Check out their pdf manuals for details. I think all syncrowaves had a choice of voltages, but the choices varied. Some offered 240V. Mine had the option of 208V which works OK on a 240V supply. With mine I had to open the side cover to find out which voltages were covered.
I assume you are talking '70's and '80s machines like mine. Bear in mind they are huge machines - not something you can hide in a corner, and they will trip supplies with the inrush current. Mine is happy on a 40 amp type D breaker, but would trip a 40 amp type B. Ideally I've have it on a 110amp supply for the full 375 amp output, but I only weld thin stuff so haven't troubled the 40 amp breaker.
Naah - mine is a Synchrowave 300P (p for really efficient) dating from 1979. Not quite sure when they started but they did go on for about 20 years.
Funny you should mention the current - must be non-linear as I've done some accidental blasting with mine while getting used to the foot pedal without blowing the trip.
Voltages do vary - you'd have thought a welder sold in the UK would have jumpers for 415V (2 or 3 phase) and 240V, but mine was 415V and 208V. Alabama spec I think.
Hmm, did not think they went that far back. Looking at the schematic, I can see mid-70's parts used.
Most single-phase in the US is 220V (110V * 2). Three phase is 208 (110V * 3).
Then there is 220 3-phase, 240 3-phase, 380 3phase, 480 3-phase and 575 3-phase. You need to be a huge plant to get anything over 240.
Add to that, 110V is actually 120 (117 is nominal). 220 is actually 240. 380 is likely to be 415. So, they can handle a considerable range.
So they just picked something close for overseas. I bet with 50HZ, they had to add windings and dropped some taps to make room.
The "p" just adds a capacitor across the power. Basically a motor run capacitor. My Airco has 2 (and still wants 108A .)
Yes, the power draw is a square law. 28V out may be 100A, 40V may be at 200A. That is 2.8KW and 8.0KW (arbitrary numbers.) As the current increases, so does the voltage. Like running a 100W 240V light bulb on 110V, it will run at 1/4th the power.
The design is similar to the Aircos with the addition of real-time current cntrol (analog computing ) The control is vary non-linear. My Airco has a 20-220A range. Set the current to half and it is about 70A (if it was linear it would be 120A.).