Question on my old Miller CP200 Haas Kamp conversion

Hello all
I know it's been a very long time since the Haas Kamp Miller CP200 single phase conversion was introduced on this forum.
I did perform a successful Haas Kamp conversion on my very old Miller CP200 and it has been (and still is) performing flawlessly for all these years.
The question I have is related to the factory designed max open circuit voltage which I believe was 39VDC compared to the after conversion open circuit of over 50VDC which actually pegs the voltmeter needle. This occurs with the voltage scale set at 36VDC on the machine's visual mechanical scale.
I have the welders slope set on high and the at this setting I get an open circuit voltage of over 50VDC and drops down to a welding voltage of 25VDC.
Can any one provide some insight as to what's going on or happening here? In as much as how the conversion results in these new operating characteristics?

jzr75601 said:

Can any one provide some insight as to what's going on or happening here? In as much as how the conversion results in these new operating characteristics?

Click to expand...

When the CP200's input was Wye, the transformer's 480v coils were running on 277v each.

Breaking the Wye centerpoint, and driving TWO of the three coils directly on 240v delta resulted in slightly less (240 instead of 277 volts, right? that is a reduction to 0.866... or about 13% LOWER)

This meant that the SECONDARY side would have been (in theory) 13% lower than original.

The secondary WAS a DELTA configuration... and the solution to bring that voltage back up, was to convert the secondary's DELTA to WYE, by removing connections at the output contactor, and applying a cross connection of the three output legs. This brings the LOADED output voltage back up by 13%...

But with the coils in series, they're actually showing a higher open circuit rise... it's a PEAK indication, rather than RMS... So that's ONE reason.

The second thing to realize, is that the transformer was originally running on three sine wave inputs 120 degrees apart. NOW, the two outer coils are being driven simultaniously, but 180 degrees out of phase... and the CENTER coil is alternating at SOME phase angle between 10 and 80 degrees out of phase from the A and C coils.

I say SOME angle, because the transformer core's flux between the two outer coils may be a fairly predictable thing, but the LOAD on the opposite side determines the amount of magnetic flux, and electric current, which will flow through that center core...

And...

The CORE is no longer going through a circulation once every 360 degrees of three phases... It is now going through MORE, because it's operating in 'quadrature'.

A transformer's output characteristics change with frequency, not just because of the COIL windings, but also because of the CORE.

What you're seeing, is simply a result of those circumstances.

Have you put a digital meter on it? If so, have you measured both OC and while carrying an arc? I would be willing to bet that the OCV indicated IS higher, but probably not the same as what your meter indicates. I'd also be willing to bet that the arc voltage is a little different, but proportionally similar to what your crank-tape indicator suggests.

The real question is: How is the weld quality, and how is it's consistency over long-term load? Are you getting good penetration, and is it staying good even when you work it really hard, for a long time?

New to this form business, I have picked up a cp200 that’s been converted to single phase. Started using it and got about 15’ of weld down( not continuously) and is just quit welding, still fed wire but no arc. I have same welder at work that is a 3 phase so I started digging into the problem and found that the contactor burnt up. The guy I bought it from had put a new contactor in so it wasn’t very old. The contactor had two of the three legs burned on it which doesn’t make sense to me and of course the correct contactor that’s supposed to be in my machine ( it’s a 1971 model) is obsolete and I don’t know if the reason it burned up is because it’s the wrong one or if there is other issues hiding in the machine. Any info would be great
Thanks

Try Larry at Weldmart in Texas, his numbr is (281) 432-0250. He has been very kind and helpful to me with my CP-200. He really likes this machine and I think he will help you.

Sorry for the late response, Hel- The contactors on these are old enough that they get kinda needy at times. Even in normal 3-phase operation, they needed to be cleaned on a somewhat regular basis, as they get jammed full of fab-shop dust and crud, and then the contacts don't land clean, and they arc a bit when they open. If you look at the newer versions, they phased out the contactor and went to solid state control via Silicon Controlled Rectifiers, which had a substantial advantage in maintenance.

I'm certain yours burned up just because it was overdue for some attention. Don't feel singled out, I've smoked two of 'em too...