3 Phase Power

[fRED mCnEILL]

I realize thids isn't strictly wood relataed but it is shop realated so hopefully someone can give me an answer.

I am looking at buying a welder(Miller CP 200 Power supply 208v/ 230v/ 460v/ 520v 3 phase only) that runs on 3 phase power.

I currently have 3 phase power(220v) through a rotary phase converter to run my 5HP table saw.

Will this welder run on 3 phase power produced this way.

Perhaps Mr. Chritiansen will chime in here as he seems to be an expert on 3 phase.

Thanks

Fred Mc.

[Jason Roehl]

What are the inputs on the welder? How many amps? Your rotary phase converter is likely too small if it is for a 5 HP table saw (unless it's WAY oversized). My little 225A Lincoln stick welder needs a 50A 240V circuit, that's 12kW, or in the neighborhood of 12-15HP. Your RPC would need to be able to handle the input amps of the welder, so its full-load amps (FLA) rating would probably need to be at least as much as the welder's input, and I would guess that you would want a 25-50% cushion as well.

[Kent E. Matthew]

I don't know how much help this will be, but I asked a friend of mine who works on welders for a living. He said you are getting 3 phase through the converter that you described is running your saw motor backwards. I asked if that would run the blade backwards and he said no. If you can get 10 to 20 amps off the circuit you should be able to run the welder. The CP-200 is not that big of a unit. If its hooked up to 230v you should be fine. If it is hook up to 460v it will not work. Hope this helps. I don't understand any of it.

[Bill Brady]

You may not be able touse a rotary phase converter to run a welder. The manufactured phase is not a good phase to run lighting or readouts on a machine so it will probalby nor run the electronics on a welder.

[David G Baker]

I have read this question in another site and the overall opinion was that it is not a good idea and may not work good enough to accomplish what you want or need. I do not know the reason though.
A welding forum may be the place to ask the question.

[Rick Christopherson]

Yes, you can run a welder from a rotary phase converter, but I do not know enough about the welder to know what its current draw will be, so I cannot tell you if this will run from a 5 hp rotary converter.

I came across an eBay listing (obviously not a reliable source for specifications) that indicated that the welder will draw 33 amps per phase. After doing some backward calculations of the welder’s rated output of 32 VDC at 300 amps, this number seems like it may be somewhat accurate (somewhere between 23 and 33 amps).

The other thing that I don’t know is how your 5 hp converter is actually rated. If it is a 5 hp idler motor, then this welder will definitely exceed the capacity of the converter. On the other hand, if your converter was rated to run a 5 hp tool (the idler motor would be larger than 5 hp) then you may be able to skirt by with a slight reduction in the welder’s output power.

Oh wait, I just ran through some other calculations and you are way over the ability to run this from a 5 hp converter regardless how the converter is rated. Unless I have made a mistake (very likely) this welder will draw the equivalent of 10 hp.

It is possible to augment your existing rotary converter by adding an additional idler motor and tuning capacitors, but this is more complex than I can answer here, and I have not created a schematic for the concept. In a sense, you would be paralleling two converters, but using the prime converter as the starter for the second.

[fRED mCnEILL]

Actually, the RFC has a 7HP idler motor.


Fred Mc.

[fRED mCnEILL]

I have just been told that this welder runs at 16.4 amps @ 230 v 3 phase.

Does this mean that my 7 HP idler 3 phase converter will work?

Thanks

Fred Mc.

[Tom Veatch]

...
Oh wait, I just ran through some other calculations and you are way over the ability to run this from a 5 hp converter regardless how the converter is rated. Unless I have made a mistake (very likely) this welder will draw the equivalent of 10 hp....



According to my very simple and unsophisticated calculations,

32 (volts) * 300 (amps) / 746 (watts/HP) = 12.87 HP

Of course that's only if the welder is being used at maximum rated output. I suspect most of the time it'll be running at considerably less than 300 amps unless he's making single pass welds on some pretty heavy material.

