Help trouble shooting a HF 125

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HiI was using my HF 125 today and then it stopped working.  I have done the bridge rectifier/capacitor modification.  The welder powers on.  When I push the switch I hear a click.  The wire does not feed.  It sounds like a motor is trying to run.  If I touch the wire to what I am trying to weld there is a tiny spark.Where do I start to trouble shoot this problem?
Reply:If your wire feed motor wont turn, I'd start there. Take the wire all the way out and see if the motor turns then. Then see how much voltage you have going to the motor. I have no idea how much. Maybe someone else can say. Since you performed the rectifier mod and the unit AC from the factory, you should know how to bypass that stuff to eliminate the possibility of the problem being the rectifier or capacitor.
Reply:Looks like the bridge rectifier has failed.  It was a 150 amp 1600v rectifier.  I took the rectifier, capacitor and resistor out of the system and the welder works.
Reply:Good to hear you found the problem. Can you get one with a little higher amp rating? You would think 150 amp would be enough but I'd probably go a little higher if you can get one.
Reply:Was the rectifier a 3 phase or a single phase ?
Reply:The rectifier was a 3 phase.  The info I found online said that a 3 phase would work.  I bought the same rectifier referenced in that article.  I am concerned about buying the same rectifier again.  One thing that I like about it was the built in heat sink.  I am just guessing that the problem lies in the rectifier because I was not getting any voltage coming out of the rectifier.  My knowledge of electronics is limited at best and closer to none.  I don't know if a bad capacitor would cause no voltage at the rectifier.In looking at rectifiers some are described as "SQL" and others are "MDQ"  The SQL rectifiers have a heat sink and are 3 phase.  The MDQ rectifiers do not have a heat sink and come in either single phase or 3 phase.  What is the difference between SQL and MDQ rectifiers.Last edited by mickri; 01-27-2020 at 01:01 PM.
Reply:A 3 phase rectifier uses 6 internal diodes to get 150 amps.If you use a 3 phase diode as a single phase rectifier, you are using 4 of the diodes , so 2/3 of 150 amps is 100amps.You would need to use about a 250 amp 3 phase diode .
Reply:Thanks Bluewelders for the explanation on 3 phase rectifiers.  Makes perfect sense to me.  When I was first looking into modifying my welder I wondered about that very issue.  Not knowing diddly squat about electronics I went with what people online said about a 3 phase working.  I will get a single phase rectifier as a replacement.
Reply:Using two of the three phases in that rectifier, the two active legs won't be 180 degrees out of phase with each other. My first impression is the output would be DC of varying voltage because the phases don't work opposite each other like a 2-phase rectifier. Is this a theoretical or practical consideration?HF MIG-180 with all the mods.Grizzly H8153 Stick/Tig Pulse 130/160.Wards PowrKraft AC-230. Stick & carbon arc.
Reply:It is theoretical.
Reply:phasing is dictated by the inputs phase angle, not the diodes.  A 3 phase rectifier just means it has 3 diodes in one body, not 2.   the diodes never know what the other diodes in a rectifier are doing phase-wise.  I have a degree in electrical engineering so it's not just my "random welders opinion".Everlast 350 EXT       -        Thermal Dynamics Cutmaster 52         -         Rogue Fabrication M600 xHD tube benderMilwaukee 4208 Mag Drill          -         Shopmaster Eldorado Combo mill/lathe machine with DRO.
Reply:

Originally Posted by Chad86tsi

phasing is dictated by the inputs phase angle, not the diodes.  A 3 phase rectifier just means it has 3 diodes in one body, not 2.   the diodes never know what the other diodes in a rectifier are doing phase-wise.  I have a degree in electrical engineering so it's not just my "random welders opinion".