LHF 630 & 800 file 0740 800 028

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Welding Service Manual

Transcript of LHF 630 & 800 file 0740 800 028

  • 0740 800 028 Valid from machine no. 701--xxx--xxx9208--1

    LHF 630/800

    Service manual

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    LIST OF CONTENTS PageRATING PLATE 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DESCRIPTION OF OPERATION OF LHF 630/800 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .BLOCK DIAGRAM, LHF 630/800 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .COMPONENT DESCRIPTION, CIRCUIT DIAGRAM 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .CIRCUIT DIAGRAM, LHF 630/800 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DESCRIPTION OF OPERATION, CIRCUIT BOARD K70 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .CIRCUIT DIAGRAM, CIRCUIT BOARD K70 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .COMPONENT POSITIONS, CIRCUIT BOARD K70 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .REPLACEMENT OF THYRISTORS 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    Note that only the English part of the instruction manual has been included.

    INSTRUCTION MANUAL 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .PRESENTATION 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INSTALLATION 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .TECHNICAL DESCRIPTION 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .TECHNICAL DATA 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .MAINTENANCE 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .STATIC CHARACTERISTICS 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .EFFICIENCY AND POWER FACTOR 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .SPARE PARTS LIST 27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    This service manual is valid from machine no 701--XXX--XXX.

    The date on the front page is followed by a one (9208 --1), this means that the layout has beenaltered, the contents are still the same as in 9208 though.

    Rights reserved to alter specifications without notice.

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    RATING PLATE

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    1. The symbols indicate that the LHF 630 incorporates a transformer and a rectifier.

    2. Current/voltage characteristic for MMA welding.

    3. Indicates that the unit is intended for connection to a 3--phase supply at 50 or 60 Hz.

    4. The machines serial number, consisting of three groups of figures (xxx yyy vzzz).

    The first group (xxx) indicates the version. The numerals indicate the year and week ofapproval of the design version.

    The second group (yyy) indicates the year and week of the machines final testing:e.g. 203 indicates 1992, week 3.

    The final (vzzz) group consists of three or four numerals and is a consecutive serialnumber from 0001 to 9999.

    5. These letter and numeral combinations indicate that ESAB complies with existing nation-al and international standards.

    6. X = Intermittance factor: indicates for how long welding can be carried out at thespecified welding data, expressed as a percentage of a 5--minute period.

    I2 = Current at the respective intermittance factor.U2= Arc voltage.Uo= No--load (open--circuit) voltage.

    7. Supply voltages and primary current at various intermittance factors.

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    DESCRIPTION OF OPERATION OF LHF 630/800

    GENERAL DESCRIPTION

    The LHF 630/800 are thyristor--controlled welding power sources incorporating mainsvoltage compensation and intended for MMA welding, TIG welding and air--arc gouging.The mains voltage compensation ensures that the arc voltage and welding current remainstable even though supply voltage may vary. Electronic control ensures that the weldingcurrent maintains its set value at all times. A single knob regulates the welding current overits entire range.

    The following description refers to the block diagram on page 7.

    1 Reference potentiometer K57 for adjusting the welding current. The current settingis as defined by the ISO line.

    2 Reference potentiometer, connected to remote control socket K24, for remoteadjustment of the welding current.

    3,4,5 Galvanically isolated remote control device.The remote control circuit employs a double--winding transformer (K52),associated rectifier and voltage stabilisation circuit, A/D converter, optocouplerand D/A converter.A pulsed voltage transfers the reference voltage from the remote control terminalsocket via the optocoupler to the D/A converter, the output of which is an analogreference voltage.

    6 Selector switch K33 selects local or remote control of the reference voltage.The actual switching of the voltage reference signals is effected by analogswitches: the block diagram shows the switching only schematically.

    7 Current reference boost in response to short circuits.

    8 Reference voltage input from the local and external potentiometers respectively.

    9 This circuit boosts the welding current in the event of an arc short circuit, thuspreventing the electrode from burning on to the work during welding. The currentreference signal is increased electronically via 7) and 20).

    10 Assists striking of the arc by means of an elevated current reference signal duringstarting. See 14), Hot start.

    11 Reduces the welding current in the event of a long--duration short circuit, i.e. if theelectrode has burnt on to the workpiece. See 13), Foldback.

    12 Input for current signal from elevated shunt voltage.

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    13 Foldback.This is a timer circuit that starts when the arc is short--circuited. It reduces thewelding current via 11) if the short circuit persists, i.e. if the electrode has burnt onto the workpiece. This helps to protect the thyristors against abnormally highand/or long--duration short circuits.The foldback feature operates only in the MMA welding mode.

    14 Elevated starting current (starting boost, hot start)The starting current circuit briefly increases the welding current when starting toweld. The peak value of the starting pulse is about twice the set value of weldingcurrent, and gives the power source good starting characteristics during MMAwelding.Switch K79 (see 22), below) disconnects the feature during TIG welding.

    15 Power supply unit for the electronic equipment, supplying stabilised DC at 15 V.The neutral of the electronic circuitry is connected to the positive of the weldingvoltage (+ on K13).The power supply unit receives a three--phase alternating voltage from thesynchronising windings K1s3.

    16 Control comparator/amplifier, which compares the voltage signals from 8--12) andthen amplifies the summing voltage to provide a suitable control voltage signal tothe trigger unit 17). The good dynamic welding performance of the LHF 630/800is partly due to the characteristics of the amplifier.The no--load detector 21) reduces the amplifier output signal when there is no arc.

    17 Trigger unitThe trigger unit consists of three identical circuits (one for each phase). Eachcircuit provides trigger pulses for its thyristors, with phase angles in proportion tothe output voltage from the control amplifier. Auxiliary windings on the maintransformer provide synchronising signals.

    18 Thermal overload cutout, which interrupts the pulses to the thyristors in the eventof high temperature of the thyristor cooling fins.

    19 Shunt amplifier, amplifying the signal from the current shunt to a suitable level forinput to 12).

    20 Short--circuit detector, sensing short circuits of the arc. See also 13).

    21 No--load detector, senses no--load (open--circuit) voltage. See also 14) and 16).

    22 Switch K79 (MMA/TIG), switching the control characteristics between MMA andTIG. When the switch is in the TIG position, the elevated starting current andfoldback circuits are disconnected: if this were not done, there would beconsiderable risk of burning through the workpiece.Switching is effected electronically: the block diagram shows only a schematicrepresentation.

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    23 Control amplifier for air--arc gouging, producing a DC voltage that is proportionalto the reference voltage signal from 6), to give a constant--voltage characteristic.

    The shunt signal from 19) is used to provide a current limit that protects variousparts of the system, including the thyristor rectifier 26).

    24 Changeover switch for air--arc gouging, in the form of a three--position switch onthe front panel, which also controls selection of MMA and TIG welding.(See 22).)

    25 Main transformer (three--phase).

    26 Thyristor rectifier.

    27 Basic current resistor, 8.6 5%.

    28 Basic current rectifier.

    29 Freewheel diode.

    30 Shunt for measurement of welding current.

    31 Inductor for smoothing welding current.

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    BLOCK DIAGRAM, LHF 630/800

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    COMPONENT DESCRIPTION, CIRCUIT DIAGRAM

    K1 Main transformer

    K2.1 Main thyristors

    K2.2 Main diodes

    K2.3 Basic current diodes

    K2.4 Freewheel diode

    K6 Mains switch