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AC vc DC arc welding question...

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  • AC vc DC arc welding question...

    I have a 225/125 AC/DC stick welder, and I have a quick question about using DC over AC. I've been using the machine mainly on DC+, but have noticed the max amperage on DC is 125a. Now, in AC, it will max out at 225a. My question is, will the capabilities of the machine (welding heavier gauge material) be greater on AC than DC considering the amperage max for each? In other words, what will be the difference in material thickness I can weld on 125a DC vs 225a AC? Thanks!

  • #2
    If you make enough passes, you can weld anything with that machine on DC or AC. Unless you get arc blow problems, you'll really never need the AC. Cary would tell you to break off the knob after setting it to DC+

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    • #3
      Penetration

      Mac is right there really is no use for the AC on that machine. If you are woried that you aren't getting enought penetration for what you are welding I would try using a 6010 or 6011 welding rod which would give more penetration at lower amperage then cap it with a 7018 rod to make it look pretty. Just words for thought
      Miller XMT 304
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      Torchmate CNC

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      • #4
        For the same number of passes, it will weld thicker material on AC. The main reason that DC (although giving a higher quality weld) is lower output is that the circuits to rectify the AC output of the transformer to DC have losses, and cannot deliver as much heat to the weld. When you switch off the DC, you bypass these rectifier circuits.
        Lincoln 175HD
        Miller Thunderbolt AC/DC
        Smith AW1, Dillon (Henrob) Mark III & Smith Quickbraze Little Torch

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        • #5
          smyrna5, the rectifier is connected to the low tap of the transformer which gives a lower amperage. I think this is done due to rating of the transformer when connected to a rectifier circuit.
          What do I know I am just an electronics technician.

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          • #6
            Originally posted by Mike W View Post
            smyrna5, the rectifier is connected to the low tap of the transformer which gives a lower amperage. I think this is done due to rating of the transformer when connected to a rectifier circuit.
            Even worse. I would think that it is done because the rectifier can't handle the full power of the transformer. At any rate, it will put out less power than the AC output, as we all agree.
            Lincoln 175HD
            Miller Thunderbolt AC/DC
            Smith AW1, Dillon (Henrob) Mark III & Smith Quickbraze Little Torch

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            • #7
              Since the size of the rod generally determines the amperage and 125 will run most 1/8 inch rods, unless you building bridges or battleships in your garage you're probably okay. I will note that my Stickmate goes up to 160 DC and I run 6011 at 125 most of the time with good penetration and nice transfer.
              Blacksmith
              Stickmate LX AC/DC
              Big cheap (Chinese) Anvil
              Hand cranked coal forge
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              HH 210 and bottle of C25

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              • #8
                Dad started out on his farm with a Lincoln AC225 over 30 years ago. About 10 years into it, he added a Miller AC-DC converter on top. After that, he used it on pure AC less than a handful of times.

                It's in my garage now, because we bought him a Hobart Stickmate for christmas here a couple of years back. The plugs had been in place so long I couldn't unplug the DC from the AC, or get the cables out of the DC box. I had to pull the covers and tap them out from the backside with a pin and shine them up.

                Just for kicks I tried AC with some 6011 and 7018. AC just throws sparks and spatter all over the place. The DC arc is very smooth in comparison.

                So, the whole "set it to DC+ and throw away the knob" is pretty accurate.

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                • #9
                  Well, I only use 1/8" rods (usually 6011, 6013, or 7018), and I rarely weld anything over 1/4".

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                  • #10
                    What's your duty cycle at 125A DC?

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                    • #11
                      According to the Lincoln website, its 20% at 125a DC (20% at 225a AC).

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                      • #12
                        Okay, that's standard for those types of machines. Enjoy!

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                        • #13
                          Thanks for the info!

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                          • #14
                            For big flat welds the AC 5/32 7018 works great. Very smooth and great re strike. I have use these machines a long time. I don't even stock an stick electrode bigger than 1/8. This is the type of machine I use for stick work around my shop. Never had the 300 hooked to a stick. Most any big stuff would be vertical and for the small amount we do its just as easy to run another pass. Here most stick work is 1/8 6010 and 3/32 7018, nice for control on light work. Most of the time we use wire.
                            I have ran these machines way beyond the duty cycle and then some. My shop is fairly cool which helps I am sure but it never even occurs to me to think about it.
                            http://www.facebook.com/cary.urka.urkafarms

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                            • #15
                              Hi all, the other day I had the good fortune to be able to do some welding using DC as opposed to the AC that I've been doing on and off for years.
                              I've got a 200 amp SIP coppermate welder and as it's a straight AC welder I always used it in this manner.
                              To cut a long story short, a coupla' years ago I aquired a welder attachment that connects to a regular AC welder and gives various outputs from Stick, mig and tig to name a few and both AC and DC with normal and reverse polarity as well.
                              I thought I'd try the thing out as it was diagnosed faulty years ago and got put under the bench.
                              It turned out the welding dealer wanted to sell me a tig welder and ran the attachment idea into the ground.
                              In the end the problem was found to be in the earth cable, and due to a bad connection at the plug in end and also at the clamp end resulted in a huge current drop just as the arc was struck.
                              Having fixed this problem and found out that it was actually working, I decided to find out what DC welding was like.
                              My best welds have always been classed as 'crow poop on barbed wire', and led to a lot of grinding out and rewelding.
                              I can only say that I will never go back to AC welding.
                              Using DC with 3.2mm rods and 120 amps, resulted in a continuous bead with no stopping or daggy lumps with slag holes and bubbly weld bits that I've been used to.
                              I noticed too that there was an almost complete lack of spatter.
                              The flux fell off the weld area as opposed to being hammered off, like before, with a welding chipping hammer.
                              The job I was doing was some steel boxes made from 100mm thick walled square tubing, 120mm long, and had 6mm thick plates welded on the ends to close them in.
                              I veed the weld area out on one end, on both edges of the plates and tubing, but on the other end just left the plates about 2mm away from the tube end, without a chamfer, to see how it welded, as the wall thickness was about 4mm.
                              The unveed weld went on just as well and saved a lot of veeing out.
                              The boxes are for the base of my milling machine and are bolted to the four corners to allow a pallet truck to get under when it has to be moved one day.
                              I almost came a cropper here, as the mill head had been moved to the horizontal, to get it through the workshop(garage) door, and when the blocks were bolted on and the head raised vertical I had 2" of clearance between the motor and the roof.
                              I can quite see the reason that the cheap hobby welders are all AC as it costs a bomb to add a set of diodes and an inductor to just do a bit of welding.
                              However, unless I've missed something in the excitement at doing a decent weld, it will be DC from now on.
                              I welded 5/8" BSW nuts to the middle of the end plates and had to grind the galvanising off.
                              Now I've got to learn how to get a good weld in a corner as the weld wasn't something to write home about.
                              I'm getting a blotchy weld with areas on the nut and plate not connected.
                              I might need to put the amps up a bit to allow for the extra thickness of the nut absorbing the heat.
                              I certainly wasn't getting a fillet, more like a blob on the nut and a blob on the plate with a bit of flux between.
                              I'm going to try using a 2.5mm rod to get in the corner and use the same amps, then run over the top again with a 3.2 mm rod when the corner is filled up.
                              I have the same problem with welding into a 90 deg corner and have yet to get it right.
                              Ian.

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