Formula for calculating run time of apc ?

Simple except for one missing piece of info. How efficent is the system ?

The Ah (amps the battery can put out for one hour). As Amps and voltage equals watts, your battery is rated for 12 times 18 or 216 watts for one hour. So you get 216 devided by 120 or 1.8 hours. Then multiply by the efficency (loss of the system) that is unknown, but 50 to 80 percent would be inthe ball park. So at 50 % you get half of the 1.8 hours or .9 hour.

All that is provided the battery can put out enough current to last that long. Often the more current the battery is required to put out, the less time it will last.

Thanks.

It ran for an hour just on the battery backup.

It said I had around 15 mins left when I went back to A.C. power.

Andy

UPS batteries have to provide the magnetizing current for the big iron transformer, so battery life is disappointing at light loads. Nowhere near as good as a DC-DC converter.

Cheers

Phil Hobbs