ac Arc welding hazards

Discussion in 'General Electronics Chat' started by vinodquilon, Oct 31, 2010.

  1. vinodquilon

    vinodquilon Thread Starter Member

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    I know, for ac arc welding ground terminal of transformer should connect to work piece and electrode should be with positive terminal.

    For the initial arc formation there should be direct contact between both positive and negative terminals.

    My doubt is that, why this will not create any short circuit problems as of high amperage with low voltage situation ?

    Does it cause any serious injury if we touch the work piece at the time of welding as of high amperage with low voltage situation ?
  2. jpanhalt

    jpanhalt E-book Developer

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    It can kill you. Is that serious enough?

    There are numerous case reports of welders getting electrocuted by what they thought (prior to being killed) was an innocuous voltage. Remember, being dressed up for welding can make you very sweaty, which reduces your skin resistance.

    John
  3. Jaguarjoe

    Jaguarjoe Active Member

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    With AC welding, or anything AC, there are no positive and negative terminals because the polarities are constantly switching 50 or 60 times/second.

    Open circuit voltage on an arc welder could be around 80 volts or so and would probably bite you if you grabbed it.

    Voltage while actual welding could be around 30 volts or so. Based on personal experience, I've never felt a tingle from 30 volts AC or DC.

    The fraction of a second that the stick is in contact with the work should not cause any concern about short circuits.

    You can become an expert in one afternoon right here:

    http://www.esabna.com/euweb/awtc/Lesson1_1.htm
  4. Rbeckett

    Rbeckett Member

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    As a former welder by trade I can definately warn you that placing yourself in the welding circuit is a way bad idea. Also failure to properly connect the ground when using High Frequency arc starts is a bad thing and usually results in about a 6K volts jolt which causes pain in the joints in addition to potentially killing you. If you deide to learn to weld, you need to fully understand the equipment and it's proper use as well as wear and use all safety equipment every time you weld. That "it's just a quick bead" is usually the one that kills you. OSHA has recently begun looking at alternatives to welding and making the safety requirement even more stringent to reduce job site accidents. Welding also produces noxious fumes that result in all kinds of respiratory difficulties and cancer and that has resulted in mandated ventilation on job sites and in shops. Welding is a tough job, and it's getting tougher every day to find a qualified individual with the skills willingness, and ability to follow the new mandates. Stick with electronis, trust me it's a way better job in the long run.
    Bob
  5. DonQ

    DonQ Active Member

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    Short is a relative word. 10 ohms would count as a short for some low current devices, but even 1 ohm (or lower) is easy for a welder.

    When you touch to draw a spark, the resistance is very small for a moment. The current is high enough to usually form a spark at the tip of the rod. This immediately melts back the rod and the arc that forms has a relatively high resistance (only about an ohm or less, but at 50-100 or more amps, this is plenty). At this resistance, almost all of the energy of the welder is developed across the arc.

    When the rod sticks, the rod first melts, then rehardens (generally because you stabbed too quickly instead of 'scratching'). Then, the resistance is much lower and stays that way. At this point, the welding transformer may have, for example, 1/10 ohm, the welding wires 1/10 ohm and the welding rod and stuck tip another 1/10 ohm. With this, the power of the welder is shared between the transformer, wires and rod. After a little time, the transformer might begin to smoke, maybe the wires too. Usually, if this is too little resistance for the welder, some current sense device, either in the welder or on the wall (breakers) would shut it down. But the temperature inertia of the components, along with the time delay of the over-current shut-down, gives you time to twist the rod off and try again.

    Important: At no time was there ever a zero-ohm 'short'. At high currents, a few tenths of an ohm counts as a circuit. Maybe too much to maintain for very long, but it was never zero-ohms.
  6. DonQ

    DonQ Active Member

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    That's true, but AC/DC welders are fairly common, like mine. So even while AC welding with one of these, the terminals on the welder share the labels of AC and DC.

    Way back, I worked on a ocean-going ship with 32VDC battery systems. Barefoot (in the tropics), soaking in sweat, 32VDC lit me up! I don't suppose anyone will be welding in this condition (oops, I forgot another story... some other time), but I always put the 'ouch' limit something below 32VDC after that.
  7. vinodquilon

    vinodquilon Thread Starter Member

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    This is our very very old(but still using without any protective clothing !!!)
    typical Indian arc welding machine.

    [​IMG]

    [​IMG]
  8. jpanhalt

    jpanhalt E-book Developer

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    I don't know if that picture is intended as a joke. If not, "should" is perhaps a bit optimistic. "Might" might be a better choice. :D

    John
  9. vinodquilon

    vinodquilon Thread Starter Member

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    as shown below,in every ac welding transformer there will be separate outs
    for both Earth & Electrode holder.

    Why there is such a restriction exists- as we can interchange ac transformer secondary points as we
    desired ?

    [​IMG]
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