[Rick Christopherson]

I have just been told that this welder runs at 16.4 amps @ 230 v 3 phase.At 1-O'clock in the morning, you found someone to tell you this? You've got some pretty good friends! ;)

Yes, based on these specifications, you can run the welder from your RPC, but you may still need to keep the power less than 100%. When fully loaded, you are slightly above the capability of the RPC, but not so much that it is a major problem.

To gauge how hard you can drive your welder within the limits of your RPC, you could borrow a clamp-on ammeter and check the currents flowing into and out of the idler motor (not the same as the line currents, but right at the motor). It is too late at night to fully trust my calculations, but if the current in the two input lines was less than 19 amps, then you should be OK as this is not exceeding the current rating of the idler motor. If your idler motor has a nameplate current rating, then trust that more than my calculations.)

[Rick Christopherson]

According to my very simple and unsophisticated calculations,

32 (volts) * 300 (amps) / 746 (watts/HP) = 12.87 HPSee! That's why I have been doubting my calculations all night. This is a DC power calculation, and by default, whenever I calculate horsepower, I just instinctively include powerfactor and efficiency as though it was a standard motor calculation. ....

Oh Wait a minute.... now you got me second guessing myself. I do believe that with the way I worded this the first time that my statement and calculations were correct. It would be drawing the equivalent of a 10 hp motor. Yes, in terms of a non-inductive load, it would be 9600 watts and this is 12.87 HP, but the equivalent motor horsepower must be in Volt-Amperes, so the powerfactor and efficiency are applicable, as far as an RPC is concerned, so the 10 hp is correct (I think).

The proper calculation for motor horsepower is:
HP = I x V x pf x eff / 746; where,
pf = 0.8 for a fully loaded motor
eff = 0.8 for a typical motor, 0.9 for a better motor

For 3-phase motors, multiply by sq-rt 3 (= 1.73). This is a good number to remember because it will also convert the current from the input of an RPC to the current on the input of the 3-phase tool.

[Jason Roehl]

Rick, if the output of the welder is 9600W/12.87(ideal)HP, wouldn't you want the input to be GREATER than that to allow for the losses in the welder (wire feed, transformer, etc.)? So that would get us back up to around 15HP coming out of that RPC...

Jason

[Bernhard Lampert]

When you hookup the phase converter, make sure that the manufactured leg is not hooked to any of the control circuits. The manufactured leg may float up to about 270V without a load...may be enough to kill a couple of circuits or just shut it down.

Cheers,
Bernhard

[fRED mCnEILL]

I just re-checked my RFC and it the idler motor(Baldor) is 7 1/2 hp.

How would one increase the output? Is it simply a matter of replacing the 7 1/2 HP motor with a bigger one. i.e. 15HP? Surely it can't be that simple. Although I must say how amazed I am at the simplicity of the RFC.

Fred

[Rick Christopherson]

How would one increase the output? Is it simply a matter of replacing the 7 1/2 HP motor with a bigger one. i.e. 15HP? The cheapest (and easiest) method would be to leave your existing RPC intact, but add a second idler motor in parallel with the original, except the new idler motor should have a separate disconnect that you operate only after the main RPC is running, and only when you need the extra power.

The second idler motor would need its own set of running capacitors, but I believe these would be smaller than they normally would if it was the main RPC. Because the main RPC is already giving you 3-phase power, you won't need a start circuit, and as long as the secondary idler has the run caps, it should not be adding any undue load to the main idler motor. Given all of this, the available current from the generated legs of the two idler motors will be additive. The two motors do not need to be the same size.

Power the new idler from a separate circuit just as though it was a tool motor. As a matter of fact, everything about the new idler would be the same as though it was a tool motor, except it is not under mechanical load and has balancing caps. I haven't actually done this, but the theory seems sound. If anyone has any reason this may not work as expected, I am open to critique.

I get the impression that you purchased your existing RPC, so you may not have seen my article on how to balance an RPC. http://waterfront-woods.home.att.net/Articles/phaseconverter.htm

[fRED mCnEILL]

As a worse case scenario, suppose I hook up this welder to my exisitng 7.5 HP RPC what can I expect? Am I just looking at degrading the performance or will I do damage to the RPC and/or the welder.

