Adjustable transformer based on LATR. Scheme, description

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Adjustable transformer based on LATR. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Regulators of current, voltage, power

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There are many LATRs 220 V 9 A in operation. Over time, the moving contact mechanism wears out, as a result of which the LATR fails. On the basis of a faulty LATR, a transformer with switched windings was made, which not only completely replaces the LATR, but also provides galvanic isolation between the input and output, and also provides a maximum output voltage of up to 465 V.

Main Specifications

Rated input voltage, V .................220
Output voltage, V......1...465
output adjustment step
voltage, V .................1
Maximum output current, A, at output voltage
1...45 V ...................20
46...85 V ...................20
86...165 V .................10
166...265 V .................6
266...465 V .................3
Dimensions, mm .......... 200x170x280

The schematic diagram of the device is shown in the figure.

Adjustable transformer based on LATR
Fig. 1

Its basis is the T1 transformer; primary (network) winding I - the original LATR winding containing 220 turns. Secondary windings II-XI are wound on top of it. The output voltage is set by switches SA2-SA11. They switch the windings of the K1-K10 relay, the contacts of which, in turn, connect the corresponding series-connected output windings to the output. The relay windings are powered by a rectifier on a diode bridge VD1-VD4. The inclusion of the device in the network and the presence of voltage in it is signaled by the LED HL1.

The T1 transformer is mounted on a duralumin plate 200x280x5 mm. The secondary windings II-XI are wound with PEV-2 wire at the rate of 1 turn per volt at a maximum current density of 6 A/mm2. Secondary winding wire diameter: XI - 0,8 mm, X - 1,18 mm, IX - 1,5 mm, VIII - 2,12 mm, the rest - 2,5 mm. The secondary windings are insulated from the primary with two layers of cotton tape. The secondary windings are not isolated from each other, since the breakdown voltage of the PEV-2 wire insulation exceeds 1,5 kV. To increase the electrical and mechanical strength, the windings are impregnated with BF-2 glue. Relays K1-K10 - automotive 90.3747 with contacts for a maximum current of 30 A Due to the inertia of the relay, the ripple of the supply voltage does not affect their operation. In the case of using other types of relays, it may be necessary to connect a smoothing capacitor to the output of the diode bridge VD1 - VD4, the capacitance of which is selected experimentally. Toggle switches SA2-SA11 - TP1-2. The installation of the power section is made with a wire with a cross section of 6 mm2.

Establishing the device consists in checking the phasing of the secondary windings. An AC voltmeter is connected to the output of the device. Before the first connection to the network, it is necessary to turn off the toggle switches SA2-SA11. After turning on the network, the HL1 indicator should start to glow.

Turn on the SA11 toggle switch and make sure that the output voltage is 1 V. Turning on the SA11, SA10 toggle switches, etc. should cause an increase in the output voltage. If, when a toggle switch is turned on, the voltage decreases, then this indicates an incorrect phasing of the corresponding winding. In this case, it is necessary to swap the connection of its conclusions. Turning on all the toggle switches, make sure that there is an output voltage of 465 V. This completes the adjustment. The specified voltages correspond to the rated mains voltage of 220 V. If it differs from the nominal, it should be noted that all output voltages and its regulation step are proportional to the mains voltage.

Automotive relay contacts are not designed for high voltage switching.

If the output voltage exceeds 45 V, then to ensure the safety of the contacts, it is necessary to avoid switching them when the load is connected.

The proposed device is recommended to be connected to the network without load, set the required output voltage and only then connect the load.

Shutdown is performed in the reverse order: first, the load is turned off, then the device.

Author: K. Moroz, Nadym, YNAO; Publication: radioradar.net

See other articles Section Regulators of current, voltage, power.

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