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  1. #11
    Join Date
    Dec 2013
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    Quote Originally Posted by duaneb55 View Post
    No AC weld output on the new TB. Older versions had it and it's a shame Miller did away with it on the latest model almost eliminating aluminum TIG and preventing using AC stick to combat severe cases of arc blow. The thing is, the machine produces AC which is then rectified to DC so it's already there as it was when the TB had it. Not sure why Miller left it out of the latest version.

    Weld output is also 3 phase as apposed to the Bobcat's single phase which makes for a smoother although not exactly like a pure DC (i.e. SA200) output arc.
    How would the pure DC (SA-200) machines give flat line DC? I'm assuming a three phase AC then rectified supply would be similar to a three phase factory machine rectified for DC. Current never falls to zero, as two more phases not in sync. would also be contributing.

  2. #12
    Join Date
    Oct 2004
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    Edmonton, Alberta
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    The SA200, and other Classics don't have rectifiers, they are pure Generator output, as for the new Miller machines like the 325/350/400, they have a rectifier, however that output also has a high speed switch (IGBT), or IGBT'sl integrated to implement a designer wave form.

    Few really used the AC output of the 302, as it was unstable at best. Want to weld Aluminum. use a spoolgun

  3. #13
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    From memory, the Westinghouse had a lot of segments on the commutator. How many field poles I'm not sure. How many brushes I don't remember. I would think as a brush is reached by an armature coil. a surge of Dc would rise from zero, then fall to zero, and repeat. Wouldn't that give a rapidly pulsating DC?

  4. #14
    Join Date
    Jan 2012
    Location
    Appleton, Wisconsin U.S.A.
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    The Miller engine-driven welder/generator lineup has many multiprocess welding options that can help you be prepared for most anything, all with AC generator power. While the Trailblazer no longer has AC welding output, it still has AC generator power. When choosing a machine for jobs that require AC welding, Miller recommends either a Dynasty inverter plugged into your welder/generator, or consider a Bobcat or Big Blue Air Pak Deluxe.

  5. #15
    Join Date
    Aug 2008
    Location
    Orange, TX
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    1,215

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    Quote Originally Posted by Willie B View Post
    How would the pure DC (SA-200) machines give flat line DC? I'm assuming a three phase AC then rectified supply would be similar to a three phase factory machine rectified for DC. Current never falls to zero, as two more phases not in sync. would also be contributing.
    In a pure DC output generator, there is actually AC current taking place within the windings of the armature. Remember all those commutator segments on the Westinghouse? The pure DC output then is a result of the positioning of the field coils, the (+)/(-) brushes, individual windings in the armature and the relationship between the three.

    The AC current is induced in the multiple, individual armature windings as they approach, pass thru and move away from the (+) and opposite (-) poles of the magnet fields created by the fixed field coils. Because the fixed output brushes are wide enough to span two or more armature segments at a time, the slight rising and falling of the (+) or (-) voltage within each individual winding thus becomes a smooth uninterrupted output at the brush leads. This process has been referred to as "natural rectification" and requires neither an output rectifier or field voltage filtering capacitors to produce a straight line pure DC output.
    Last edited by duaneb55; 05-14-2014 at 12:36 PM.
    MM200 w/spot controller and Spoolmatic 1
    Syncrowave 180 SD
    Bobcat 225G Plus LPG/NG w/14-pin*
    *Homemade Suitcase Wire Feeder
    *HF-251D-1
    *WC-1S & Spoolmatic 1
    PakMaster 100XL
    Marquette "Star Jet" 21-110

  6. #16
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    Dec 2013
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    At the epicenter of the Green Mountain Range in VT
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    Thank you! Ive always wondered if the legendary weld behavior of these beasts, and their more famous Lincolns was because of brief interruption of current or no interruption. Now I know.

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