Incidently, I tried to build my own Static phase converter with your help but was not successful. Almost at the same time the RPC that I have became available for a couple of hundred dollars so I bought it.

Fred.

[M Toupin]

Fred, the Miller CP-200 is a 200amp machine. It's a fairly old model, early to mid 80's or so. Here's a screen shot from the manual. As you can see, at 230v it will pull 18.6amps. Very seldom if ever would you run your welder wide open though unless you're really welding some BIG stuff!

73087

I've heard of folks running welders on a RPC, but never actually used one being run off a RPC (unless you want to consider a diesel 3ph generator). I'd think you would want a 15hp RPC or gang two as Rick has suggested.

Other than the RPC size, on face value I see no reason why you couldn't run it on a RPC. The only concern I'd have is the stability of your current and what effects it might have on the weld. Unstable power can effect the arc output and create problems with the weld. I would guess that as long as the legs were balanced halfway decent it should be fine.

Mike

[Rick Christopherson]

The only concern I'd have is the stability of your current and what effects it might have on the weld. Unstable power can effect the arc output and create problems with the weld. I would guess that as long as the legs were balanced halfway decent it should be fine.

MikeI am not an expert on welders, and wouldn't pretend to be one, but if I am not mistaken, they are taking the incoming power and rectifying it to DC power. If this assertion is correct, then the RPC should not pose any problems to the final output weld. If I knew more about welders, I could probably even tell you how to modify the 3-phase welder to run from single-phase power. It just isn't an area that I have researched yet. I'd have to see some schematics.

[M Toupin]

I am not an expert on welders, and wouldn't pretend to be one, but if I am not mistaken, they are taking the incoming power and rectifying it to DC power. If this assertion is correct, then the RPC should not pose any problems to the final output weld. If I knew more about welders, I could probably even tell you how to modify the 3-phase welder to run from single-phase power. It just isn't an area that I have researched yet. I'd have to see some schematics.

I'm no expert on electricity, and won't even pretend to know or understand the inner workings of a welder, but I can tell you from experience that the input power CAN have an effect on the arc. There's a lot of different types and models of welders out there, I'm also fairly confident that there's a wide variety of inner workings in those various welders. To make a claim as above is a bit premature when coupled with the admission that your "no expert on welders".

I have no intent to start a urination contest here, but from personal experience I'll stick by my initial assertion "input power CAN have an effect on the arc". Let's keep it in the proper context here though. I made the initial comment in my previous post merely as a warning to Fred that he "may" experience a problem. That's not to say he WILL have a problem or even the extent of the problem. Even if we assume that there "may" be some degradation of the arc it in all likelihood would be so minor that the average hobby welder would never even notice it. So, like I said in my previous post, "I would guess that as long as the legs were balanced halfway decent it should be fine."

Mike

[fRED mCnEILL]

How would one go about making sure the legs were Balanced"?

My previous experience with an RPC was getting the capacitors, making a bunch of pigtails and attempting to make it work. I did'nt have much luck but will admit I gave up quite quickly when I was able to buy one reasnable(actually, quite cheaply) My further experience then was to plug in the RPC to power and plug in the saw and voila!-it worked. I turned to 3 phase because I got a SUPER deal on a General cabinet saw but when I got it home discouvered it was 3 phase.

But I'm not afraid to try different things with some help in order to achieve the results I want.

I already have a "tig" setup consisting of a buzz box I bought 40 years ago and added a high frequency arc stabilizer to it. Considering there is no foot petal to control the amperage I get along quite well with it. The "mig" setup I'm looking at is obviously a commercial unit and is VERY cheap because, I'm sure, there is zero demand amoung hobbiests due to the fact that it is 3 phase.

Thanks for your interest and help.

Fred Mc.

[Matt Meiser]

Fred, I'd give Miller technical support a phone call and see what they say. Or you could ask on the message boards they host. From what I've read their support is good.