - 12 volts.

If someone wants to increase the efficiency of the regulator, then they can find a way out here. The transistor wastes electricity on heating when it has to greatly reduce the voltage. The more you need to reduce the voltage, the stronger the heating. When open, the heating is negligible.
If you change the circuit of the autotransformer and make on it many outputs of the voltage levels you need, then by switching the windings you can supply the transistor with a voltage close to the one you need at the moment. There are no restrictions on the number of transformer pins; you only need a switch corresponding to the number of pins.
In this case, the transistor will be needed only for minor accurate voltage adjustments and the efficiency of the regulator will increase and the heating of the transistor will decrease.

Production of LATR

You can begin assembling the regulator.
I modified the diagram from the magazine a little, and this is what happened:

With such a circuit, you can significantly increase the upper voltage threshold. With the addition of an automatic cooler, the risk of overheating of the control transistor has been reduced.
The case can be taken from an old computer power supply.

You immediately need to figure out the order of placement of the device blocks inside the case and provide for the possibility of their secure fastening.

If there is no fuse, then it is imperative to provide other short circuit protection.

The high-voltage terminal block is securely attached to the transformer.

I installed a socket at the output to connect the load and control the voltage. The voltmeter can be set to any other voltage, but not less than 300 Volts.

Will need

We will need details:

• Cooling radiator with cooler (any).
• Development board.
• Contact blocks.
• Parts can be selected based on availability and compliance with nominal parameters; I used what came to hand first, but chose more or less suitable ones.
• Diode bridges VD1 - 4 - 6A - 600 V. From the TV, it seems. Or assemble it from four separate diodes.
• VD2 - for 2 - 3 A - 700 V.
• T1 – C4460. I installed the transistor from an imported TV at 500V and a dissipation power of 55W. You can try any other similar high-voltage, powerful one.
• VD3 – diode 1N4007 1A 1000 V.
• C1 – 470mf x 25 V, it is better to increase the capacity even more.
• C2 – 100n.
• R1 – 1 kOhm potentiometer, any wirewound, from 500 Ohms and above.
• R2 – 910 - 2 W. Selection of transistor base current.
• R3 and R4 - 1 kOhm each.
• R5 – 5 kOhm substring resistor.
• NTC1 is a 10 kOhm thermistor.
• VT1 – any field-effect transistor. I installed RFP50N06.
• M – 12 V cooler.
• HL1 and HL2 are any signal LEDs; they do not need to be installed together with quenching resistors.

The first step is to prepare the board to house the circuit parts and secure it in place in the case.

We place the parts on the board and solder them.

When the circuit is assembled, it is time for its preliminary testing. But this must be done very carefully. All parts are under mains voltage.
To test the device, I soldered two 220 volt light bulbs in series so that they would not burn out when 280 volts were applied to them. There were no bulbs of the same power and therefore the filament of the spirals varied greatly. It must be borne in mind that without a load the regulator operates very incorrectly. The load in this device is part of the circuit. When you turn it on for the first time, it’s better to take care of your eyes (in case you messed something up).
Turn on the voltage and use a potentiometer to check the smoothness of the voltage adjustment, but not for long, to avoid overheating of the transistor.

A laboratory autotransformer, or LATR for short, is a device for changing the alternating current voltage of various electrical appliances. This device is a type of ordinary transformer. During the process of changing voltage using LATR, the frequency of the device at any stage remains the same. His work is based on the phenomenon of electromagnetic induction. The device includes many additional modifications.

Autotransformer device

There is one common winding located on the magnetic core of the LATR, and three additional terminals extend from it. Older autotransformer models have a current-collecting contact on the secondary winding, which allows:

• output voltage is smoothly adjustable;
• at one moment change one voltage value to another;
• change the heating intensity of the soldering iron tip;
• regulate electric lighting.

The most common type of autotransformer is a toroidal magnetic circuit. It is a ring-shaped core made of electrical steel.

Copper wire, or winding, is wound around the core. In addition, the design of the device has an additional tap - a tap from the winding. In total, there are exactly three contacts.

For large transformations, it is best not to use LATR. The reasons are as follows:

1. The chances of resulting in a short circuit are too high. Electronic circuits specially adapted for this purpose or additional resistance will help deal with the problem.
2. A conventional transformer is more suitable for many reasons, such as higher efficiency, lower steel costs, reduced dimensions and weight, and reduced tool costs.

Electronic device circuit

Buying a reliable LATR with the available assortment is not an easy task. There are too many low quality products on the market. As an option, you can purchase an industrial design, but the prices are quite high, and the dimensions are rather large. In this case, a more acceptable option would be to create an autotransformer with your own hands.

Materials required for assembly

The materials that will definitely be needed to assemble a homemade electronic LATR on a field-effect transistor are as follows:

• copper wire (winding);
• heat-resistant varnish;
• rag tape;
• magnetic circuit (both rod and toroidal types are suitable);
• a housing with fixed connectors to which power and load will be connected.

