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8/6/2019 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