Custom UPS Lashup


Custom UPS Lashup
Content © 2004-2017 ALH unless otherwise stated.


Custom UPS Lashup

So I decided my APC UPS was way too unreliable and decided to make my own, which is what people used to do before it came in a package. However, mine will not stay in phase with the grid frequency, (as if I cared), but it works great! Nothing but a float power supply, 12v SLA battery, high surge inverter, and a homemade switch box to switch to the inverter.

This is the proof of concept shot. At your interest, from this point, I will describe this lash-up from left to right if you continue reading. First, there's a regular car battery charger, a 12V 7AH SLA battery, and the high surge AC inverter (red) with the multimeter (yellow) below it. The charger, battery, and inverter input are of course connected in parallel. The 120VAC output of the inverter is connected to the wires on the socket (small upper white thing) with the hot connected to the NC pin on the relay (small lower white thing with all the alligator clips on it). The socket has a laptop with no battery plugged into it (not shown). The NO pin is connected to the 120VAC hot of the house/grid socket. [Both neutrals on the grid socket and the inverter socket are tied together, but the ground isn't connected on the inverter. This is because I didn't have an available double pole, double throw relay, just a single pole, otherwise the ground would have been shared, and both neutral and hot would have been connected to the relay.] The coil of the relay is powered by 24VDC coming form the silver bridge rectifier, which is powered by the transformer to the right of it, which is powered by the grid. ... And that's it! Turn off the AC grid power and the relay switches to the inverter. It won't be in phase with the grid, but who cares when computers have a switching power supply anyway? [I actually did try powering everything that has a switching power supply with 160VDC or so. Everything worked but my computer, which would start, but wouldn't boot. I didn't bother to mess around with it's power supply though.]