how will calculate ups backup?

Answer 1

If you go to the APC website, they have a "help me choose" feature that calculates what kind of battery backup you need.

Here's the link.

http://www.apc.com/tools/ups_selector/

Answer 2

I assume that you are asking how to calculate how long a Universal Power Supply will last.

1. Assumptions: you are in the US (power factor of .8 lagging) and use 120VAC for your equipment.

2. My RS-1500 UPS, from APC, has a max rating of 1200 watts (1500 VA*.8 pf) for 4 min (ratings vary by manufacturer). My computer consumes 3.5 amps or 434 watts (3.5 amps*120 VAC * .8 pf).

3. 1200 watts * 4 min / 336watts = ~14.28 mins which coincides with my manufacturers specs.

4. Rule of thumb is that if you half the loading, run time on the UPS goes up by a factor of 3.
(Note US Manufacturer give a watt rating that is only ~60% of the VA rating as a deterrent against overloading. My figures are based on full load capabilities.)

Hope this helps!

V
US Navy Power Plant Operator/Supervisor 12years and running.

Answer 3

Typically you need to size a UPS about 125% larger than the nominal load. Example: You want to back up a 300VA load (typical PC), you would want a 375VA UPS.
Does this help?