LATR winding calculation

First, you need to decide within what limits the LATR will operate on thyristors. The optimal network supply value is 220 V. The secondary voltage values ​​are 127, 180 and 250 V, respectively. The power with these parameters should not exceed 300 W. But you can determine these values ​​yourself, the main thing is that everything corresponds to each other.

Now you need to calculate the winding. It must be calculated based on the larger current. The highest current value can be obtained by converting a voltage of 200 V to 127 V. Under such conditions, the autotransformer becomes a step-down one. The maximum current that passes in the winding of both networks is calculated as follows:

I = I2 - I1 = P / U2 - P / U1 (I, I2, I3 - currents in the corresponding sections of the circuit, A, P - power, W, U1, U2 - voltages of the primary and secondary circuits, V).

Wire diameter d is calculated by the formula:

There is a special table according to which the type and cross-section of the wire is determined. They are selected taking into account the calculated current and the average current density for LATR, equal to 2 A/mm².

Formula for calculating the transformation ratio n:

Formula for calculating the design power Pp:

Pp = P * k * (1 - 1/n) (k is a coefficient taking into account the efficiency of the autotransformer)

W0 = m / S (W0 is the number of turns per 1 volt, m = 50 for rod and 35 for toroidal magnetic cores).

If the steel quality is insufficiently high, the W0 value increases by 20−30%. When calculating turns, it increases by 5−10%. In this way, voltage sags can be successfully avoided. To calculate the length of the wire, one turn is wound onto the magnetic core and its length is measured. The resulting value is multiplied by the maximum number of turns and 25-30 centimeters are added for each terminal to the terminal.

Connection diagram LATR 2m

First, we take the toroidal magnetic core, which was already mentioned above. The place where the winding will be applied is insulated with rag tape. We bring out the wire for the first power terminal (all subsequent wires are brought out without breaking). We fix the first turn on the magnetic circuit and wind the calculated amount. Upon reaching a turn that corresponds to the selected voltage value, a loop is drawn, then you must continue to wind the wire.

After drying, the autotransformer is placed in the housing. The first wire brought out is connected to the power connector. This connector must be electrically connected to the common load terminal, so it connects the wires to each other with some kind of conductor.

Connect the loop output for 220 V to the second power terminal. Connect the remaining wires to the corresponding terminals of the secondary circuit. There is a special autotransformer diagram that shows the wire terminals. You need to follow it when connecting wires to the terminals.

Next, add a housing to the autotransformer and make a mount for the regulator handle. Attach a slider with a carbon brush to the handle. You need to make sure that the brush touches the top of the winding tightly. The area over which the brush will move must be marked, and the insulation at the marking location must be removed. So, the brush will have direct electrical contact with the secondary winding. The secondary voltage terminals, in addition to the common one, are shaded with one connected to a carbon brush. When connected, the voltmeter is fixed.

Now you need to make sure that the autotransformer works as it should. To check the quality of the device, perform the following steps:

If no problems are found, then the laboratory autotransformer is completely ready for use.

Autotransformers (LATR) are used to smoothly regulate alternating current voltage in various works related to electrical engineering. They are most often used to change voltage in household appliances and construction.

An autotransformer is one of the types of transformers. The two windings in this device are directly connected to each other. As a result, two types of communication appear between them, one of which is electromagnetic and the other electrical. The coil has several terminals with different voltage output values. The difference from a conventional transformer is increased efficiency due to a partial change in power.

Design features

Transformers are electrical equipment with more than 2 or more windings, which have an inductive coupling that serves to change electrical energy by voltage.

There can be only one winding for an autotransformer, or several windings covered by a magnetic flux, wound on a core with ferromagnetic properties, for other transformers.

Today, 1-phase transformers (LATP) have gained popularity. This is a laboratory version of a transformer in which both windings are not isolated from each other, but have a direct connection, therefore, in addition to electromagnetic communication, they have an electrical connection. Such a common coil is equipped with several terminals. At their output you can get different voltages.

Operating principle

Due to their design features, autotransformers can produce both low and high voltage. The figure shows circuits of autotransformers with voltage reduction and increase.

If you connect an alternating current source to X and “a,” a magnetic flux is created. At this moment, a potential difference of the same value is induced in the turns of the coil. As a result, between X and “a” an EMF appears equal to the value of the EMF of the 1st turn multiplied by the number of turns of the winding located in the interval between these points.

When the consumer load is connected to the coil to terminals X and “a”, the secondary coil current will flow through the section of the winding between these points. Keeping in mind that the primary and secondary currents overlap each other, an insignificant current will flow between X and “a”.

Due to this feature of the operation of the autotransformer, the main part of the winding is made of wire of small cross-section, which reduces its cost. If it is necessary to change the voltage within small limits, then it is advisable to use such autotransformers (LATR).

Types of autotransformers

Several types of autotransformers have found application:

• VU-25 - B, serves to smooth out secondary currents in the protective circuits of transformers.
• ATD— power 25 watts, long-lasting, has an old design and is little used.
• LATR - 1, suitable for 127 volt applications.
• LATR - 2, used with a voltage of 220 volts.
• DATR - 1, serves for weak consumers.
• RNO- for heavy loads.
• ATCN used in measuring television devices.

