The last time this was asked I was curious so I set up a good stock generator on the test machine with a thermocouple tucked into the field winding, the test machine can go 6--12v with the flip of a switch
At 6V it merrily churned out 6 amps, the field windings at 110 degrees after 20 minutes, then flipped machine to 12V , the output went to 28 amps, and in 39 seconds the temperature climbed to 165 degrees and I aborted the test
56 volts open circuit
I don't know if the field temperature would have stopped climbing at a "livable " temp or if the 3rd brush could have been adjusted enough to make the outcome sustainable
With different field coils It should work
I have a 12V battery in my car , no modifications to the car, I cut the xtra volts out of the battery with a sawzall-- this way when I am asked if I have 12V because of fast cranking and bright lights I can say yes---but