I Love Electricity

Power Conditioning for Computers

This was my UPS stack up until yesterday. There are 7500va of Liebert Dual Conversion True Sine units there. I certainly don’t have that much stuff plugged in, but I needed the runtime. The combined total of 26 12v 7ah batteries in them gave me plenty of time to get the generator started when the power fails. I had my loads evenly distributed amongst them (Server, NAS, workstation and gaming rig, plus the entire A/V theater system w/projector.

I wired in a dedicated circuit for them. A 12awg/20a/120v circuit was enough because I only have 1300w-1500w of load.

I re-built my own battery packs as well. Much less expensive by some order of magnitude to buy boxes of batteries in bulk rather than the “official” ones.

Then I scored this beast. It’s only 3000va BUT it has 16 12v 7ah batteries in it. That’s a nice run-time…and I only have it about 30% loaded at the most. I have my newest Liebert with expansion chassis (12 batteries) for the Server and NAS (seen on top), and this huge one for the rest of the office and theater equipment. This replaced the 3 older Liebert units shown earlier.

I wired in a dedicated circuit for this 240v one as well (I wired in 120v receptacles in the UPS for the equipment)

Switched 240v receptacle so I can isolate from the generator when necessary but remain grounded (whereas unplugging cuts the ground)

The new UPS is special because it’s also fully isolated with this giant transformer. So I have a dual conversion, true sine and fully isolated power source for my rigs 😀

Nice power condition capacitors in there too!

As a side note….UPS batteries last about 5 years, provided they aren’t discharged too often. This is why I tell people not to do “diehard tests” on their UPS units to see how long they’ll last. When the batteries finally go, they may leak acid like this one did, or even bulge and puff up. I’ve seen UPS units physically distorted and destroyed due to battery bulging. This usually happens with the cheaper ones you’d buy at a big box store, since most don’t implement circuitry to stop charging dead batteries…

A couple random UPS pointers:

-Avoid “modified sine” models as the output is super nasty and stresses electronics.
-Online or “dual conversion” units are better than “line interactive”, as there is no switchover time. Online models also condition the power the best, as they’re always going from AC to DC and inverting back to AC. The downside is they’re less efficient because there are more conversions.
-Isolated units use a transformer to keep your equipment physically separated from the grid, but are expensive.
-[URL=]VoltAmps are not equal to Watts[/URL] in the UPS world, due to power factor.
-Buying used units with dead batteries and re-building the battery packs yourself can save a ton of money…but can be dangerous if you aren’t familiar with electrical safety and working with batteries (you can’t turn batteries off so wiring is always ‘hot’).

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