Autotransformers are also divided by power:

• Low power, up to 1000 volts;
• Medium power, over 1000 volts;
• Power.

Laboratory autotransformers

This version is used in low voltage networks to regulate voltage in laboratories. Such single-phase LATRs are made of a ferromagnetic core in the form of a ring, on which one layer of insulated copper wire is wound.

In several places of the winding, conclusions are made in the form of branches. This makes it possible to use such devices as autotransformers with the ability to increase or decrease the voltage with a constant transformation ratio. On top of the winding there is a narrow path on which the insulation is cleaned. A roller or brush contact moves along it, allowing the secondary voltage to smoothly change.

Turn short circuits do not occur in such laboratory autotransformers, since the load and network current in the winding are directed towards each other and are close in value. LATR capacities range from 0.5 to 7.5 kVA.

Three-phase transformers

In addition to other design options, there are also three-phase versions of autotransformers. They have either three or two windings.

They are most often connected in the form of a star with a separate neutral point. A star connection makes it possible to reduce the voltage calculated for the insulation of the device. To reduce the voltage, power is supplied to terminals A, B, C, and the output is obtained at terminals a, b, c. To increase the voltage, everything is done the other way around. Such transformers are used to reduce the voltage level when starting powerful electric motors, as well as to regulate voltage in stages in electric furnaces.

High-voltage autotransformers are used in high-voltage network systems. The use of autotransformers optimizes the efficiency of energy systems, makes it possible to reduce the cost of energy transportation, but at the same time contributes to an increase in short circuit currents.

Operating modes

• Autotransformer.
• Combined.
• Transformer.

If the operating requirements of autotransformers are met, including compliance with oil temperature control, it can operate for a long time without overheating or breakdowns.

Advantages and disadvantages

The following advantages can be highlighted:

• The advantage is high efficiency, because only a small part of the transformer power is converted, and this is important when the output and input voltages differ by a small amount.
• Reduced consumption of copper in coils, as well as steel core.
• The reduced dimensions and weight of the autotransformer make it possible to create good transportation conditions to the installation site. If greater power of the transformer is required, then it can be manufactured within the permissible limitations of dimensions and weight for transportation by transport.
• Low cost.
• Smooth voltage removal from the movable current-collecting contact connected to the winding.

Disadvantages of autotransformers:

• Most often, the coils are connected with a star with a neutral, which is grounded. Connections according to other schemes are also possible, but their implementation causes inconvenience, as a result of which they are rarely used. The neutral must be grounded through a resistance or using a blind method. But we must not forget that the grounding resistance should not allow the potential difference across the phases to exceed the moment when any one phase is short-circuited to ground.
• The increased potential for overvoltage during a thunderstorm at the input of the autotransformer makes it necessary to install arresters that do not turn off when the line is turned off.
• Electrical circuits are not isolated from each other (primary and secondary).
• The dependence of low voltage on high voltage, as a result of which failures and surges of high voltage affect the stability of low voltage.
• Low leakage flux between primary and secondary windings.
• Insulation of both windings has to be done for high voltage, since there is an electrical connection between the windings.
• Autotransformers of 6-10 kilovolts cannot be used as power ones with the voltage reduced to 380 volts, because people have access to such equipment, and due to an accident, the voltage from the primary winding can get to the secondary winding.

Application

Autotransformers have a wide range of uses in various fields of human activity:

• In low-power devices for setting up, powering and testing industrial and household electrical equipment, automatic control devices, in laboratory conditions on benches (LATRs), in communication devices and devices, etc.
• Power versions of 3-phase autotransformers are used to reduce the starting current of electric motors.
• In the energy industry, powerful models of autotransformers are used to connect high-voltage networks with networks of similar voltages. The transformation ratio in such devices usually does not exceed 2 – 2.5. To change the voltage on an even larger scale, other devices are required, and the use of autotransformers becomes impractical.
• Metallurgy.
• Utilities.
• Production of equipment.
• Petroleum and chemical production.
• Educational institutions use LATRs to demonstrate experiments in physics and chemistry lessons.
• Voltage stabilizers.
• Auxiliary equipment for machines and recorders.

How to choose an autotransformer

First, determine where the autotransformer will be used. If for testing power equipment at an enterprise, then one model is needed, but for powering a car radio during repairs, then a completely different one.

• Power. It is necessary to calculate the load of all consumers. Their total power should not exceed the power of the autotransformer.
• Adjustment interval . This parameter depends on the action of the device, that is, to increase or decrease. Most often, devices are of the voltage-reducing type.
• Supply voltage . If you want to connect an autotransformer to your home network, then it is better to purchase a device for 220 volts, and if for a 3-phase network, then for 380 volts.

With such a device, you can change the network voltage values ​​and set the values ​​that are needed for a specific type of load.