Converting a Miller CP-200(3 phase) to single phase

Another followup while I wait for the capacitors...................


I started to assemble the cabinet and the screw holes(1/4x20 I think they were) were mostly stripped out.
Some 1/4 inch thick aluminum stock worked really well for making some nut plates and affixing each one
to the cabinet with two 1/8 inch AN426 rivets. The cabinet is starting to look pretty nice now so happy
about that. I need to make a right side cabinet door with louvers or at least a screened ventilation inlet
so that will be the next project. Before I do that, I will make a trip to the scrap yard and see if possibly
that side cover might be there just waiting for me to haul home......
 
General question about buying old industrial welders. A lot of the auction ones I see say 70-100 amps input. If I only have a 50 amp circuit, could they still be used, just not at max power, or will they not power on?
 
Barncat said:
General question about buying old industrial welders. A lot of the auction ones I see say 70-100 amps input. If I only have a 50 amp circuit, could they still be used, just not at max power, or will they not power on?
Click to expand...

Sure, it would work, however the breaker would trip if you got into some really heavy welding.
 
Could they mean 70-100 amps total, so would it be 25 per phase at 3 phases, or 35-50 amps per phase on single 230v? Or are you looking at welding output current, which is at low voltage and (therefore) high amperage? I scratch my head over stuff like that more often than I feel I should...
 
The recent one at auction said the input was 3 phase, 230v, 70 amps. Does that mean 70 amps each phase? I have no idea
 
Barncat said:
The recent one at auction said the input was 3 phase, 230v, 70 amps. Does that mean 70 amps each phase? I have no idea
Click to expand...

It would be the total amps on the primary I would think. Otherwise you would have to use at least 1/2 inch rebar for welding rod!:eek 2:
 
Not sure on specifics but remember that most arc welding is @ 40-60 amps....

so using ohms law...you’re putting in 70 amps at 240v and converting it to “X” amps at say 60 volts.
Of course there’s some heat loss too.
200 amps less the heat loss would be my rough guess
60 x 240 = 12000
12000. / 60 = 200
 
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Another update for anyone interested...

I'm beginning to think that the 3 phase transformer has a short in it somewhere so the plot thickens. I think I will have
to remove all the secondary connections and power each part of the transformer separately to try to isolate the problem.
Likely I will power each section with 120 volts to try and find out where the difficulty might be. This may not be an
easy thing to do because all three transformers are on the same core to confuse the issue. If I can prove that the
transformer is defective, I will save the good parts and scrap the remainder.

If it ends up parted out, at least I will have a bunch of good parts and learned a lot about the intricacies of three phase power.
 
Egads! I think I have found the problem! I applied 120 volts from the center tap primary circuit of the transformer to each outer winding of the
coil that was seemingly drawing a lot of current. You can tell by the louder hum on that coil.
One side was fine and the other side dumped a 20 ampere breaker instantly. I suppose I could disassemble the transformer
and have a go at rewinding the primary or repairing the primary but I will have to give this a bit of cogitating to decide what to do for the next
course of action. I will have to scrap it if I don't fix it so might as well disassemble the transformer and see if I can find the problem
before junking it. Some transformer cores separate easily and not so for others so will have to see what happens. The transformer looks like
it weighs 100 pounds or so so expect it will be fun to just get out of the box, not to mention disconnecting all the heavy wiring. So anyhow
that where this project sits for the moment. If anyone has any great ideas, I would love to hear them.
 
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Well, the CP200 Miller welder has worn out it's welcome in the shop so am going to part it out I think. There are
a lot of good parts to save and the base I think I can use to make a stand for my new Everast 210EX TIG machine.
It's kind of a shame but it's time has come. I will save the meters, heavy 200 amp wires, the reactor(inductor),
and all the fittings and otherwise good stuff. I may be able to use the transformer for a stout battery charger possibly.
I can't part out the transformer for the copper and sell it to my scrapper friend because he gave me the machine free.
If I do scrap it for copper I will have to present my friend with a bunch of copper transformer wire to recycle, maybe a
new year's present for him.:)
 
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