HOW DOES AC WELDING DIFFER FROM DC WELDING

[stuckmotor]

Thanks Shield Arc. I guess I was wrong.

 

[Shield Arc]

Thanks Shield Arc. I guess I was wrong.

You are welcome!
I've done it since I started out, at 14-years old.

 

[stuckmotor]

Shield Arc,
Would you do it with an AC welder? That's all I have.

 

[k0ua]

Well I'm no pro, but that's how I've been doing it for years.

And I know I am not a pro, and I hold the electrode to get started too.

 

[buickanddeere]

AC current starts and stops 120 times per second . DC is continuous .

 

[k0ua]

Shield Arc,
Would you do it with an AC welder? That's all I have.

Some things to keep in mind. When your skin is wet, your gloves soaked thru, be CAREFUL!. If you don't have to weld, consider doing it some other time. If you have to, try real hard not to "complete the circuit". In other words, don't touch both sides of circuit at the same time. Don't lean on that bush hog and touch the electrode at the same time. The OCV (Open Circuit Voltage) measured between ground and stinger is not supposed to be over 80 volts, but 80 volts is enough to knock your **** stiff if you are wet.

On a dry fall day you could touch both stinger and ground and probably never feel it, depending on how calloused your hands are. Of course if you just touch ground and never touch the stinger, no current will flow thru your body. Also if you just touch the stinger and not the ground clamp, or the weldment, then no current will flow thru your body either.

Welding is just like working around any other source of electricity, the thing that needs to be foremost in your mind is "don't become part of the circuit". When I touch an electrode to steady it when striking the arc, I make it a point to not be touching the grounded workpiece. I also make it a point to not have wet gloves or wet skin. Dry calloused skin has a high resistance to the flow of current, but wet skin has a very low resistance to the flow of current.

Also keep in mind that a welders source of current is not very current limited from the point of view of the human tolerance to current flowing across the body. They tell us that at as little as 50 milliamps is enough to kill you. That is 50 thousandths of 1 amp. We often set our welder to deliver over 100 amps. That is thousands of times more than what is needed to kill us.

 

[Soundguy]

lol, I think our terminology is getting confused, caps don't fill holes ( as in a zero volt reference and up ) they smooth out " ripples"/"noise" of a specific voltage and are also used as storage cells. .

Your the confused one!

what you are calling filling a hole, as in the space between the crests of the positive wave form as compaired to steady state dc.. and YES, caps will smooth / filter that bumpy DC to steady state DC .

 

[Soundguy]

lol, I think our terminology is getting confused, caps don't fill holes ( as in a zero volt reference and up ) they smooth out " ripples"/"noise" of a specific voltage and are also used as storage cells. .

here, this might help. and for the other EE's out there, this drawing is OBVIOUSLY not scaled.. freq, etc, waveform errors, etc. it's just a pictogram.

Skyhook... the first line shows half wave dc, an ac wave form ran thru a diode and it chops one half off as the diode oposes current flow in one direction.

the next line shows full wave dc, either a transformer and 2 diodes, or 4 diodes aranges so that the lower waveform is tossed 'up top'.. this makes for a riple-dc.

Now, if you take a capacitor and put across the ground reference and the positive test point. the capacitor will 'fill in' the space between those waveforms. ( of course you must have a large enough cap to filter with... loaded or unloaded circuit will effect that, yada yada..

the third line shows the full wave dc with a steady state line over it and a green hash shaded area.. that's what the cap is doing, the green shaded area.

to your vom, the 4 line is what gets reported... steady state dc.

 

[k0ua]

View attachment 456660


here, this might help. and for the other EE's out there, this drawing is OBVIOUSLY not scaled.. freq, etc, waveform errors, etc. it's just a pictogram.

Skyhook... the first line shows half wave dc, an ac wave form ran thru a diode and it chops one half off as the diode oposes current flow in one direction.

the next line shows full wave dc, either a transformer and 2 diodes, or 4 diodes aranges so that the lower waveform is tossed 'up top'.. this makes for a riple-dc.

Now, if you take a capacitor and put across the ground reference and the positive test point. the capacitor will 'fill in' the space between those waveforms. ( of course you must have a large enough cap to filter with... loaded or unloaded circuit will effect that, yada yada..

the third line shows the full wave dc with a steady state line over it and a green hash shaded area.. that's what the cap is doing, the green shaded area.

to your vom, the 4 line is what gets reported... steady state dc.

I considered doing this drawing, but I was lazy. I am glad you posted it.

 

[Soundguy]

I considered doing this drawing, but I was lazy. I am glad you posted it.

I realize it's hard for those that are not engineers or tech's to visualize some of these concepts, and how cap's and inductors interact with circuits voltage and current, etc.

hopefully the drawing will help. it's a bad drawing, but i think it will work. the signal 'generator' ( my hand ) needs to be calibrated.