Snap-On TIG 250 AC-DC, Service Manual

Page: 4 / 37

CEBORA S.p.A.
4
2 - SYSTEM DESCRIPTION
2.1 - Introduction.
The TIG 250 AC/DC is un electronic power source suitable for AC/DC TIG welding with
high-frequency arc striking.
It may be used together with a range of accessories for various types of applications (see list
in the Sales catalogue).
The operator interface is developed via the control panel built into the power source.
2.2 - Technical specifications.
To check the technical specifications, see the plates affixed to the equipment, the Instruction
Manual, and the Sales Catalogue.
2.3 - Description of TIG 250 AC/DC power source.
The TIG 250 AC/DC is a controlled-current power source, made up of a single-phase
transformer and a converter that can be configured as a rectifier bridge for direct current
applications, or as a static switch for alternating current applications.
The configuration may be selected using the AC/DC selector switch (30)(AF) on the front
panel.
Referring to the electrical diagram in par. 5.1, drawing 4.1 and table 4.2, one may identify the
main blocks that make up the power source.
The main switch (15), on the rear panel, directly powers the transformer (46) and the terminal
board (52), to which are connected the various internal services of the power source.
The power source can operate with either mains at 208 Vac or at 230 Vac, depending on the
setting of switch (15). As an effect of the primary circuit of the transformer (46) which acts as an
autotransformer, the terminal board (52) and thus all internal services connected to it are always
powered at 230 Vac.
The mains filter board (51), connected to the terminal board (52), contains the filter to reduce
conducted interference reflected in the mains.
The transformer (46) has a second power winding, with voltage and current values suitable for
welding, and two secondary service circuits; all windings are made up of two half-windings
arranged on the two columns of the magnetic core.
One 30 Vac service winding powers the circuits for the signals that dialogue outside the
power source through the connector board (49).
The second service winding a 27 Vac powers the thermal protection circuits of the power
source (thermostats on inductor (50) and transformer (46)) and to measure the pressure of the
liquid in the cooling unit.
The secondary power circuit of the transformer (46) is connected to the current converter,
made up of the thyristor group (47) (SCR1 and SCR2), the diode module (19) (D1, D2, D3), the
inductor (50) and the AC/DC selector switch (30). The electrical diagram of the power source in
par. 5.1 shows the operating table of the AC/DC selector switch (30).
Based on the position of the AC/DC selector switch (30), the converter acts as a Half-
controlled rectifier to generate and regulate direct current, or as static switch to generate and
regulate alternating current (in the latter instance the frequency of the alternating output current
corresponds to the supply voltage frequency of the power source).
The SCR1 and SCR2 (47) receive the driver signals from the control board (40), through the
shut-off board (48), and the output current is regulated by the control board (40) by changing the
firing angle of SCR1 and SCR2 (47).
3.302.221 15/01/07