Hi,
I torn town another Eaton UPS today. I'm surprised it uses a transformer with only 3 wires altogether. Refer to the photos, they are Red, Brown & Blue. I measured the resistance between all of them. It's about 12 Ohm Brown-Red and Brown-Blue, about 3 Ohm Red-Blue. I guess it's an ”autotransformer" with only one winding. I hooked Brown/Red with mains 240V AC and tested voltage between Red/Blue I got about 32V AC. The voltage between Brown/Blue is about 270V.
From this, I think Brown/Blue is the full winding, and Red is in the middle. If I hook Brown/Blue to 24V AC [this should be 240V AC], I would be able to get 28V AC between Reb/Blue and 212V between Brown/Red. Is my understanding correct? I can easily have another test.
My main question, though, is - what's the point of not using a transformer with two separate windings which provides electrical isolation between the primary and secondary? Also, is this transformer good to be used in a power supply? (Its high capacity looks useful)
Thanks.