New Dynasty 700 HF Starting Problem

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Just hooked up a brand new Dynasty 700 in an automated system at work and could not figure out why we could not get the high frequency arc starter to work.  We confirmed that the welder was producing HF, we could hear it in the machne, and see the assocated interferance in the remote camera on the system, but no arc.  Finally with the tungsten virtually touching the workpiece we could get an intermittent arc start.  We checked all the connections, bypassed the rotating ground (work connection), changed tungstens, turned out the lights and looked for stray HF throughout the welding station, nothing.  Finally we removed the calibrated shunt/ammeter that was inline to verify amperage and now this thing starts the arc better than anything I've ever seen.The shunt is rated at 500 amps and looks to made of 5 brass plates about 1/8" x 1" x 4" that are stacked on top of each other with air gaps between, and these are brazed into heavy connection blocks and either end.  This is connected to a meter that converts the voltage output to a amperage reading.  So I have no clue why this thing would kill the HF, but it sure did.
Reply:Would be nice to have a picture of the shunt.My guess is that the shunt was acting as a capacitor to the HF.  Suggest you use a DC clamp meter instead to measure current.  My fluke is capable of measuring up to 1000Amps AC or  DC without affecting the circuit under test."The reason we are here is that we are not all there"SA 200Idealarc TM 300 300MM 200MM 25130a SpoolgunPrecision Tig 375Invertec V350 ProSC-32 CS 12 Wire FeederOxweld/Purox O/AArcAirHypertherm Powermax 85LN25
Reply:HF/HV is a different animal. From my limited understanding, the shunt (by nature) is a giant inductor. HF loves inductors. I can't really explain the technical aspects, I do however know that if you take 6-8" of wire, coil it around a pencil, and point the 2 ends together about 1/4" away from each other and stick it in a microwave, you will get a sustained arc between the 2 ends of the same wire. The inductor may have been big enough to absorb all the hf.Miller: 200dx, Bobcat 225, Passport, Powermax 45, Milwaukee: Dry Saw, MagDrill, grinders
Reply:Hi pulser,Is there a reason you want to verify the panel meters on the Miller? I have to agree with the above post about the shunt acting as a capacitor. Also, inverters work by pounding rapid pulses down the pipe to the work so anything like that may change the actual output some.Maybe Steve can come along, but I'll bet the meters have to be set using a resistance load bank.Matt
Reply:The shunt is certified to NIST standards and is used to verify or calibrate the automated weld controller, panel meters, and the data acqusition system on the weld station.  It doesn't have to remain in line, we can just install it when we need to verify the current settings are accurate.  We've ordered a load bank to use in calibrating this system, since it would be difficult to run a 500+ amp arc for very long while you are trying to verify meters and adjust the controller output and feedback.  We prensently run an arc on a large chunk of copper while calibrating up to 300 amps, and things get real hot and sometimes ugly.Last edited by pulser; 10-01-2010 at 09:58 AM.
Reply:I am not sure if the 700 has the older style HF points, but if it does, you might could change your point gap a little to  compensate.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:It doesn't.  (have the old style points)Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:If you can wire the ammeter into the ground lead that should solve the problem.  Doing this will correct any inductance or capacitance from affecting the HF.  BTW: you will have to reverse the polarity of connections on meter compared to the way they were when in hot lead.Uncle TomLast edited by Uncle Tom; 10-09-2010 at 04:43 AM.