HOW DOES AC WELDING DIFFER FROM DC WELDING

[skyhook]

I thing i read somewhere that it does this 60 times a second and the DC if IIRC is like 60,000 but not sure probably need to look on that

Yes, 60 times a second ( thats where you get 60hz ), DC is a steady voltage.

 

[Renze]

Here's my understanding ( and I could be wrong ), AC goes from a negative value to a positive value, doing so, it crosses the "zero value" line, making poorer welds than a DC welder which has a "steady" value of current. Expert welders compensate for this constant change in voltage/current drop on AC. Personally, I use my machine on DC only, I like the welds better.

AFAIK all standard industrial welders are DC. The smoothness of the welder depends on its AC to DC converting ability, if you just use a converter to transform the AC sinus into DC, it still jumps from max to zero, just with bumps instead of into the negative current. WElding machines use capacitators to store the energy of the AC bump to release it in the hole, to smoothen the sinus washboard.

For that reason, three phase welders are usually the better welders, as they have three overlapping phases filling each others current dips. Then the capacitators have a much easier job, and are able to get a much more constant welding current.


However, for welding aluminium you need AC. Its because the oxide skin on aluminium has a higher melting point than the pure aluminium underneath. Just try to heat aluminium with a torch, you won t get a melting bath like you get with steel: you dont see anything happening, untill the oxide skin breaks and a big two inch hole drops in the aluminium sheet you were trying to heat.

To weld aluminium you need AC because it blasts through the oxide skin with short AC blasts, without heating the entire workpiece to melting point which will blow large holes in it.

Last friday i tossed a purlin cleat 5 yards down from a ladder, because the MMA inverter welder i borrowed from work, tickled me. Missed a friends head by a foot. Lately i get some tickles from my 350A mig, but not as often as i remember from the good (poor) old days of stick welding.

Boy, when i got a MIG i sometimes used the stick welder for dirty steel or awkward positions. But now, first time stick welding in 5 or 8 years, i dont miss it a second.

 

[skyhook]

From my understanding, from Lincoln Electric,, The output is at a consistent current level all the time on DC. The OP can read some info here. It is also my understanding that "capacitors" are used to "filter" or smooth out voltage, not fill in the holes of a sine wave, rectifier's/diodes are used for this purpose.

DC vs. AC Polarity for SMAW

 

[Oldtink]

From my understanding, from Lincoln Electric,, The output is at a consistent current level all the time on DC. The OP can read some info here. It is also my understanding that "capacitors" are used to "filter" or smooth out voltage, not fill in the holes of a sine wave, rectifier's/diodes are used for this purpose.

DC vs. AC Polarity for SMAW

Correct. Capacitors oppose a change in voltage. Coils, chokes and inductors oppose a change in current. Both are used in a power supply derived from an AC source to produce a smooth constant DC supply of voltage and current.

 

[Soundguy]

It is also my understanding that "capacitors" are used to "filter" or smooth out voltage, not fill in the holes of a sine wave,

Filtering, smoothing,a nd filling the holes , for the purposes of capacitors and filtering rectified ac to dc, they are one in the same. filling the hole is the 'smoothing' ...

rectifier's/diodes are used for this purpose.

No.. diodes are used to convert the ac to dc. in simple terms, a single diode in an AC line gives you half wave DC. 4 diodes in an ac line in a full wave bridge formation, give you full wave dc..

 

[MinnesotaDaveChalmers]

My favorite video on the subject: https://www.youtube.com/watch?v=CW7I-ymfINU

I don't mind AC stick welding, 7014 works very well with it.

 

[Shield Arc]

7014 works very well with it.

I've read where guys who run really big 7024, rather run it on AC.

 

[skyhook]

Filtering, smoothing,a nd filling the holes , for the purposes of capacitors and filtering rectified ac to dc, they are one in the same. filling the hole is the 'smoothing' ...

No, they are not....cap's will smooth out a "peak" sine wave that has been "rectified" by "yes" diode's or a rectifier, they will not change AC to DC, ( fill in the hole, for the laymen term from a zero volt and up ).



No.. diodes are used to convert the ac to dc. in simple terms, a single diode in an AC line gives you half wave DC. 4 diodes in an ac line in a full wave bridge formation, give you full wave dc..

I think thats what I said, the cap's "smooth" this DC wave out.:confused2:

 

[Oldpath05]

When I started welding, it was on an old AC Sear's welder, somewhere around 175-200 amps or so, in ten years of outside welding, I've gotten bit on a few damp days here and there while putting rod in the tongs, but I never did or need to hold the ground clamp with one hand and hold the tongs with the other. There have been some damp days that I had enough of the jing-a-ling when putting the rod in that I started grabbing the rod with tongs. I think that's another benefit of mig welding.

I had a Century 250 amp AC-DC for 20 years(burnt up in shop 3 years ago) love to find another one. Nobody had mention this but the best thing about 200 amps of DC power is Carbon Arc Gouging, other wise known as, welding rod eraser, with a air compressor, a gouger,and 3/16 carbon, a lot of stuff that's welded together, with 1-3 weld passes can be easily be take apart with very little base metal damage.
For DC welding, here are some of the electrodes I liked and kept on hand. DC welding>7018, 11018, 6010, 6011, and on rare occasion, aluminum rod.
On AC, I liked 7014, I always tacked everything with 3/32 7014, then weld with 1/8-3/16, 7014 is a easy start, fast, strong rod in all positions.

 

[paulsharvey]

I bought AC/DC on everyone's advice, and I don't notice a night and day difference. Mine has lower DC max amps then AC; as do the Lincoln AC/DC tombstones. As for rods, I think the most generalist rod, as in, if I could only have one, I would have 6011 in 3/32". It will run from 70-130 amps, and weld fairly thin to fairly thick stuff if you work with it.

Edit: as a note, I don't think I've ever welded on virgin metal, it's all scrap, or rebar, or reused/repair, and is rarely as clean as it should be, so that affects my rod choice