general knowledge of types of UPS

[Anonymous user]

it is still true that the UPS provides backup power untill local power is restored
units were considered a backup source for power for short periods

are the units today running off the batteries all the time or does it switch to the batteries when the local power fails?

are they a "standby" or "backup" source?

[voidstar_apc]

It depends on the UPS.

Some, such as low-end SmartUPS and BackUPS are line-interactive and will generate AC only when the line goes away.

Others, such as Symmetra, are double conversion and are always on battery. The benefit of this is electrical disturbances on the AC line has no effect on the UPS output, but the downside is it's less efficient.

Lately, we're starting to see manufacturers with double conversion UPSes that "go green" by turning off the inverter while the AC line is good.

[Cap1_apc · Accepted solution]

Hello,

There is a very informative white paper discussing the types of UPS systems:
http://www.apcmedia.com/salestools/SADE-5TNM3Y_R5_EN.pdf

APC SmartUPS RT and Symmetra lines are indeed double conversion online. To make a minor correction to what Voidstar said: they technically aren't "on battery" 100% of the time. Double conversion online systems have a rectifier and inverter that are always in operation re-creating the AC power. The battery string is inline being charged (if necessary) but the UPS only uses the battery DC voltage if it needs to (in the case of a power outage where the DC coming from the rectifier is lost). The switch to battery DC is seemless and there is 0 transfer time. Take a look at figure 4 in the PDF for a clearer picture.

[Anonymous user]

thanks for the link to the APC White paper #1

figure 1 - for desktop / workstation PCs - suggest this is the most prevalent type as an (inexpensive) source for backup power. This paper was written 4 years ago, is it still current in today's real world? (something I'd see from the Walmart shelf)

Message was edited by: noJustice

[Anonymous user]

Anything you find at consumer retail outlets are most likely the standby type. Most of the improvement in UPSs since the 90s is the addition of USB interface and amount of information about UPS status available to the computer.

The actual guts, the batteries and inverter are on the cost reduction schedule, so UPSs you see today for the same VA size have smaller batteries and often time, the limited run-time of batteries limited the component heating to within limits.