The UPS from Hell!!!!
DISCLAIMER: Kids don't try this at home. Lead-acid batteries produce a flamable gas when charged. Confining
this gas in a closed area with electronic circuits could cause ignition and explosion. You have been warned.
The UPS consists of three large lead-acid batteries and three APC 300 watt UPS circuit boards.
The lead-acid batteries are riding lawn mower type. A normal car battery would
have also worked. I picked the riding lawn mower type because they were the perfect
physical size for my case, and they have their posts on the side of the battery instead
of the top. The top of my case is aluminum and I was worried that posts on the top
might be shorted together by the top of the case (yeah, that would be a Bad Thing).
The plywood divider inside keeps the battery posts from touching each other. Since
the batteries on each side face each other, their positive and negative posts are adjacent to each other.
Should these get together and form a circuit this would also be a Bad Thing. (can you say "battery
meltdown or explosion"?)
The computers are plugged into the back of the UPS with normal household AC sockets.
The connector and circuit breaker on the right side of the case are holdovers from the case's previous life.
The APC circuit boards have their own breaker on the AC, and a fuse on the DC.
I have yet to find out how long this UPS will run my equipment on battery. I have run a 300 watt inverter and
a machine without monitor (about 60 watts DC into the inverter) on one deep cycle battery for about 20 hours.
This UPS is more heavily loaded, but has more battery capacity. I expect it will provide usable power for 8 to 10 hours.