Peter (peabo) Olson wrote: > The mind-bending moment occurs towards the end, when he tries to find the > circuit which charges the backup battery. It seemingly is not there.
Yes, but I didn't want to spoil the big reveal. :-) > Imagine the same H-bridge when line input is available. It is sort > of backward. Enough that the protective diodes of the MOSFETs are > conducting. It seems a bit overly convenient that the protection diodes happen to have adequate current rating to work as a charging power supply. But I guess the specs align with the requirements. (Or they're using custom MOSFETs in their H-bridge.) > Well it is a little more complicated... Yeah, I would have like to see him take the next step and figure out how they keep the forward and reverse currents isolated on the DC side, and how they regulate the charge current. This perhaps explains why the control electronics in most UPSs behave strangely (random blinking lights and unresponsive buttons) when the batteries fail. They lack an AC power supply, and must depend on the battery voltage to run the electronics, so if a failing battery is drawing a lot of current from the charge circuit, the electronics see an under voltage. (Not a completely satisfying explanation, because butteries often fail (have no capacity) without drawing high charge current.) -Tom _______________________________________________ Hardwarehacking mailing list [email protected] http://lists.blu.org/mailman/listinfo/hardwarehacking
