RPC & welding machines

[millman52]

Any rule of thumb for sizing of RPC for use with a welder.

[in2steam]

If you need a phase converter for a welder, you either need to find a new welder(gas powered or single phase) or reconsider your location, I don't think they have made a 3 phase welder for many many years. I doubt it would be cheaper to buy a RPC and install wiring vs buying a new or newer weld that can run on single phase. Its been my experience that they would be in the 20 30 HP range anyway(like a dynamotor or airco motor-genset style), thats a chunk of change. Just my 2 cents
chris

[millman52]

Originally Posted by in2steam If you need a phase converter for a welder, you either need to find a new welder(gas powered or single phase) or reconsider your location, I don't think they have made a 3 phase welder for many many years. I doubt it would be cheaper to buy a RPC and install wiring vs buying a new or newer weld that can run on single phase. Its been my experience that they would be in the 20 30 HP range anyway(like a dynamotor or airco motor-genset style), thats a chunk of change. Just my 2 cents chris

No I am talking about a 3 phase transformer type welder. A 400A 3 phase 220V that draws 65A. @220V. I have yet to find a single phase welder that will produce 350-400A @ 100% duty cycle. I don't think they even make one. Even the inverter type welders are 40-60% duty cycle on single phase. I could be mistaken but I don't think they will even produce the nameplate amperage on 220V single phase.....

You are correct about the motor/genset style I have a Hobart 300A that has a 15 HP motor on it. It runs fine on a 10HP RPC

[in2steam]

Originally Posted by millman52 No I am talking about a 3 phase transformer type welder. A 400A 3 phase 220V that draws 65A. @220V. I have yet to find a single phase welder that will produce 350-400A @ 100% duty cycle. I don't think they even make one. Even the inverter type welders are 40-60% duty cycle on single phase. I could be mistaken but I don't think they will even produce the nameplate amperage on 220V single phase..... You are correct about the motor/genset style I have a Hobart 300A that has a 15 HP motor on it. It runs fine on a 10HP RPC

I don't follow you on the being able to produce the nameplate amperage, please restate.

From what I understand, and I am no expert on transformers, with setup in a false leg RPC you will not be able to gain you full amperage anyway. You would be talking a on big mother though, esp if you would like to run 100% duty cycle. You will be drawing around a 115 amps on your single phase at your 65 amp load roughly, if you can hook it up that way.

I figured it was a 3 phase transformer, we do alot of printing for miller, I was into to work on saturday and pulled all of the face plates we had in stock the only one that they currently make that we had is deltaweld, and one other invision something other. They had 100%DC for MIG, at 450 amps @ 38V
I figured that was around 70 amps draw.
I found this web site and they had a chart for

http://www.americanrotary.com/rotary...onverters.html

I would have to say at least 20HP but more like 25 HP. The duty cycle might be your problem in the end, you may really have to bump your HP to get that. I went to school for welding the biggest machines I used were 400a Lincolns they had 50%DC I would hate to think what that was like, 2-3 minutes of that and I was crawling out of my gloves and capo at 100% uck a whole hour.

chris

[millman52]

What i was meaning about nameplate amperage Example: This is from Miller website on a XMT350 Nameplate being 350A :

Input Power

Requires 3- or 1-phase power
Rated Output

350A at 34VDC, 60% Duty Cycle, 3- Phase
300A at 32VDC, 60% Duty Cycle, 1- Phase

[in2steam]

Well yeah its making nameplate, thats what the nameplate says, you are derating for single phase, its what we used to call a conditional nameplate when I was working in motor testing. I suspect that you can get more out of it, but your weld may not be the best. What kind of electrical service do you have right now? I would be concerned about browning out if you really want to crank that baby up to its 100% power setting on CC. If you are welding on something that thick you are going to be needing 3 phase power to move it around too not to mention you will be buring through sticks like they are candy so 100% duty will be hard to achieve. I have used smaller cc machines on railroad applications, and boiler applications(on stayed surfaces), neither hit more then 3/4 power with 7018 and 5/16 rods, again I was getting hotter then the machine was, if I was hitting 60% DC I would be impressed it took me longer to get the rods out of the heater and into the holder then me to burn through the rod. Then again I would not consider myself a professional welder either, nor a novice.

chris

[Al_The_Man]

Originally Posted by in2steam not to mention you will be buring through sticks like they are candy

I assumed it was Wire feed (MIG?) not stick, hence the 35v secondary?
Al.

[in2steam]

The highest amp draw is typically through stick, you can do it on wire I suppose but it might as well be a stick at that point, 400A through a wire would be a neat arc, not to mention hot. I know I ran some bigger millers with shielded metal and gas, with wire that was close to 1/8, those were cool, well not quite.

Most new machines will run both, if not all three ways, tig, mig, stick. Miller has had big clunker switch on the front of there bigger units for a years to switch between cc and cv, now its a little switch.
At first I thought he was talking about a motor-gen set, never really thought about a regular 3 phase transformer, he must have a decent service to be thinking about that. I cannot even run a little buzz box without making my lights go dim at home.
chris

[millman52]

Yes I have a 400A Service entrance in one section of my shop And another 200A service in another section of the building.

I regularly weld at 300A MIG with a Hobart Genset type machine It is powered by a 15HP 3 phase motor. Running a 10HP RPC.

Which 300A is enough for any welding I do. There are occasions that 400A & air arc gouge would be really handy.

I am running a 250A 3 Phase 100% duty cycle Linde transformer type MIG welder, Also being powered by a balanced 10HP RPC. The welder will produce the full 250A (At least the amperage gauge on the front panel of the machine shows 250A when the welder is cranked up). Everything seems to work fine with it. The arc seems to very near as smooth as the Hobart generator machine. But then a true generator style welder arc is really hard to beat anyway.

My reasoning for wanting MIG welding equipment with 100% duty cycle is you simply cant over do the machines capability.

A while back I had a 250A Thermal Arc fabricator 251 Which according to the book is 300A 40%, 250A 60%. With running .045 wire & 250A We kicked the thermal out several times & had to wait on the machine to cool.

From briefly browsing Millers machines looks like about 300A @ 60% is about the best you can do on a single phase machine.

As far as electric consumption from the utility company. Just about anything is less expensive than $3.00 gal for diesel & running an engine drive machine.

The above facts topped with literally hundreds of good used 3 phase welding machines avalible for pennys on the dollar as opposed to new. Makes Consuming a few more kilowats pretty attractive.

[in2steam]

As long you as you have the service I would say do it, if you can pick up a cheap welder, and through in the RPC. If you are doing that kind of welding I can see how a arc gouge would be handy at that amperage...

I agree I have to fill up a gmc 6500 with a cat diesel on a regualr basis, it takes my full paycheck($3.10 a gallon) for that job(partime) and then some, I used to wonder why the boss yelled at me for leaving it idle too long.

chris