As said before the floating supplies do not have a ground reference. Think of a floating supply like a battery. They are independent of the ground reference and of each other. I can put one battery on top of another (In series) and the voltages add up, the same is true for a floating DC system. Isolated DC to DC converters provide floating DC outputs. You can also use a floating supply as a negative or a positive supply by simply tyeing the opposite polarity to the circuit reference. Grounded systems all have a common ground reference and can not be put in series, they must reference the system ground.
I think they can still be put in series. In a large truck, the frame is the common ground, while the 6 volt batteries in series produce 12 or 24 volts.
dc system
Re: dc system
