Miller CP 300TS Haas Kamp Conversion And Questions

Hey all, I've been lurking for a long time as I've been dabbling with homebrew CNC. Now that I've picked up a cheap welder at an auction, I've got some questions because I can't seem to find that anyone has done this exact model. My brain is wired for 12v DC, so multiple phases of AC just don't seem to compute with me very well.

I've made a diagram that reflects my understanding of how this conversion is done. Would anyone that has a better understanding of this care to take a look at it and chime in? I don't have a ton invested in this welder but I'd like to leave the smoke inside of it.

It looks like I won't be using a bus bar since it is on the input side of the machine, so should I do something different? Do I need to make any adjustments to the slope transformer settings? It seems like none of the machines I've seen converted have had them or made any mention of them.

Thanks to anyone that can help, and thanks to Dave for making big power affordable to broke hobbyists like me.

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Yes, that will work, but as you noted, the contactor mod (changing it from delta to Wye arrangement) isn't possible with the SCR (non contactor) control...

...but you don't have to... just apply your 240v power to the transformer taps identified for 208, and it should be about right.

Any news, Greg?

Hey Dave,

Thanks for the reply, I'm glad to see you're still around and helping people with this mod.

I tried it using the 208v taps as you suggested, output was less than ideal but there is certainly the possibility that this machine has other problems. One thing that was interesting is that when I switched the polarity of one of the non-simulated legs, power increased quite a bit. I'm not sure what to make of that but power still seems pretty low.

I'm going to try cleaning up the transformers and some of the connections in the next week or two and see if it gets any better.

-Garry

Okay, look out for a burned-out contact, or a broken wire on the back of the terminal strip. In my experience, the soldered-on transformer connections on back get rather brittle over time, and when they break, all sorts of frustrating things happen.

One of the biggest challenges of this, or any other mod, on ANY surplus machine, is that one may not have any way of knowing wether the unit was in operating condition PRIOR to acquisition. I've found broken wires, burned up contacts, and even a bad ground-lead jumper (yeah, the braided one that they used as a 'shunt' for the current meter) all corroded away inside, thus, reading really high output, but producing basically none.

If one is certain they did everything right, there's gotta be something wrong elsewhere. Fortunately, these gals are inherently fixable, and EASY to work on.