Refinement of the welding transformer TDE-101U2. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The TDE-101U2 transformer produced by the industry (hereinafter referred to as the apparatus) is easy to use, has small dimensions and weight. The device works well with electrodes with a diameter of 2-3 mm.

Along with these advantages, it also has a number of disadvantages, namely: the absence of a mains power switch, and most importantly, the PN mode of the device is only 20% [1]. If the PN is exceeded, the device begins to overheat and may fail. This limits the operating conditions of the device.

With the proposed revision, the device has been operating for more than 4 years. An analysis of the reasons for the unsatisfactory operation of the device showed that the main reason for the small PV mode is overheating of the windings and iron core. To eliminate this shortcoming, a fan of the VN-2 or VVF-71m type is mounted on metal racks in the lower part of the apparatus, working for air injection. Thus, forced cooling of the core and windings of the transformer is performed. The fan is fixed on four metal racks with M3 or M4 screws (Fig. 1).

(click to enlarge)

Connect the fan in parallel with the transformer (Fig. 2).

(click to enlarge)

On the top cover in a free place, an automatic switch of the AE1031-2UHL-25 A type is installed, which turns on the device and provides current protection. The transformer windings are wound with wire (1-2, 3-4) and busbar (7-8, 9-10) of the PDSK type. The critical temperature for this wire is over 130°C. The device has a thermostat circuit, described in [2] with modifications. The circuit allows you to control the temperature of the windings, iron core of the device, radiators of power thyristors from +30 to +80 ° C, set the heating temperature of the device, protecting it from overheating.

The scheme of the improved device is shown in Fig.3.

(click to enlarge)

The temperature sensors in the circuit are transistors VT2, VT3, VT4. A threshold device is assembled on transistors VT2 - VT5, which operates at a certain temperature of the cases of transistors VT2, VT3, VT4 due to an increase in the collector current of the transistor at an elevated case temperature. Due to the presence of positive feedback through the resistor R24, the process of opening transistors proceeds like an avalanche.

In this case, relay K1 is activated, with its contacts it turns off the power of relay K2, de-energizing the welding transformer.

When the temperature drops to the set value, the device automatically returns to its original state, including the welding transformer. The response threshold is regulated by resistor R17 within +30...+80°C.

Details. Transistors VT2, VT3, VT4 type MP39 - MP42, VT5 - type KT503, KT815. Relay K1 - type RES8, RS4.590.063, RES9 or any similar. It is important that it works stably at a voltage of 6 V, and the switching current and voltage are 0,05 A and 220 V. Relay K2 is of the RP-21-UHL 45 type or similar with the corresponding switching current. LEDs H1 - red type AL336A, B, K, H2 - green type AL336V, G, I. Transformer T4 - small-sized with an output voltage of 12-15 V, providing a current of up to 500 mA.

The device is assembled on a fiberglass board (board dimensions depend on the types of relays used) and mounted on racks under the top case cover. Transformer T4 is installed in a free space inside the housing. LEDs H1 and H2, resistor R17 are brought to the top cover of the device. LED H2 - power-on indicator, H1 - overheating indicator. Chip DA1 should be installed on a radiator with an area of ​​10 cm2. Transistor VT2 is glued with a "hat" through a gasket made of fiberglass or mica to the winding of the welding transformer, VT3 - to the iron core, VT4 - to the radiator of the power thyristor VS1 or VS3.

In this case, it is necessary to pay attention to the minimum thickness of the dielectric spacer and ensure reliable electrical insulation between the transistor case and the temperature control point. The installation of transistors, resistors, LEDs is carried out with the MGTF-0,15 wire, the installation of the T3 supply transformer is carried out with the MGSHV0,35 wire. Relay contacts K2 are connected in parallel and connected to the welding transformer with a MGShV wire with a cross-sectional area of ​​​​1,5-2 mm2. A properly assembled circuit starts working immediately. Resistors R16 and R18 set the limits for regulating the heating temperature of the device, heating the "hat" of the transistor VT2 with a household hair dryer, and control the thresholds for operation with a thermometer. Then the temperature sensors are glued and the operation of the circuit is checked. At the upper temperature control limit of +80°C at an ambient temperature of +25°C, the device should be switched off after burning 10-15 electrodes with a diameter of 2 mm. Turn on the machine after 7-10 minutes (this depends on the speed of welding or cutting, the type of electrode, the mains voltage (190-225 V).

References:

1. Transformer for arc welding TDE-101U2. Technical description and operating instructions.
2. Handbook of circuitry for a radio amateur / Under the editorship of V.P. Borovsky. -K.: Tehnika, 1987.

Author: A.Tatarenko

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