Weak welder output! Rectifier bridge?

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I bought a new welder but am wondering if my old welder should be repaired. I didn't have time to wait for it to be repaired so I bought a new welder. The welder that needs fixed is a Lincoln SP-175 Plus mig welder. It is a 220 machine that worked well for a couple of years. Now it is only "half welding" with minimal penetration.  Someone I talked to on the phone said a rectifier bridge. Any parts numbers or sources for what is the most likely culprit for a welder that just has lost its penetration power.
Reply:It certainly sounds as though the bridge rectifier may have had one of the four rectifier diodes go open circuit.As there is still some welding power available, anything wrong with the transformer or mains wiring would cause total welding power loss.  The rectifier would have to be a pretty good bet.Cheers,  Tony._________________________________Transmig 310 + Argoshield LightOxy acetyleneOxy propanePrehistoric stick welder_________________________________
Reply:What would I look for in the manual to order these diodes and are the 4 the same part number ? Thanks so much.
Reply:I am an electronic engineer, but unfortunately am not familiar with the Lincoln.So I have a pretty good idea what the problem is, but cannot be more specific about the actual parts.Your best bet might be to remove the rectifier heat sink and rectifier from the welder, and get someone to test each of the four diodes with a multimeter.  The faulty diode will have part numbers printed on it, and Google should locate a local source of an identical replacement.Cheers,  Tony._________________________________Transmig 310 + Argoshield LightOxy acetyleneOxy propanePrehistoric stick welder_________________________________
Reply:Great idea, thanks.
Reply:Pull the rectifier out, and if you need more help, I am right here.Cheers,  Tony._________________________________Transmig 310 + Argoshield LightOxy acetyleneOxy propanePrehistoric stick welder_________________________________
Reply:Forget replacing a diode.  Single power diodes are expensive.  A complete bridge rectifier will run you less.  You just need something that will handle at least half the arc voltage (but I'd get something considerably higher), and the maximum arc current.This one is 200A.  Is that enough for your machine (I don't know the machine)?http://www.ebay.com/itm/MDS200A-3-Ph...item1c1fd4437aIs the arc buzzing more than you would expect?  With one failed diode, you'll only get half the wave, and that will buzz badly.
Reply:If it were my welder (I have a MIG Pak 15 - very similar), I'd check:1) the big output capacitor (Disconnect and check for a short), weld with it disconnected and see if there is any change.  No change likely means you need a new capacitor.2) the rectifiers.  Note: In my machine there are 12 small diodes, three in parallel in each of the four arms of the bridge.  Each diode should be checked in isolation of the others.  If that's the problem - buy new ones.  Depending on what Lincoln's price was, it might be simpler, easier & cheaper to purchase a manufactered bridge block off ebay and bolt it to a new heat sink.Edit: *** Oops I see rlitman already suggested that! ***Rick V 1 Airco Heliwelder 3A/DDR3 CTC 70/90 amp Stick/Tig Inverters in Parallel1 Lincoln MIG PAK 151 Oxy-Acet
Reply:Looks like I clicked post just a few seconds before you.One problem with paralleling diodes is that if one fails, you're pretty likely to burn out the others that are in parallel with it right away.If any quarter of the bridge has failed, you'll end up with a "half wave rectifier".  The buzzing will be easy to hear, and the arc will be very hard to maintain, not just because of lack of power, but because it is pulsing half on, half off, 60 times a second.The rectifier I linked to was a three phase bridge, but if you look at the schematics, just ignore two of the diodes, and it'll work fine as a single phase bridge too.Again, I don't know the specs of your machine, but I saw 300A bridge rectifiers on eBay  (also 3 phase by chance), that were more like $70, and I'm guessing that will still be cheaper than replacing a single diode from Lincoln, but you never know.
Reply:Rlitman,You are quite right about the increased buzzing, and the difficulty of maintaining an arc with only half wave rectification.But trust me, use a proper suitably rated replacement diode that is every bit as good as what Lincoln put in there in the first place.Get the part number off the original, I can then tell you exactly what it is, and a proper identically rated replacement may not cost as much as you might think.Cheers,  Tony._________________________________Transmig 310 + Argoshield LightOxy acetyleneOxy propanePrehistoric stick welder_________________________________
Reply:If you find the part that is needed Shop around, from personal experience I have found huge price differences! Anything with Lincoln or Miller stickers on them are a whole lot more than the same ones made by the same parts guy without the labels!AEAD 200LE, Lincoln precision tig 185, Millermatic 251, Spectrum 625 extreme, Victor torch , Smithy 1220LTD. and  Do all C-4 band saw ,  Always adding.
Reply:Originally Posted by houseoffireIf you find the part that is needed Shop around, from personal experience I have found huge price differences! Anything with Lincoln or Miller stickers on them are a whole lot more than the same ones made by the same parts guy without the labels!
Reply:Originally Posted by rlitmanForget replacing a diode.  Single power diodes are expensive.  A complete bridge rectifier will run you less.  You just need something that will handle at least half the arc voltage (but I'd get something considerably higher), and the maximum arc current.This one is 200A.  Is that enough for your machine (I don't know the machine)?http://www.ebay.com/itm/MDS200A-3-Ph...item1c1fd4437aIs the arc buzzing more than you would expect?  With one failed diode, you'll only get half the wave, and that will buzz badly.
Reply:Originally Posted by MoparfeverThat won't work. That's a 3-phase bridge. He needs a single-phase bridge. Plenty of those too. Don't know why, but that welder uses parallel diodes in the bridge.
Reply:Originally Posted by rlitmanIt will work just fine.  Look at a schematic for a 3 phase bridge and a single phase bridge.A 3 phase bridge is just a single phase bridge with two extra diodes (and one extra terminal).He just need to leave one phase terminal open.In my experience bridge rectifiers are much cheaper as a whole, than the cost of four diodes of the same power rating.  I've often used them to replace a single power diode, just because it's cheaper.  I couldn't say why, it's just what I've seen.If a 3 phase rectifier is cheaper than a single phase, then that's what I would get.When that welder was made, larger diodes were probably too expensive, so cheaper and smaller ones were paralleled.  It's a bad idea from the start, and unless you get a matched set, you shouldn't ever try to replace a single diode (although as I said earlier, you can be certain that an entire bank of paralleled diodes has failed anyway, so you couldn't replace just one anyway).
Reply:There is also the fact that the 200a was figured with 6 dies to handle the current,as a simple bridge you are only using 4.