High frequency in old transformer welders

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I just had a visit from the Miller representative. He demonstrated a Dynasty 280. I will buy one, but it takes me a while to wrap my brain around an expenditure that big. He seemed knowledgeable, as I have years of electrical training, with a pretty good understanding of how electricity works, I hoped he could explain the difference between the Dynasty and my Dialarc 250 HF TIG. Ultimately, I'm now unsure whether he didn't know, or as his job is to sell new welders, he didn't choose to answer the question. Instead he launched into a involved pitch on the virtue of the Dynasty variable wave shape.I install inverter frequency drives for motors, I couldn't rebuild one, but understand that they invert 1,2, or 3 phase AC to 1 phase DC, then in turn, convert that DC to chosen frequency and voltage AC. Hundreds of parameters can be programed. Programing one can take all day with an expert talking you through it. Some are web connected so the wizzard 6 states away can program remotely. The magic of electronics is often understood only by the engineer who designed the item. To troubleshoot all of the electronic components without a troubleshooting manual for the specific machine would be a daunting task. I'm guessing a modern TIG welder is similar in that it is a box of mysteries that 7 billion people don't understand.An old Dialarc is not so complicated. Someone understands how it makes high frequency. It had been my assumption that the HF option created secondary sinewaves in the power delivered. Miller rep says no, it only makes the 60 cycle sine wave look like it was drawn by a man suffering from Parkinson's Disease, it serves no function in welding! I'm betting Millers sales literature from the day said otherwise. A lot of people paid extra for this option believing it was usefull at the time. I don't have one to ruin, but scrapping a welder is a real learning experience. I once scrapped a monster Hobart industrial, and Westinghouse post war 600 amp engine welder, fascinating!Could someone explain how these spark gap devices increased frequency, and or improved a weld?
Reply:On older transformer welders like the Dialarc, the welding power for AC was a 60 Hz. sine wave.  Later ones like the Synchrowave had circuitry to more approximate a square wave to help sustain the arc.  In either case, the high frequency was an added circuit to help establish and maintain an arc when welding.  I think they are a spark-gap type oscillator circuit, somewhat akin to a Tesla coil setup, though lower voltage.Modern high-end inverters have all kinds of control on the output (welding) waveform and frequency, but still incorporate HF.Last edited by Oldendum; 01-11-2014 at 01:05 PM."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:I think both you and the Miller rep are correct. What the rep described is what you would see on an oscilloscope. That display is a 60 hz sine wave with a higher frequency signal superimposed on it.---Meltedmetal
Reply:The high frequency allows you to start an arc without touching the tungsten to the work. it creates a thin "arc" between the tungsten and the work that the large, high amp arc can follow and be established. This is very helpful when tig welding DC but is absolutely necessary when tig welding AC in which the high frequency is always running while welding, not just when starting.If you are new to tig welding (it sounds like you are) then a dynasty would probably be overkill for now. I would look at an old transformer machine "with high frequency" first which will cost you probably 1/4 of a dynasty. Square wave machines are very nice if you plan on a lot of aluminum and can be found for pretty cheap, especially the large 300+ amp machines.If you have the $$$ a Dynasty cant be beat.
Reply:Originally Posted by sixtyThe high frequency allows you to start an arc without touching the tungsten to the work. it creates a thin "arc" between the tungsten and the work that the large, high amp arc can follow and be established. This is very helpful when tig welding DC but is absolutely necessary when tig welding AC in which the high frequency is always running while welding, not just when starting.If you are new to tig welding (it sounds like you are) then a dynasty would probably be overkill for now. I would look at an old transformer machine "with high frequency" first which will cost you probably 1/4 of a dynasty. Square wave machines are very nice if you plan on a lot of aluminum and can be found for pretty cheap, especially the large 300+ amp machines.If you have the $$$ a Dynasty cant be beat.
Reply:I think part of your issue might be that you are confusing continuous high frequency on a transformer machine with adjustable hertz on the Dynasty. Not the same thing.This isn't the Miller article I was looking for, but it does explain some that might help you out. I know there's a longer more detailed write up on Millers site that explains it better, but I can't locate it right this minute.http://www.millerwelds.com/resources...TAW-frequency/.No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by DSWI think part of your issue might be that you are confusing continuous high frequency on a transformer machine with adjustable hertz on the Dynasty. Not the same thing.This isn't the Miller article I was looking for, but it does explain some that might help you out. I know there's a longer more detailed write up on Millers site that explains it better, but I can't locate it right this minute.http://www.millerwelds.com/resources...TAW-frequency/
Reply:Originally Posted by Willie BThank you, a nice article on the inverter technology, it is well explained. I am still lacking an explanation of spark gaps in transformer technology and how they work, and what "high frequency" means in the old systems. I had guessed that the magnetic field collapses twice during each cycle (120 times per second) as the sine wave crosses the zero line. If current peaks at the same rate, as it rises jumping the spark gaps a secondary current is created causing a secondary magnetic field, inducing another sine wave superinposed over the first but not in sync. If I were right this would tend to prevent the arc from extinguishing as current direction reverses. I'm not claiming to be right, I'm guessing.
Reply:The spark gap breaks over and induces a ringing type oscillation into the high frequency winding.Usually between hundreds of kilo hertz to about 3-4 megahertz,depending on the components involved.The high frequency is high voltage,usually at about 3,500 volts.A capacitor isolates the low voltage part of the welder from the arc boost.
Reply:Originally Posted by BlueweldersThe spark gap breaks over and induces a ringing type oscillation into the high frequency winding.Usually between hundreds of kilo hertz to about 3-4 megahertz,depending on the components involved.The high frequency is high voltage,usually at about 3,500 volts.A capacitor isolates the low voltage part of the welder from the arc boost.
Reply:Yes, the high freq will jump to you when you forget the ground, or if you are sweating and lean your arm on the table Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Normal welding salesman bs old welders last longer and weld better ,no need for pulse arc or trimix gas .Remember you can scratch start tig and use a garden hose to cool a tig.Old tigs Miller,Lincoln P&H ,GE,Westinghouse Airco Linde will work fine and last forever.
Reply:The dial-arc is a triangle wave in AC. That HF system uses a spark gap oscillator around 2MHZ.A spark gap tuned L C oscillatorA 60HZ weld needs the HF to restart the arc at every zero crossing or the arc will pulse.The Dynasty uses an impulse arc starter. Because the AC frequency is much higher than 60HZ the arc does not go out. But if the arc does, the starter refires automatically. Because the Dynasty uses high switching, it can make any style wave form the programs tell it to.Your dial-arc will still be welding after the Dynasty has died of old age.