UPS backup time

HEllo everybody,

I am new here.

I have a question regarding my ups battery backup time. i have:

1 LOcal made ups of 1200watts

1 Ags 200ah 12v battery (3-4 months old)

my load is 400Watts (constant load)

Now my question is how much hours of backup I can get from my setup. Is there any formula. plz explain theoretically and practically.

Your reply will be highly appreciated.

Thanks

Nawaz

UPS backup time=battery AH * Volts/Load * 1/ Powerfactor

AGS 200 is approx 185AH battery

= 185 * 12/400 * 0.6 = 3.33 HRS Keeping in View of the inefficiency of the UPS 3.33*0.7= 2.5 HRS BACKup time will be around 2.5 HRS on This battery. Keep your charging Amp @ 18 A for optimal performance of the battery.