Don't know whether it's better, a single relay with high voltage coil would be enough.
when I were a lad the UPS used to have a serial port to tell the pooter that it had lost its food supplydoes your UPS have the same?
My question is how to detect the utility power failure
I make a circuit to test which breaker is for. It when power is off at a AC plug, a buzzing sound is made. Power in, no buzzing sound. You can simply modify to use with the Arduino. My design use a opto-coupler. And the AC transformer, I got from the garbage, extract the AC transformer. Here a schematic.
The optocoupler's LED could even be run direct from the mains with appropriate Rs and Cs.
QuoteThe optocoupler's LED could even be run direct from the mains with appropriate Rs and Cs. PLEASE not DIRECTELY from the main ( You know Murphy's Law - I anythings can go bad ) . Just use a CHEAP AC transformer... it more safer. That what I have in my design.