Build a UPS

I am wanting to build an Uninterrupted power supply. I was planning to use relays to connect and disconnect and the mains and battery power. N/O for the mains and N/C for the DC voltage. I wasn't sure if the relays would switch fast enough for the CPU to remain on. I loaded 2 pictures. Has anybody ever built something like this? 

Picture of Build a UPS
ooda555 years ago
Running the inverter constantly is usualy your best bet (as lemonie suggested). However in my UPS i use a relay to switch between mains and inverter and my PC, CCTV setup, Ext.HDD and broadband router all stay on. This eliminates the need to find a high amp battery charger
My system is completley explained in this video if you are interested:

Good luck with your project!
lemonie5 years ago
Take the relays out altogether; run the inverter off the 12V batteries/charging supply - no switching needed.
It's less energy-efficient but will be "safer" & more reliable.
-How bad is your power supply?

WWC (author)  lemonie5 years ago
By taking the relays out then both the mains and inverter will be supplying the CPU at all times? So when the mains go off the inverter will still be working because of the battery? Or do you mean run off the inverter at all times?

The power supply in my PC is good. Here in the Philippines the electricity can go out 3 times a day or be on for weeks at a time.
lemonie WWC5 years ago
Yes, have the inverter running all the time - the power will be from either the the battery or the mains-charger. The "un-interruptable" bit is largely achieved by not physically switching supplies.