Providing Power Supply for Arc Welders by Using Rectifier (Final)

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    Vahid Nahani

    Muhammad Firdaus

    Venothkumar

    Theivinderan Reddy

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    Rectification the process of converting an alternating voltage or alternatingcurrent into direct voltage or direct current

    2 types of rectifier

    Constant Current

    Constant Voltage

    Welding power supply - device that provides an electric current to perform welding

    Welding requires above 12000 amps which will take AC power from the utility

    mains and convert it to DC for the welder.

    Example :

    Car battery

    Sophisticated

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    Welding machines - a constant current (CC) or constant

    voltage(CV).

    Output Voltage - maintain steady current while constant voltage

    machine will fluctuate its output current to maintain a set voltage.

    Shielded metal arc welding will use a constant current source and

    gas metal arc welding and flux-cored arc welding typically use

    constant voltage sources.

    Constant voltage it also possible with a voltage sensing wire feeder.

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    Transformer is used to for

    the welding power supplyconverts the high voltage

    and low current electricity

    from the utility (AC) mains

    into a high current and

    low voltage , typically

    between 17 to 45 volts and55 to 590 amps

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    Primary side of transformer is connected to AC and

    the secondary part is connected to full wave diode

    rectifier and the output is dc power supply for

    welding.

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    Sometimes referred as metal inert gas (MIG).

    Semi-automatic or automatic arc welding process.

    Uses constant voltage supply

    Thus, change in arc length results in a large change

    in heat input and current.

    A constant voltage, direct current power source is

    most commonly used with GMAW

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    MIG arc welding power source has a secondary

    tapped transformer.

    It consists of a transformer, rectifier and output

    capacitor The step down transformer winding in primary and

    secondary side are separated, which means the

    output of transformer is isolated from the power

    line ground. The rectifier is a full wave bridge of silicon diodes

    output filter smoothest the secondary voltage to

    give a more consist weld.

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    switch is used to select step on the transformer

    mechanically can control the secondary output voltage

    rebus and reliable design

    the output voltage cannot be controlled remotely and

    input voltage fluctuations will affect the output.

    The output filter capacitor is sized on the basis

    permissible output ripple voltage

    the capacitor supplies the maximum output current I

    continuously and it charges up to the output voltage

    every 1/100 s for the full wave rectifier with 50Hz line

    frequency.

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    A bleeder resistor is connected across the output

    capacitor to discharge it when the supply is turned off

    and to remove the hazard of an unexpected voltage

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    overcome the effect of input fluctuations on the output

    The welding power source opposite maintains a constant

    output voltage using an SCR control circuit.

    rectifier that remains in non-conductive state, even

    when forward voltage is applied from anode to cathode,until a positive triggle pulse is applied to the gate and

    the SCR fires.

    rectifier that remains in non-conductive state, even

    when forward voltage is applied from anode to cathode,until a positive triggle pulse is applied to the gate and

    the SCR fires.

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    Two SCRs in this design are connected in anti-parallel at

    the input to the transformer primary allowing power tobe controlled during each half cycle of the AC input.

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    requires fewer moving parts and it can be remotelycontrolled and voltage fluctuations at the input do not

    affect the weld output.

    poor efficiency and low speed of control.

    If the dV/dt is too large , the device will begin to conductwithout a gate signal an will result in erratic circuit

    operation and potential device damage.

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    Since the advent of high-power semiconductors

    such as the insulated gate bipolar transistor(IGBT)

    it is now possible to build a switching power supply

    capable of coping with the high loads of arcwelding.

    These designs are known as inverter welding units

    first rectify the utility AC power to DC; then they

    switch (invert) the DC power into a step downtransformer to produce the desired welding

    voltage or current

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    The input power AC is rectified to DC using a power

    factor correction boost converter

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    A full bridge MOSFET power stage convert thevoltage back to AC at high frequency typically 50Hzto 100Hz.

    The transformer steps down the voltage which isthen rectified and smoothed at the output stage.

    high power conversion efficiency

    due to high frequency operation of the MOSFET

    bridge the size of the components can be greatlyreduced specially the transformer and the outputfilter stage.

    component size is inversely proportional to theoperating frequency

    invertor power source maintains a constant outputvoltage regardless of changes in line input voltageand output current

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    Advantages

    The main power transformer, which operates at 20,000Hertz

    is vastly more efficient than 60Hertz transformers, which

    means it can be much smaller and the huge advantage in

    weight and portability in favor of the inverter based arc

    welder machines

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    Advantages

    There is another advantage of the inverter power supplies -

    power cost. The inverter equipment is much more efficient

    than transformer equipment.

    The other significant advantage of inverter power supplies

    is that, by chopping up the incoming AC so finely, we end up

    with a very steady DC, without the typical 60 Hertz ripple.

    This results in a much smoother, more stable DC welding

    arc.

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    Thank You