Arc Welding Power Source

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Arc Welding Power Source

By: Nanaksharan Singh

Welding Technology

CBL


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Introduction

Welding is a process of joining two metals. To make ajoint of two metals immense heat is required. This

heat is created in the form of an electric arc. To create

this arc a Power Source is required

.An arc welding power source is designed to changehigh voltage low amperage current into a safe lowvoltage (between 50 and 100 volts) heavy currentsupply (even above 500 Amperes) suitable for arcwelding. Power source is required to supply thecurrent that supports the arc column for fusion

welding


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power sources can be divided into three main categories

AC Power Source

e.g. Transformers and Alternator

DC Power Source

e.g. generator and Rectifier

Combination AC & DC Power Source

e.g. AC transformers with DC rectifiers.


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AC- Power Source

A welding transformer changes high voltage, low

amperage power to low voltage, high amperagewelding power.


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For a Transformer, the significant

relationship between voltages and

current and the turns in the primary

and secondary winding are as follows:-

N1/N2= E1/E2 = I1/I2


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DC Power SourceThe This type of power source is operated from the mains supply.

transformer steps down the mains voltage to a suitable weldingvoltage,

The rectifier changes the alternating current into direct current.

Very often this type of machine can be switched to give eitheralternating or direct current as required.


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ELECTRIC MOTOR DRIVEN

GENERATOR

The d.c. generator is a rotating

machine which can be driven by

an electric motor, petrol or diesel

engine.

DEISEL ENGINE DRIVEN

The engine driven type is

generally used for site work.


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Inverter Power Source

An inverter power source is different from a

transformer-rectifier type in that inverter

rectifies ac line current, uses an inverter

circuit to produce high frequency ac,reduces that voltage with an ac transformer,

and rectifies that to obtain the required dc

output.

Changing the ac frequency to a much higherfrequency allows a greatly reduced size of

transformer & reduced transformer losses.


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Basic relationship that applies to all

transformers:

V=NAfK

Where:-The magnitude of voltage to be transformed (V) is proportional to the

no. of turns of wire on the transformer coil (N), the cross-sectional

area of the transformer core (A), the frequency of the AC Voltage to

be transformed (f) and various design constants (K)


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Duty Cycle

Fundamentally, the Duty Cycle is a ratio of the Load- On

Time allowed in a specified time interval time.

National Electrical Manufacturers Association (NEMA)

specifies duty cycle based on a test interval of 10

minutes in an ambient temp. of 400C.

A 60%NEMA duty cycle means that the power source

can deliver its rated output for 6 out of every 10

minutes without overheating


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Duty Cycle at other than rated outputs as

follows:-

Ta = (I/Ia)2 X T


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Volt-Ampere Characteristics

Types of Welding Power Source

Constant Current Power Source Constant Voltage Power Source


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Constant Current Power Source

A welding power source which will produce a relatively small

change in amperage despite changes in voltage caused by a

varying arc length. Used mostly for welding with coated

electrodes.


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Constant Voltage Power Source

A welding power source which will produce a relatively small change

in voltage when the amperage is changed substantially. Used mostly

for welding with solid or flux cored electrodes.


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Polarity

The term Polarity is used to describe the electrical

connection of the electrode in relation to the terminal of a

power source. With direct current (DC), when the

electrode is connected to the +Ve terminal, the polarity is

designated as a direct current electrode positive (DCEP).When electrode is connected to theVe terminal, the

polarity is designated as a direct current electrode

negative (DCEN).

When alternating current (AC) is used, the polarity changesevery half cycle of 50Hz


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DCEN (Straight Pol.) DCEP (Reverse Pol.)


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Safe practice and accident avoidance

Make Sure all insulation is tight & secure before turning on Power.

Dont touch electrically live parts with bare skin, Do Not work withwet gloves, shoes or clothing.

Welding leads and return leads should be insulated and thickenough to carry the current safely; connectors should also beinsulated to avoid inadvertent access to live conductors andadequate for the current being carried.

The welding return lead should be connected as near as practicableto the welding arc; metal rails, pipes and frames should not be usedas part of the welding circuit unless they are a part of the workpieceitself.

The welding leads, connection devices and electrode holder or torchshould be checked at regular intervals for 'fitness for use'; repair orreplace damaged or worn components.

Inspect frequently and immediately replace worn or damaged parts. Always disconnect power source before performing any

maintenance.

Recommended Welding Cable Size


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Recommended Welding Cable SizeTotal length of copper cable in weld Ckt.

AMPS 15 m 30m 45m 60m

100 16 mm2 25 mm2 25 mm2 25 mm2

150 25 mm2 25 mm2 25 mm2 35 mm2

200 35 mm2 35 mm2 35 mm2 50 mm2

250 50(mm)2 50 mm2 50 mm2 70 mm2

300 70 mm2 70 mm2 70 mm2 95 mm2

350 95 mm2 95 mm2 95 mm2 105 mm2

400 95(mm)2

95 mm2 95 mm2 105 mm2500 105 mm2 105 mm2 105 mm2 ------

Reference : WELSPRING UNIVERSAL

(Govt. Recognized Export House)

New Delhi (INDIA)


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Arc Welding Power Source