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I want to convert a Lincoln AC welder to DC.

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gary350

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When I strike an arc it is a dead short on the transformer for a few seconds until the arc gets started.

I do most of my welding at 90 amps but that may have nothing to do with a DC circuit.

I am trying to decide how to build this circuit but I really don't have any good ideas.

I want to remove the welding cables and run some short 3 ft long cables to a AC to DC converter then attach the welding cables to the DC converter.

I have a welder like the one shown at this link, **broken link removed**
 
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There might be something wrong with your welder. I have that same unit, and I don't see what you're seeing. Or you might be trying to use rods that are too big. At 90A, 3/16" or 1/8" is about as big as you want to go. You might also want to monitor your 220V while you're welding. It might be drawing a little too low.
 
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There might be something wrong with your welder. I have that same unit, and I don't see what you're seeing. Or you might be trying to use rods that are too big. At 90A, 3/16" or 1/8" is about as big as you want to go. You might also want to monitor your 220V while you're welding. It might be drawing a little too low.

I have an AC welder and it works fine I use it all the time. I want DC. How do I make DC?

I know how to use diodes to make DC but from AC but how do you do it to a welder when you strike an arc it is a direct short it will fry the diodes. Diodes would have to be rated 1000 amp 75 volts unless there is some cool circuit that will work that I don't know about. I have about 50 electrolitic capacitors 200 volts 45,000. uf. a couple of these will make a good filter circuit. The welder is the current limiting transformer so mayby I am wrong a direct short might be limited by the setting. If I set it at 90 amps and strike an arc maybe it is limited to 90 amps. If so then maybe this will be easier than I thought I need some 200 amp diodes that gives me a good safety factor.
 
Gary, what you want to do is done with 4 very large "door Knob" style diodes and two steel plates. You basically are building a full wave bridge rectifier. You will have 2 pos biased diodes on one plate and two negative biased on the other and draw you leads from the plates and use a thick copper bar for the input bridges to the diodes. You will need lots and lots of cooling and a well insulated enclosure to prevent shocks, but it is easily done. PM me off line and I will explain further if you need more assistance.Good luck, hope this helps.
Bob
 
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Hi Gary

Given a choice I would use 4 diodes using the ones that carmusic inked to. They are designed for what you want to do. With a 200 / 225 amp welder they leave a nice overhead rated for 300 amps. Also, note from the data sheet they can be ordered with an anode or cathode stud so you want two of each. The 4 diodes will set you back about $100 at about $25 each. Also note that diodes like these stud mount type have 3/4" studs on them for the current. Next as was mentioned you will want several pieces of copper bar stock which is readily available from McMaster Carr Supply.

Years ago I would have suggested Bakelite as insulating material to build on but no longer seem to see it available? That leaves you possibly Garolite in maybe 1/2" sheets you could cut down. Also available from MvMaster Carr Supply.

No matter how you slice it and dice it this will be an expensive affair. You will also need some good high current lugs in copper or aluminum and I would go with copper like the set screw copper for 1/0 for welding cable. Finally some 1/0 welding cable something like this in 1/0 size.

I would make the unit detached so you can use it or not use it. Heat sink the diodes and make sure you have cooling fans. Again, an expensive proposition. Even going the home brew route.

You may want to check with companies like Miller or Lincoln to see if they market a plug and play rectifier assembly.

Ron
 
Gary, another member on this forum who may have the diodes and a circuit drawing is Hitech. He and I were discussing the exact same thing a while back so you might give him a holler and see what he has to help ya get going on it too. But like the others said it aint hard but it aint gonna be cheap either. You will loose a little top end amps but it wont be huge and you will have DC out and still be able to run AC as well if you do a neat job of wiring and use dinse type connectors.
Bob
 
Sorry 3V0, I was a little concerned that since there are high volts and very high amps involved it might be better to actually draw the device and discuss it in offline forum. I have no issue with it being online, if there is an interest I will be glad to attempt to do a drawing if that would help. Other forums I am a member of immediately lock these types of threads due to the volts and amps, so I was trying to protect the thread from being closed so the discussion could continue. The commercial equivelent is the HF251-D from miller, but it also includes high freq for tig starts. Lincoln and Thermal also offer similar boxes, but they are also quite expensive if I remember correctly
Bob
 
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Another source for the diodes is Ebay; **broken link removed** This guy has both polarities and many different sizes.

Or a dedicated welding rectifier, also on Ebay; **broken link removed**
 
Sorry to burst your bubble but I work on welders and plasma cutters rather often and know how they are built so I can tell you that converting an AC stick welder to DC is not as simple as using a set of big diodes.

The real AC/DC CC welders have an extra winding set on the secondary to boost the voltage and power to compensate for the drops associated with the additional DC circuitry. Also DC welders have a large inductor called a reactor coil that smooths out and stabilizes the arc. Without those all you will get is weld quality that is worse than what you have now with AC and just turning it up will not give any where close to the same effects.

If you are going to try it you will likely find that the parts involved are going to cost about as much as if you just went out and bought a good AC/DC welder.

The diodes you will need will need around a 1.5X amp rating over what maximum current you will run at and a 600 to 1000 Volt working capacity as well.
As far as the reactor coil goes if yo are lucky/clever you can get by with using a large battery charger transformer secondary as the reactor.

For the wiring and cable obviously you don't need anything heavier that what the welder came with so for a old Lincoln AC 225 buzz box welder 4 gage was normal and 2 gauge is plenty big so you don't need 1/0 or stuff like that.

When you are all said and done don't expect all that great of welds anyway being you're trying to turn a econo welder into something it is not and was never intended to be.
 
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And there you have it from a guy who has no shortage of welding experience. I liked the trailer from scrap which can be found here. So you can't make a silk purse from a sows ear. :)

Thanks tcmtech
Ron
 
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