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  1. #1
    Join Date
    Aug 2009
    Posts
    140

    Default AC SMAW on an inverter power source question

    To quote Monty Python "And now for something completely different..."

    The AC frequency on an inverter power source can be varied considerably. For example a Dynasty 200 DX can be adjusted from 20 - 250 Hz. This allows considerable flexibility in tweaking the arc shape and performance when using the GTAW process.

    A simple transformer power supply will simply output the same frequency as the input line typically 60 Hz (or 50 Hz in some countries). I would guess that AC welding rods were developed for use with 60 Hz long before inverter machines were available. So the question is...

    Would there be any advantage to running a SMAW rod at a higher frequency? Or perhaps with high frequency stabilization? Or advanced square wave vs. a sine wave?

    TIA,

    Ken

  2. #2

    Default

    I have always hated AC stick welding. Most people do. The one single advantage of AC is better control of arc blow. Every other aspect is inferior to DC so why would you even want to? If you had a Dynasty 200DX you could do some lovely DC stick welding with it. Inverters have smoother arc control than rectifiers.

  3. #3
    Join Date
    Aug 2009
    Posts
    140

    Default

    Thanks Matrix,

    I almost had a Dynasty 200 DX. I just got back from a not very local LWS. I was at a closer branch of the same LWS company Wednesday and asked them what sort of deal they could make me on a Dynasty. They called another branch which had one in stock, a "new, floor display" model and offered a REALLY good price if I would pick it up at the other branch. For a floor display it had more scuffs and scrapes than my 3 year old Diversion, it appeared to have been hooked up and the parts, plugs etc. which were supposed to be in the box were nowhere to be found. Something told me to pass on the deal and I did. End of rant...

    As to AC stick, I am after a Dynasty strictly for TIG. But as the stinger lead plugs into the same port as a TIG torch I figured that the same AC would come out and was just curious what a stick rod would do at 250 Hz.

    Ken

  4. #4
    Join Date
    Jul 2011
    Location
    NE Ohio
    Posts
    25

    Default

    It would sure be interesting to play around with. Still just AC though.
    Campbell Hausfeld 110V MIG
    Jo Ann Fabrics Hot Glue Gun

  5. #5
    Join Date
    Apr 2010
    Posts
    261

    Default

    This is an interesting read ... AC does have some other advantages.

    https://kb.osu.edu/dspace/bitstream/...pdf?sequence=4

  6. #6

    Default

    I've seen that old Le Tourneau article from the 30's before. It's basically a lot of paragraphs to really only say two things:
    -Reduced arc blow.
    -Better deposition rate. (due mostly to reduced arc blow)

    A few things they conveniently forgot to mention are:
    -They switched to AC welding machines because they were cheaper than DC machines and as a result they discovered an additional deposition rate benefit in the process.
    -They build heavy equipment so there is little need to weld thin steel which can be problematic with AC.
    -There's a much greater possibility that you can electrocute yourself while stick welding with AC.
    -It's easier to stick weld with DC.

    I didn't notice it the first time I read that article years back but this time I picked up on a claim they made of better mechanical properties in the weld deposit. I will research that a little but I doubt that there is any merit to it as I have yet to see a critical weld procedure specifically call for the use of AC current only. If it really does produce better welds you would think you would see that requirement every day for all kinds of purposes.

  7. #7
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,618

    Default

    Guess you never heard of AC/DC subarc, very high deposition rates. AS for electrocuting yourself with an AC welder, its quite doultfull unless you have a weak heart and were welding in a pool of water. You would have an equal chance of dying from a DC welder with the same senario

  8. #8
    Join Date
    Sep 2012
    Location
    AZ
    Posts
    46

    Default

    Quote Originally Posted by Matrix View Post
    ... they discovered an additional deposition rate benefit in the process.
    As compared to, say, a 100 A DC arc doesn't a 100 A AC arc have higher current peaks of +/- 141 A? If so, one can imagine a possible benefit over DC.


    Quote Originally Posted by Matrix View Post
    -There's a much greater possibility that you can electrocute yourself while stick welding with AC.
    Do you have a reference for that statement?

  9. #9
    Join Date
    Aug 2009
    Posts
    140

    Default

    An interesting article from 1940. Thanks! Perhaps it will catch on some day. Just give it a little time

    Ken

  10. #10

    Default

    Quote Originally Posted by cruizer View Post
    Guess you never heard of AC/DC subarc, very high deposition rates. AS for electrocuting yourself with an AC welder, its quite doultfull unless you have a weak heart and were welding in a pool of water. You would have an equal chance of dying from a DC welder with the same senario
    I beg your pardon? I ran a 3 wire subarc for the better part of a year in a large vessel shop. One head was DCSP, one head was DCRP and one head was AC and all running 5/32 or 3/16, so yah, don't worry, I've heard of it. I can see that you are kind of the king pin around here but I'm no newbie to welding. Maybe a newbie to this board but that's it. As far as the dangers of AC welding welding goes, just ask the older Czech, Serbian and Polish welders that come over here from the old country about it. They will tell you stories. Either way, that's all beside the point with regard to this discussion and the OP's question.

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