[borner791]

It's more complicated than that. There are Smart-UPS online. Thats double conversion also 0ms transfer

Some of the "newer" online models will have a green mode, which although double conversion green mode introduces a transfer time (~2ms, basically relay lift time).

Backups are also square wave, or stepped sine Smart are Sinewave output.

This is specifically APC.

Also remember there are tare losses (copper / magnetizing and conversions), so a UPS just sitting there can use up to 30W.

[quesera]

Corroborated!

Back-UPS stepped sine wave has about 3 square steps above or below zero, so it's a very rough approximation of a sine wave. Adequate for many kinds of equipment, but ugly on a scope.

There is, or used to be, a pin on the Smart-UPS line that you could tie high (or low?), to tell the device to operate in "Online" mode (inverter always active, line power continuously tending the battery). APC also sold it preconfigured that way as a separate, more expensive, product. :)

There's also a trick to jump-starting an unplugged-but-charged Smart-UPS. I've used this for several hours of remote power in inconvenient locations.

Quality devices, but test them regularly. The switch from idle to high-draw can be violent, and it takes out weak components. Similar to tungsten lightbulb filaments.

[yardie]

Oh, I know very well it's complicated. But that is the 500ft explanation I give to the beancounters, "why are we using these expensive UPSes when we can get them for $100 from Office Depot."

I'm most familiar with the APC line because that is what I use.