Down load the owner's manual form lincoln. Find the welding chart. Gives rod sizes and suggested weld amps. I think you won't have any problems welding. Just watch the duty cycle limits and don't overheat the welder.

 

I already have the printed manual that came with my AC225S. It also covers the AC/DC 225/125. 1/8" rod is right up near the top of the DC range. Thats why I ask the question.

Have you noticed anything loss in stability when you run run AC/DC 225/125 at the top of the DC range?

 

Does the 125ADC setting have reduced Open circuit voltage?.

Yes.

Because of using common parts, I wonder if the 125DC setting inherits reduced OCV from the 225AC setting, which was necessary to accommodate 230V 50A supply..

Partially right.
The transformer of the welder is designed to have a certain inductance that limits the no load input power. At full 225 amp AC output, the current is limited by the maximum voltage tap of the transformer. Note: With these machines, you don't really adjust amps directly, you switch voltage taps on the transformer secondary - the higher the voltage, the higher the current - to a limit of 225 amps AC.

For DC, the AC current passes through the voltage selector switch and then through the full-wave bridge diode bank (rectifier); this causes a drop in output voltage of about 2.8 volts (1.4 volts for each diode in use at a given time in the cycle). The current then passes through an inductor (to stabilize the DC arc) but this also drops a volt or two. Finally, on the Lincoln AC/DC 225/125 the DC current passes through a circuit breaker. The net result is that at each current setting, the welding voltage available is about 4 to 6 volts lower on DC that the voltage available on AC. This means reduced DC current output at every amperage setting. e.g. On the max amp setting, you get 225 amps AC but only 125 amps of DC.

I am considering replacing my Craftsman 35-230A with a Lincoln AC/DC 225/125. However, if DC settings for 1/8”rod have wimpy OCV, I’ll just get a plain old AC225S. I love the stable arc and simple setting of AC225S. Never used one with the DC option.

Personally, I like the Lincoln AC/DC 225/125 machine - nice arc on DC and 125 real amps will run most all 1/8 inch diameter rods. I've owned about 6 AC 225s and 3 AC/DC 225/125 units... sold them all off.

For me, the best old-time transformer welder with combo of AC/DC power and weight of only 15 - 25 lbs more than the Lincoln AC/DC 225/125 is the old Linde AC/DC 250 - 250 amps of either AC or DC! For sure the Lincoln Idealarc is better but... for me... not at 300 lbs!

I hope this helps - just my experience and my personal view on this.
Good Luck to you! :drinkup:

 

Thanks for taking the time to give me all the information Rick.

What I was trying to get at about accommodating the 230A 50V supply:
For 135AC settings and lower, I measure 77V open circuit. So those settings appear to have a common turns ratio and must be switching in different inductance. Above the 150AC setting, OCV drops off, so we must be selecting different turns ratios. At the 225A setting I measure 54V open circuit. That makes sense to use a lower turns ratio up there, otherwise at full load, it wouldn't stay within the available 11.5KVA.

Now if 125DC shares a tap with 225AC it would have the reduced turns ratio too, even though it wouldn't be required for the 11.5KVA limitation. But I don't know if it uses a common tap or not.


I like the Darth Welder photo.

 

Amateur, I wouldn't get to hung up on the open circuit voltage.
What counts more is the actual voltage while welding.
e.g. I have two welders that can put out 150 amps DC, one at 22 volts, the other at 30 volts.
The 22 volt arc is soft; the 30 volt arc is rather fierce but I like it - more forgiving.

 

Rick V has got it...Low or lower OCV is only a concern in STARTING AN AC arc. When on DC, lower OCV will start a DC arc without any problems...AC arc requires higher OCV .
Arc volts are listed right on the machine electrical plate. The 225 machines are rated 25 arc volts. The bigger 250's are 30 arc volts. The 300-400 amp jobs are 36-40 arc volts. It is the ARC VOLTAGE that effects the arc drive, stability, and performance of the welder..more so when welding with AC, some what less so on DC.

 

Thanks guys. My stick experience is only 3 different welders that do 42, 50, 65, and 79 VAC open circuit. I found the higher the voltage, the better the result. With the one that has 79VOC, I can usually restrike 7018AC without removing the tip, and I don't have quirky differences between rod brands. You can see why I might be hung-up on OC voltages.
.

 

I found an interesting link...

http://www.millerwelds.com/resources/articles/index.php?page=article108.html

I'm guessing the buzz-box type machines I am likely to use have the simple "drooper" I-V slope, and if OCV determines the I-V slope I think it might be important.

On the other hand, I think the more complicated curves might apply the the kind of equipment you guys might use, and I see OCV does not determine the slope of the I-V curve on those.

I tend to geek-out about stuff like this. Thanks for tolerating it.

 

I was just about to post something yesterday about the slope and the OCV. Read the part about OCV in the picture attachment for post #21 here. It came out of my old Lincoln arc welding handbook. Some of the old Lincoln stick welders had a voltage or dig adjustment. I even saw an old Lincoln buzzbox circa 1950 that had a switch for that.

http://www.shopfloortalk.com/forums/showthread.php?t=27659